EPA-670/2-74-002
February 1974
Environmental Protection Technology Series
Feasibility Study of a
New Surface Mining Method
"Longwall Stripping"
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
H. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
EPA REVIEW NOTICE
This report has been reviewed by the Office of Research and
Development, EPA, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policies of the Environmental Protection Agency, nor
does mention of trade names or commercial products constitute
endorsement or recommendation for use.
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EPA-670/2-7^-002
February 1974
FEASIBILITY STUDY OF A MEW SURFACE MINING METHOD
"LONGWALL STRIPPING"
By
Henry F. Moomau
Frank R. Zachar
and
Joseph W. Leonard
Contract No. 68-01-0763
Program Element No. IBBQij-O
Project Officer
John J. Mulhern
Mining and Land Modification Branch
Office of Research and Development
Washington, D.C. 2C460
Prepared For
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
For sale by the Superintendent at Documents, U.S. Government Printing Office, Washington, D.C. 20402 • Price $1.15
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ABSTRACT
"Longwall stripping" is a new surface mining concept developed
by the Environmental Protection Agency. Longwall stripping adapts
existing underground longwall mining technology for use in recovering
shallow cover coal without the total environmental disturbance often
associated with surface mining. This study investigated the environ-
mental, mining and economic feasibility of longwall stripping.
Longwall stripping was determined to be a feasible method for
mining coal under shallow cover. A discussion of the criteria that
is necessary to consider in selecting a site and developing the mining
plan is included. Additionally, alternate methods of the longwall
stripping concept are discussed.
This report was submitted in fulfillment of Contract 68-01-0763
under the sponsorship of the Office of Research and Development,
Environmental Protection Agency.
ii
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CONTENTS
Section Page
1 Conclusions 7
2 Recommendations 2
3 Introduction 4
4 State of the Art 5
Literature Survey 5
Strata Considerations 5
Equipment Survey 8
Current Practice g
5 Site Considerations ]]
Site Selection Guidelines 11
6 The Mining System 13
Health and Safety 13
Self Advancing Hydraulic Roof Support 13
Cutting 19
Conveyors 20
7 . Economic Evaluation 21
8 Alternatives to the System 24
9 Research Needs 25
10 Acknowledgements 27
11 References 28
12 Appendices 30
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FIGURES
Page
1. Plan View of Longwall Stripping System 14
2. Typical Cross-Section View of Longwall Stripping 15
System
3. Cross Section View of Longwall Stripping System 16
Along Highwall
4. Various Types of Terrain Applicable to Longwall 17
Stripping System
iv
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SECTION 1
CONCLUSIONS
1. Longwall stripping 1s a technically feasible method for extracting
coal at shallow depths utilizing present technology for some known coal
seams.
2. Longwall stripping utilizing present technology 1s feasible for
either area or contour surface mining.
3. Longwall stripping for shallow cover coal will produce significantly
less environmental disturbance than other known mining methods.
4. The economics of longwall stripping will be dependent on the rate
at which coal can be produced. This rate will be Influenced by the
physical conditions of the site and the application of equipment and
systems. Economic feasibility will also require either ample contiguous
reserves or numerous, scattered reserves which will enable rapid place-
ment and removal of the longwall system. However, it 1s concluded that
where longwall stripping is applicable the cost per ton of coal at the
mine will be less than produced from large deep mines but more than
from most "conventional strip mines."
5. Longwall stripping and its variations, if developed, can be utilized
in many coal reserves that are presently surface mined. It can also be
used for recovering coal from many areas where either surface or under-
ground mining 1s not pernrlssable or practical.
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SECTION 2
RECOMMENDATIONS
1. In order to establish meaningful environmental and operational data
it is recommended that a demonstration mine be implemented.
2. The following mining conditions are recommended for the first'
demonstration of this method:
(a) The coal seam should be at least 48 inches thick with
economics improving with increased thicknesses.
(b) A strong eight to ten foot thick sandstone or consolidated
shale member immediately above the coal is preferred.
(c) The floor should be strong, preferrably shale, and
reasonably impervious to water.
(d) A flat or slightly upward pitching coal seam with surface
topography conducive to good drainage and drainage ditching
is preferred. This will reduce the tendency of slush or
mud to enter the mine through fissures caused by caving,
thus avoiding or minimizing the need to install pumps and
discharge lines.
(e) The coal seam should be of uniform thickness and be free of
serious undulations or heavy pyritic intrusions.
(f) A readily marketable coal.
3. The following are the recommended factors to be considered in
selecting equipment for the first demonstration mine:
(a) A drum shearer, mounted over and travelling on or along
the conveyor pan, should be used. Consideration should be
given to the use of a double drum ranging arm shearer because
of its higher production capacity over a single drum shearer.
However, the double drum shearer will require a thicker coal
seam.
(b) Chocks and conveyors should have ample cross-sectional area
between front and rear legs to permit installation of a 24
to 30 inch diameter ventilation tube between the hydraulic
legs in order to provide at least 3,000 cubic feet of air per
minute delivered to within 10 feet of the inby end of the face.
Additionally, there should be room for the movement of men
between the chocks and the conveyor.
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(c) Chocks should be selected to quickly move under the newly
exposed roof behind the advancing shearing machine in order
to provide immediate roof support.
(d) Chock movement in groups by bank control could be used.
(e) Chock movement by remote control should also be considered.
(f) Heavy duty chocks, capable of being regulated as to yield
pressures, with wide canopies to achieve maximum roof coverage
and minimum psi at yield loads are recommended. The base area
should be ample to minimize floor pressure at the yield rating
of the chocks.
(g) Because of the critical nature of the outby area (highwall)
it is recommended that buttress supports, packwalling, or
stowing, special shielding, resen bolting or other highwall
support methods be considered.
(h) A continuous and steady operation preferably three shifts
per day, five days per week is recommended to reduce the
possibility of stress build-up due to settling over long
idle periods.
4. It is recommended that after the site has been selected, and prior to
finalizing the mining plan consideration be given to the variations of
longwall stripping in particular "shortwal! stripping."
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SECTION 3
INTRODUCTION
The long-term and more recent dramatic increases in the production
of coal by surface mining methods has caused concern over environmental
degradation in many areas. The recent dramatic increases in surface
mine produced coal can easily be seen between the years 1969 and 1970
when production increased from 197,023,000 to 244,117,000 tons, a
one year record unprecedented in the history of the coal industry of
the United States." More current records show a continued increase
in strip mining activity to reach a new high of 259,000,000 tons for
1971, which accounted for 46.9 percent of the total U.S. coal production.
During 1971 an additional 316,200 acres or 4,650 acres per week were
disturbed by surface mining.2,3
The present alternative to surface mining for coal 1s underground
mining. While this method for mining coal could possibly supply
the coal requirements of the Nation, it to is beset with problems.
However, the scope of this study is not to focus on the possibility
of abolishing strip mining nor an investigation of one mining method
versus another, but to determine the feasibility of a new surface
mining method, often called "longwall stripping," that can substantially
reduce environmental disturbance. Mining in this manner is visualized
as allowing needed strippable reserves to be recovered with a minimum
of disturbance to land and water resources.
The new mining method, longwall stripping, was developed by EPA as a
possible answer to some of the problems caused by surface mining.
(Refer to Appendix A). If a conventional longwall mining system could
be advanced at right angles to a narrow trench or along a strip mine
highwall, a number of benefits important to the environmental and
energy crisis could be achieved. Strippable coal could be mined
without destroying all the overlying vegetation. Such a mining system
could also achieve complete coal extraction, total resource recovery.
This greatly reduces the chance of long-term environmental problems
such as uncontrolled subsidence and acid mine drainage. The resulting
caved area should be more completely sealed, reducing or eliminating
the channels which act as tributaries for the eventual release of
acid mine drainage.
This study discusses the economic and technical feasibility of longwall
stripping and presents the conditions that should be considered in
demonstrating this new mining method.
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SECTION 4
STATE OF THE ART
Literature Survey
Some information 1s available In the literature on the general subject
of strata control relating to the strati graphic action likely to develop
in longwall stripping. Part of this information relates directly to
shallow depth mining3*4'5*6 while the remaining information involves
situations such as extracting coal from destressed areas that have been
previously under mined.7»8,9 However, information on longwall mining
systems running under extremely shallow cover or "open end faces" is
minimal and no experiences of longwalling with "open-end faces" is
recorded. A study of many technical articles and commercial brochures
covering longwall roof control has been made, and a brief discussion
of strata control follows.
Strata Considerations9'10'11'12'13'14'15'16'17
In longwall stripping the theories of strata control are somewhat similar
to those employed in conventional longwall mining in underground mines; the
immediate roof strata above the coal must be supported and allowed to
cave in such a manner to allow controlled support and caving of the
upper strata. As the longwall face advances, a desired sequence of events
should take place generally as follows:
(a) The immediate roof sags away from the stronger higher
strata.
(b) The immediate roof is relieved of the load of the upper
overburden.
(c) As the chocks advance the roof span increases until caving of
the immediate roof occurs creating a cantilevered shelf which
extends out from and is maintained by the supports, and a breaker
line is formed at or behind the chocks to shear and cave the
overhanding immediate strata.
(d) The caved immediate roof material expands to fill the void in the
mined area and the upper roof forms a span between the gob material
and a line where the immediate roof has separated from the
upper roof over and near the advancing wall face, conditioning
the roof strata for caving and the coal for mining.
(e) Most of the roof pressure is distributed between the solid coal
ahead of the advancing face and the gob. The supports merely main-
tain the relatively light load of the immediate roof.
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However, longwall stripping, as opposed to conventional underground
longwall mining, can be expected to be carried out under extremely
shallow cover ranging from 30 or 40 feet to not more than 200 feet
from outby to inby end of the face, while conventional longwall mining
is generally done under 400 or more feet of overburden. A combination
of (a) massive or too competent roof strata that had not been subject
to the normal conditioning stresses imposed by heavier and deeper over-
burden, and (b) shallow cover, will generally require heavier duty chocks
than deeper coyer longwall mining conditions, and the need of heavy duty
roof supports in longwall stripping can be anticipated.
On the assumption that sites selected for longwall stripping will have
general roof, bottom, and gradient characteristics to warrent a demon-
stration application, we would expect fairly normal roof action along
the face except on the outby or open end.
When the chocks are in place in the initial development entry the exposed
roof will be supported on the solid coal to be mined, the chocks, and
the solid coal behind the chocks. As the longwall face advances, the
width of the strip of unsupported roof behind the chocks will increase
and remain up, but with some deflection, as a uniformly loaded beam
supported by the back canopy of the chocks and solid coal. Deflection
will vary according to strata acting as the beam, and when the width
of the opening is increased to the point that the strata will no longer
support the uniform overburden load, the strata beam will fail, usually
in shear, to form the shelfs at the back end of the chocks.
It is anticipated, with an open end face as in longwall stripping, that
the deflection of the roof strata at the outby or open end of the face
could cause horizontal movement of the unconfined strata resulting
in a fall of overburden out into the faced up area where the longwall
controls, pumps, and face conveyor discharge end are located. For this
reason, it is anticipated that special "buttress" chocks and possible
packwalling will be necessary at the outby end of the face.
Prior to the failure of the roof strata behind the chocks and when the
unsupported width of the open area is at its maximum, a maximum load
will be imposed on the back legs of the chocks. The ability of the
roof strata to remain unsupported will vary from strata to strata
and chock yield loads and structure strength should be sufficiently
high to withstand what is commonly known as the "pressure wave."
After the initial failure of roof strata in shear behind the chocks,
the roof will then be supported by the unmined coal face and the chocks.
As the face advances and chocks are moved ahead, the strata left unsup-
ported will hang back and act as a cantilevered beam supported on the
chocks with the unsupported end extending back into the mined area or
"gob." If the immediate roof strata is sufficiently strong so as to
resist failure in shear and hangs back a long distance into the gob,
the resultant total overburden load on the back of the chock could
become very high until actual failure in shear behind the chocks occurs.
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Sufficiently heavy duty chocks can overcome this load along the interior
of the face, but again, special "buttress" chocks and a packwall at the
open end of the face are anticipated as necessary to eliminate this
high cantilever loading at the outby end of the face, with resultant
horizontal movement and collapsing of the overburden along the highwall.
In planning longwall stripping along the outcrop of a coal seam it is important
to recognize that weathering and surface seepage may have made the immediate
roof strata and bottom strata less firm and solid than those same strata
would normally be at greater depths. This, of course, will vary from
seam to seam, but in general, must be taken into account when chock
bearing areas, top and bottom, are selected so that proper variability
of yield loads is provided. The chocks roust support the roof, but
must not allow the roof to be crushed or the bottom penetrated when
the chocks are set or when loads approaching yield load are imposed
on the chocks during the so called "pressure waves."
Since the possible necessity of packwalling the outby end of the
longwall stripping face behind the chocks to prevent excess stresses
that could cause horizontal movement of roof strata and consequent
highwall collapse is recognized, a system, method, and means of doing
this must be provided. There appears to be several options such as
(a) building packs manually with timber, concrete blocks, rock, etc.,
(b) pushing dirt and rock into the mined area mechanically, (c) crushing
and blowing mine waste material using pneumatic stowing systems currently
in use in Europe, and (d) using a precrushed material such as power fly
ash and pneumatic stowing equipment.
Considering all the apparently desired factors for the first demonstration
mine it is suggested, due to the low cover, the open end face and mining
an outcrop area, that successful longwall stripping could most likely be
carried out in areas having the following general physical characteristics:
(a) A firm coal seam of fairly uniform thickness between 48 and
72 inches, relatively free from pyritic intrusions, and
fairly level or slightly rising from the outcrop in the
proposed mining direction.
(b) An immediate roof strata of a fair to medium sandstone
or firm shale between 5 and 10 feet in total thickness.
(c) A firm strata of laminated shale, 8 to 10 feet thick
above the immediate roof. This strata, along with
the immediate roof in (b) should be firm enough to allow
almost vertical walls when the outby bench is formed.
(d) A firm, fairly hard bottom, somewhat impervious to water,
which parts freely from the coal.
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While the above characteristics are desirable and are recommended as
necessary for any demonstration site, it is quite likely that, as more
experience is gained in the art of longwall stripping, methods and
equipment revisions and innovations can be made to overcome most physical
shortcomings of the seam and strata.
Equipment Survey
Longwall systems have advanced from the old heavily timbered longwall
employing center packs to the manually placed mechanical jack and,
most recently, to the modern self-advancing hydraulic roof support
system.17,18,19,20,21 Modern longwall offers many options and, when properly
applied, is known to be capable of achieving outstanding production
performance. This outstanding record is frequently achieved because
companies tend to place longwall systems in reserves of the highest
physical quality. This choice is especially timely when the instal-
lation represents a companys first application of a longwall system.
Builders of modern longwall systems offer many options to increase
potential for successful application. (Refer to Appendix B). The
optimal mating of these options to stratigraphic conditions is the
key to a successful installation. Some currently available options
and conditions that commonly lead to their selection follow:
Coal Getting Machines
Cutters and Plows - Where applicable, plows are the preferred
method for cutting coal. Conventional plows find application
with friable coal and/or with coal under deep cover, where
advantage can be taken of the natural crushing action that takes
place as a result of the high arch pressure along and behind
the coal face. Plows are capable of operating in thin seams
under 48 inches and they do not require an attendant while in
progress at the face. Because plows generally merely shave or
plane a coal seam, the resulting narrower web exposes a minimum
of new roof with each pass. Hence, the self advancing hydraulic
roof support system does not need to extend as far back toward
the gob area and, therefore, requires less elaborate and robust
construction than an equivalent shearer equipped section.
Finally, plows do not tend to grind coal as do shearers and,
therefore, in some applications they produce less gas and dust.
However, plows need a tail entry or an offset opening, generally
called a "stable hole" on the inby end of the face to cut into
if unidirectional or to turn around if bi-directional, and this would
be a handicap to the initial demonstration of longwall stripping.
Several new type plows are in successful operation in the United
States and Europe in mining conditions that have been traditionally
considered unappropriate for plowing. This success could broaden
the use of plows and result in additional options to increase the
flexibility of longwall mining.
8
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Shearers - Shearers were developed to facilitate longwall mining
in the many physical conditions that could not be worked with
plows. The shearer is the most popular coal winning machine used
in longwall mining throughout the world. It can be used to mine
either narrow 12" webs or up to about 30 inches as determined by
conditions. Shearers are fairly compact machines, self-propelling,
and with ranging arms, capable of readily adapting to changes
in mining height or gradient. Recent experiences in this country
indicate that these units generally require less total horsepower
per ton/minute capacity than do our continuous miners, and shearer
maintenance costs have been proven satisfactory. Actual pro-
ductivity of the shearer is simply determined by the depth and
height of the cut and the cutting speed along the face. Generally,
it has been seen that transportation facilities outby the long-
wall faces are the limiting factors in achieving shearer productivity.
Self Advancing Hydraulic Roof Support Systems
Chocks and frame supports are currently used in America. Chocks are
almost entirely used with shearers while either chocks or frames are
used with plows. Frame supports are highly flexible but require
skillful operations to maintain alignment as the face advances. Chocks
are aligned with the conveyor and require less operational skills.
Self advancing hydraulic roof supports can be obtained with various
options including immediate roof support capability behind the advancing
cutter, walkway between the conveyor and props, bank control for semi-
automatic chock advancement, oversized bearing surfaces for the
roof or floor, heavy duty hydraulic legs, choice of prop and
bearing surface configurations, extendable front and rear supports,
slush guards, etc. Where very friable or fractured roof con-
ditions exist, roof strata breaking up and falling into the
chocks can be quite a problem. To counteract this, new designs
incorporating "flushing shields" have been marketed and used
successfully.
Conveyors
Conveyors account for only a very small percentage of the total
downtime in longwall installations. Longwall conveyors generally
consist of a heavy single or triple strand drag chain with center
mounted and evenly spaced flights positioned within a rectangular
trough extending the full length of the longwall face. One important
consideration is the "snaking" length of the conveyor. A short
snaking length has advantages in that, with some hydraulic support
systems, more rapid roof coverage can be achieved. This advantage,
however, may be offset by the tendency toward greater conveyor wear.
Current Practice
Longwall mining with self-advancing hydraulic chocks had its first
U.S. application in West Virginia in 1960. European miners had little
choice but to utilize longwall mining, but in this country longwall
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had to compete economically with high production room and pillar systems.
The productive potential of this mining method is now recognized through-
out the industry and a little over 4 percent of our total tonnage now
comes from longwall faces.
European mines generally have conditions which are extremely difficult
to hold pre-driven entries open and consequently employ advance long-
walling wherein travel and haul ways are created by supporting areas
in the gob behind the advancing face. However, in this country, with
better conditions and high production entry driving equipment, travel
and haulways are pre-driven and the longwall face "retreated" between
sets of entries.
The advent of more comprehensive regulations regarding personnel
protection from roof and dust along with more rigid required ventila-
tion practices have increased the interest and incentive for U.S.
mines to adopt longwall mining. Today there are over 50 longwall
faces in operation with shearer faces outnumbering plow faces, and
extreme interest indicates a rapid increase in the number of faces
in the near future.
All longwall faces are in underground operations with face lengths
varying from 300 to 600 feet in length and under cover of from 200 to
2500 feet or so in isolated cases. As stated previously, no experience
has been gained in operating an open end face as contemplated in long-
wall stripping.
In almost every instance, operating companies indicate that their
lowest cost underground production is from longwall faces. Additionally,
much higher coal recovery is possible from the longwall system of mining
than from conventional room and pillar methods.
10
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SECTION 5
SITE CONSIDERATIONS
Site Selection Guidelines
With the first attempt at longwall stripping, a site in a flat area
or in a mountainous area with long, straight valleys where the coal
is located close to the surface or valley floor should be considered.
A long and straight strip mine highwall also offers a potentially
attractive site for the first demonstration mine. While longwall
stripping could probably be used to run a contour where the face
would necessarily turn to follow the outcrop, it is suggested, that
because of the many mining and environmental problems that will
require sound engineering solutions, this first mine only consider
a straight run operation. This of course is not meant to imply that
production rates would not decrease when turning. However, since
ample evidence exists that longwall faces are being turned this problem
should not be one of the more critical. Longwall mining equipment
systems offer enough options that mining should be technically
feasible under most conditions. Additional considerations for this
first demonstration mine are as follows:
1. Reserves should be ample to insure that equipment can be profitably
depreciated.
2. The site should be accessible and means should be available
to transport the coal to previously established markets.
3. Physical features associated with the site that are considered
to be desirable are a coal seam between 48 inches and 72 inches thick.
A strong sandstone or shale member, perhaps 8 to 10 feet thick, should
be located over the coal. Additionally, a strong 15 foot thick shale
located above the sandstone, especially on the outby side, is desirable.
The floor should be strong. A flat or slightly upward pitched seam
can facilitate drainage and reduce or eliminate the need to install
face pumps. Surrounding surface topography should be conducive to
good water runoff to lessen the possibility of mud and slush from
entering the mine through fissures caused by the shallow caving action.
Also, the coal seam should be of uniform thickness and free of
undulations and intrusions.
Areas For Possible Application
It is not possible to produce authoritative estimates of areas of the
United States where a successful longwall stripping system could be
employed, since the full range of conditions under which this system
or variation can operate is not yet known. Methods used to report
strip and deep mineable reserves are based on certain present and
presumed mining equipment systems and economics. Strippable coal
11
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occurs in 28 of the 50 states. The state with the most strippable
reserves of coal, regardless of type, is Wyoming (13.971 billion
tons) followed by Montana (6.897 billion tons), Alaska (4.411 billion
tons), Illinois (3.247 billion tons), New Mexico (2.474 billion tons),
West Virginia (2.118 billion tons), North Dakota (2.075 billion tons),
Kentucky (1.758 billion tons), Texas (1.390 billion tons), Missouri
(1.160 billion tons), Indiana (1.096 billion tons) and Ohio (1.033
billion tons). Reserves of approximately 3.451 billion tons are
located in the remaining 16 states.zz
A most likely location for the application of a successful longwall
strip mining operation would be in a rural area containing the com-
bination of shallow, presently strippable coal reserves coupled with
rich agricultural or forested lands. Such an area should also be
located near population centers, rail heads, river or power plant,
where the coal would most likely be used. Coal in these locations
should be of suitable thickness (between 4 to 6 ft.), and a well
developed system for distribution of the coal to surrounding markets
should be in operation. Coal reserves that most appropriately fit
the preceding description occur in greatest abundance in Illinois,
West Virginia, Kentucky, Missouri, Indiana and Ohio.
12
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SECTION 6
THE MINING SYSTEM
The objective of this feasibility study was to determine how longwall
stripping could be utilized in recovering shallow cover coal with
minimal environmental damages. Several constraints were placed on
the study of which the most Important from the mining consideration
was the use of existing equipment. Additionally, if the concept was
determined feasible, a mining system was to be suggested that could
be utilized in a demonstration mine proving the concept. While the
suggested mining system may not demonstrate the answers to every
question, it is believed that a successful demonstration of this con-
cept will provide the answers to the major questions posed in a mining-
environment balance.
It is proposed to open a long, straight and narrow trench into a coal
seam In a flat area or slightly above the floor of a valley, and long-
wall strip at a right angle to the side of the trench. This should
allow extraction of coal with minimal disturbance to the environment
and be economically feasible. Figures 1 through 4 are included to
illustrate arrangements that might be used in a demonstration of longwall
stripping. Because this concept involves a number of mining considera-
tions, each consideration is discussed separately in the following
sections.
Health and Safety
Whether the seam is opened and the longwall equipment set up in an
open trench or in an entry driven in from the highwall, the ventilation
of the longwall face seems quite simple. The installation of a suit-
able portable exhaust fan outby the entrance to the face with suitable
tubing extending through the chock line to the tail end of the face
should assure a minimum of 3000 cfm of fresh air continually flowing
inby along the face and into the tube at the tail end.
Since all personnel would normally be outby the shearing machine during
mining, any dust produced should be carried toward the tail with the
fine dust being picked up by the ventilation tubing and discharged into a
dust collector located outside. The fan location would be such as to avoid
the possibility of recirculation.
All personnel required to be underground during mining or for any
reason would be continually under the steel chock canopies and not
exposed to unsupported roof.
Suitable emergency controls, lights, paging or communication systems
etc. would be installed even though the end of the face would be only
about 250 feet from the surface opening.
Suitable personnel protection from any highwall material would be
furnished by self advancing steel canopies of proper area and design.
13
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BUTTRESS
CHOCKS
- -TOP OF SANDSTONE
- ^ (EXPOSED} .' -
^ FOR ,,-
^CjCONTROLS, V,
PUMPS, ETC.
BACKFILLED TO
ORIGINAL CONTOUR
iooou-—
Figure I - PLAN VIEW OF LONGWALL STRIPPING SYSTEM
14
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SURFACE
\\\
\v\vv
SOIL
SECTION A-A
Figure 2- TYPICAL CROSS-SECTION VIEW OF
LONGWALL STRIPPING SYSTEM
15
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SURFACE
uv
SOIL
SECTION B-B
Figure 3- CROSS-SECTION VIEW OF LON6WALL STRIPPING
SYSTEM ALONG HIGHWALL.
16
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HILL AND VALLEY
BENCH
/
BENCH
LEVEL
BENCH
ISOLATED ELEVATION
BENCH^-rf'.....:r... ,_---.-vV -t v-W x- , ";'•-. v.V/^-v
Figure 4- VARIOUS TYPES OF TERRAIN APPLICABLE TO
LONGWALL STRIPPING SYSTEM
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Self Advancing Hydraulic Roof Support
Since production from longwall faces depends on the successful
operation of three interlocked systems involving hydraulic roof
support, cutters and conveyors, the failure of any one system will
cause production stoppages. Of the three systems, the hydraulic
roof support is undoubtedly the most critical. Chocks or frames
are used for hydraulic roof support. Chocks, which are most
applicable to this project, should have sufficient area between
the front and back legs to permit extending a 30 inch diameter
ventilation tube to within 10 feet of the inby or solid end of the
longwall. The size and bearing capacity of supports used in shallow
mines are always constructed for the heaviest duty, and similar
applications in longwall stripping would be no exception. It is very
important that when a chock is lowered, the roof remains in place
long enough to permit the chock to be placed back to its original
elevation. If the roof is punctured and settles around the chock
or if the roof converges, the chock will be repositioned at lower
and lower elevations and eventually be unable to advance. Therefore,
large roof and floor bearing surfaces should be used. Additionally,
to minimize the load on the chocks, the chocks should be selected to
minimize the length to which they extend back away from the face and
into the gob. However, this extended length should not be restricted
so as to interfere with the movement of men or with the placement of
the ventilation tubing.
Since the most critical area for the mine is at the outby end, or
entrance, three or four chocks should be equipped with cantilevered,
buttress supports extending back into the gob to help control roof
breakage and facilitate orderly roof failure along this critical highwall
area. Frame type or self advancing canopies may be useful for pro-
tecting men from rock falls along the highwall adjacent to the entrance
to the longwall. Additionally, consideration should be given to a
combination chock "highwall canopy" for additional safety.
In order to maximize the roof control, a system that will permit
the advance of chocks immediately behind the shearer as it passes
should be considered. This feature is particularly desirable where
bad or friable roof is involved. Some designers believe that the
potential answer to close in roof support should be sought through
the use of a shorter snaking conveyor.
Although complete automation of the operation of the chocks from the
trench is possible, such a feature may not, at this time, be needed.
Instead a bank controlled method of automation for moving the chocks
should be considered. With this method only one man is used to advance
six to ten chocks from a single position. With bank control, all
of the chocks along the longwall face could be moved by a single
miner from different positions resulting in a less expensive, auto-
mated chock system. Another factor in the decision to automate the
18
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chocks, is that underground visibility is considered to be limited
to 10 meters, about 30 feet, and this distance is equivalent to the
length of 6 to 10 chocks. Hence, the bank control of 6 to 10 chocks
would result in a form of "on-sight" automation.
Shielded chocks, although more costly, may find application when
longwall stripping in areas containing unconsolidated strata above
the coal seam. Roof strata of this type would be ideal from the
standpoint of ease and economy in uncovering the trench, however,
problems are envisioned if an entry is driven for the initial set
up of the longwall. It is entirely possible that future developments
could favor longwall stripping of shallow seams with extremely loose
overburden using shielded chocks.
Although hydraulic roof supports seldom fail, when they do fail it
is usually due to one of two causes:
(a) They become "solid" where the hydraulic prop is either gradually or
suddenly compressed to its lower limit and is therefore incapable of being
moved. This condition requires that the roof above the prop be shot-out
to permit removal, a very time consuming procedure.
(b) Hoses and fittings may rupture if excessive pressure is sudden
and/or if hydraulic releasing mechanisms are not fast acting.
Cutting
Unless both ends of a longwafl stripping mine are open to the fresh
air the use of a plow for longwall stripping should not be considered.
Moreover, plows work best with friable coal under deep cover where
the weight of the strata above tends to crush the coal making the
face more amendable to plowing. Therefore, shearers are considered
as the best choice-for cutting coal in the first demonstration mine.
The use of a double drum shearer which would cut coal in one direction
and flit back to repeat the cycle should yield the highest rate of
production. However, a single drum ranging arm shearer with the
drum on the inby end should be given serious consideration. Sumping
features for the double drum were not considered desirable, since
it can take as long to sump the double drum into the solid coal
at the back end of the wall as it would to flit the double drum
back. The use of a single drum shearer cutting the top of the seam
and then brought back along the bottom may not have the production
potential attainable with a unidirectionally operated double drum.
The automation of shearers has long been handicapped because of
consistent failure to develop a probe capable of sensing where the
coal ends and where the roof or floor begins. In the absence of
such a proven sensing device, it appears that existing technology
and economic constraints will require the shearer to pass three manned
chock stations. If these men are removed, then an additional research
effort will be needed to find methods to automate coal cutting with
shearers. While there is not presently a proven probe, current work in
this area may have advanced to a level for consideration during the
demonstration mining operation.
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Conveyors
Since the longwall stripping concept calls for a face conveyor 300
feet or less in length with the discharge end outside, It is likely
that a single strand conveyor, running at the proper speed, and
with one or two motors at the discharge end would be advisable for
the demonstration project.
20
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SECTION 7
ECONOMIC EVALUATION
A 250 foot longwall strip mine located in a 48 inch thick coal seam
should be capable of producing about 100 tons of coal per pass of the
shearing machine, assuming a 30 inch web cut. It should be possible
to make 4 to 5 passes to produce from 400 to 500 tons per shift for
an average shift production of 450 tons.
Although it is believed that as few as two men underground per shift
could operate the mine with automated chocks, under favorable con-
ditions, it is also possible that as many as six men might be needed,
under less favorable circumstances. If only two men were needed under-
ground, one man would be used to operate the shearing machine while
the other man would operate the automated chocks. If six men were
needed underground, two men would operate the chocks, one man would
operate the shearer, one man would assist with shearer operation as
a mechanic, one man would be stationed near the tail end and one man
would be stationed in or around the outside entry.
In addition to the underground employees, an outside force is envisioned
which could range from as few as two to as many as six men. If
only two men were needed outside, as a result of an existing exposed
highwall, one man could be a general mechanic while the other man could
be stationed at the outside end of the longwall. If as many as six
men were needed outside, to excavate a trench or highwall, one man
would be a dozer operator, one man a small shovel operator, one man
a grader operator, one man a rubber-tired loader operator, and two
men would be needed for stabilization of the highwall and for
operation and maintenance of outside coal conveyence and removal equip-
ment. Other combinations of manpower are possible, depending upon
conditions, but the range of manpower needs is believed to include
most foreseeable situations. The role of foreman could be combined
with one of the previously mentioned jobs.
In addition to the preceding manpower needs, most of all of the
following equipment would be required. Equipment is listed together
with approximate cost.
Underground Equipment
A. Chocks
56 - 4 leg 500 ton units 9 $ 9,000 each
4 - 4 leg 500 ton pack chocks 9 $ 12,000 each
4 - 4 leg buttress chocks e $ 12,000 each
1 - Power pack, pumps, tanks, etc. $ 18,500 each
1 - Set of line hoses and fittings $ 7,000
Remote control system $155,000
Stowing machine and compressor $ 50,000
Canopy at highwall $ 10,000
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B. Shearers
Single drum unit
Double drum unit
C. Face Conveyor
Basic price (250 foot long)
Accessories including ramp
plates, tube guides, spill
plates, etc.
D. Power Center and Controls
Surface Equipment
Shovel (2 1/2-4 yd)
Dozer with ripping attachment
High!ift
Grader
Drill
$160,000
$190,000
$ 40,000
$ 40,000
$ 50,000
$120,000
$143,000
$160,000
$ 80,000
$120,000
In consideration of two separate mining operations one being the
underground longwall face, and the second being the construction
of the .trench, an effort was made to arrive at an average cost for
the combination of production from both operations.
It is projected that the longwall face will progress approximately
33 feet per day. To accommodate this advance rate the construction
of the trench will also advance at approximately the same rate. The
trench width would be approximately 30 feet wide, progressing 33 feet
per day in a coal seam of at least 4 feet in thickness would produce
about 150 tons per day or approximately 36,000 tons per year. The
tonnage of the trenching operation, being at the outcrop, would be
blended with longwall mined coal or maintained separately depending
on available markets. In the following table of costs we have
inserted a cost of $10.00 per ton or $360,000 per year for all
outside construction which includes site maintenance and final
restoration.
Tons/shift
Tons/day
Tons/year
Tons/day
Tons/year
450
3x450 = 1350
200x1350 - 270,000
150
240x150 = 36,000
Total tons/year produced 306,000
Longwall labor
Longwall supplies
Longwall power
Longwall labor, supplies, power
longwall face
longwall face
longwall face
trench excavation
trench excavation
$0.875/ton
0.400/ton
0.200/ton
$1.475/ton
22
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Depreciation
Royalty (UMWA)
Taxes, Ins., etc.
Royalty (coal)
$0.750
0.800
0.400
0.500
Longwall royalties, depreciation, taxes, ins.,
etc.
Total Longwall cost
Total Outside cost
$2.450/ton
$l,059,750/yr $3.925/ton
$ 360,000/yr
Total production cost at site $l,419,750/yr
Trucking ($.80/ton)
Tippling or processing ($.25/ton) ._,—,,,.
Highwall stabilization (if necessary) 153,000/yr
$ 244,800/yr
76,500/yr
Administrative & engineering
Total cost of 306,000 tons
92.000/yr
$1,986,050 or $6.49/ton
NOTE: Estimates are based on 7-year equipment write-off
period using straight line depreciation. Labor is
estimated at $55 per man per shift. Costs are for
coal delivered to the mine loading bin and prepared
for delivery.
Costs might range substantially depending upon the mining conditions
encountered. These costs are comparable to some strip mining costs
and fall below most deep mining costs. If poor mining conditions are
encountered, even with well proven and long established mining systems,
mining ventures can be unenconomical. Hence, the success of a longwall
strip mine installation will depend as much or more on site selection
as with any other, less experimental, mining venture.
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SECTION 8
ALTERNATIVES TO THE SYSTEM
In the study of the concept of mining coal under shallow cover utilizing
underground longwall mining technology, several alternates or modifi-''
cations become readily apparent. The most significant development for
making this new mining method feasible was the recent advances in self-
advancing remote control roof support systems. With the ability to
control the strata above the coal now technically possible, several
alternatives to the original concept of longwall stripping appear viable
and possibly more attractive. These are:
1. A shortwall mining system which is a continuous mining machine and
a continuous haulage conveyor used to cut inward along the face and at
right angles to the highwall. The roof support system would be similar
to those previously discussed and are similar to those specially built
chocks that are presently being used with underground shortwall installa-
tions. The shortwall has all of the advantages of the longwall except
that supporting the ends would need further consideration.
2. By driving two shallow and parallel slopes, spaced 300 to 600
feet apart, into a surface mineable coal seam the longwall mining
between and behind the advancing slopes, would also appear to be
advantageous. The advantages are that it would not differ too greatly
from conventional longwall underground mining and, except for the shallow
location of the strata control techniques that need proven, should be
deemed less experimental. Very little vegetation would be destroyed,
since an open cut trench would not be needed. Additionally, since ventila-
tion would follow routine procedures, the limitations to longwall
stripping that may be caused by some local mining laws would be
eliminated. The disadvantage is that additional men and one or two
continuous mining units would be needed underground.
3. The use of a continuous mining machine coupled with the longwall
roof support system would have certain advantages and disadvantages.
The advantages are that the continuous mining,units could be used to
develop a single line of support pillars along the highwall to eliminate
the need for stowing while the longwall could be used inby the support
pillars to mine the solid coal. With the exception of the extremely
shallow mining, this approach comes close to the type of mining which is
presently practiced in the deep mining industry and, therefore, is
of a less experimental nature. The disadvantages would be that more
men would be required underground, and some acid mine drainage may
be released from the uncoilapsed, pillar supported, edge of the
highwall with possible long term environmental consequences.
4. The "stowing" of rock, fly ash, etc. behind the roof support system
instead of "caving." This would provide obvious environmental benefits
by replacing the void left by the mining operation with waste material
and preventing any subsidence of the surface.
24
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SECTION 9
RESEARCH NEEDS
1. The need for a demonstration mine to develop information which
could be useful for determining the optimal application of existing
equipment and to aid in the design of new equipment for longwall
stripping and its alternatives is obvious. Some of this needed infor-
mation is as follows:
(a) determine the overall environmental effects of this new
mining method
(b) the distribution of stress and ground movement both before
and after collapse of the main roof
(c) determine the effect of various rates of face advance
on strata behavior both with and without stowing
(d) determine the effect of periods of inactivity on strata
behavior
(e) determine the capability of sustaining high levels of
production
(f) analysis qf each job to determine optimal allocation
of work functions as a means to minimize underground
exposure
(g) analysis of the effects of caving on the surface vegetation
with and without stowing
(h) analysis of the quantity and quality of any water that
might be released from the caved areas with and without
stowing
(i) determine modifications and improve knowledge about the
selection of existing equipment
2. An important and seemingly attainable objective of longwall
stripping is to reduce or eliminate the exposure of men to underground
hazards. An examination of the potential of major design changes for
longwall systems in these applications should be considered. These
design changes should be directed at developing a less elaborate,
lower cost, highly productive system with the ultimate objective
of not requiring any full time employees underground with only
occasional entry to the mine for maintenance. To achieve this
objective more information is needed on:
(a) a compact and flexible roof support system which is
closely integrated with conveyor and cutter
(b) a system that can be inserted or removed from the highwall
and readily lengthened or shortened
25
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(c) a system more easily turned from a straight line of
advancement to maintain higher production.
(d) specialty equipment capable of preparing a trench while
minimizing surface degradation.
3. Longwall stripping of multiple coal seams.
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SECTION 10
ACKNOWLEDGEMENTS
Because of the novel nature of this research program and the absence
of information in the literature, most of the useful findings were
obtained from discussions with knowledgeable people in the mining
industry. Therefore, the following people who supplied valuable infor-
mation and assistance to this program are gratefully acknowledged:
M. Cariven, LaHouve Mine, Mellebach, France
A. M. Clark, National Coal Board, London, England
James Francis, Gullick Dobson Ltd., Wigans, England
James Gilly, U.S. Bureau of Mines, Washington, D.C.
M. Grison, Houilleres du Basin de Lorraine, Mellebach, France
Joseph Kuti, Mining Progress, Inc., Charleston, W. Va.
Walter Lubogatzky, Becorit Company, Germany
John Laabs, Westfaila Lunen Co., Germany
Berging H. Maucher, Rheinische Braunkohlenwerke, AG, Germany
Benno Niedzielski, Houilleres du Basin de Lorraine, Mellebach, France
Alan Purdy, Gullick Dobson Ltd., Wigans, England
Otto Renzing, Eckhoff Mfg. Co., Germany
Arno Schneider - Paas, Mining Progress, Inc., Charleston, W. Va.
Philip G. Weeks, National Coal Board, London, England
Ralph Cox, U.S. Bureau of Mines, Washington, D.C.
William Higgins, Gullick Dobson Ltd., Wigans, England
Cody Marsh, DEVCO, Nova Scotia, Canada
Jerry Hartly, DEVCO, Nova Scotia, Canada
Donald J. 0'Bryan, U.S. Environmental Protection Agency,
Washington, D.C.
William J. Lacy, U.S. Environmental Protection Agency,
Washington, D.C.
William Schimit, U.S. Bureau of Mines, Washington, D.C.
Paul Compenation, U.S. Bureau of Mines, Morgantown, W. Va.
27
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SECTION 11
REFERENCES
1. 1972 Keystone Coal Industry Manual. McGraw-Hill, Inc., New York,
New York.
2. Statement Before the House Interim and Insular Affairs Committee
by Louise Dunlap, Washington Representative, Environmental
Protection Policy Center, Washington, D.C., April 10, 1973.
3. Statement Before the House Interim and Insular Affairs Committee
by John L. McCormick, Washington Representative, Environmental
Policy Center, Washington, D.C., April 10, 1973.
4. Cothern, L. I., "Longwalling on Timber in Alabama Coal Mines,"
American Institute of Mining and Metallurgical Engineers, TP 1211,
New York, New York, June, 1940, p 200-210.
5. Aynsley, W. J., "Subsidience Observations Over Shallow Workings,
Including Pneumatic Stowing and Rapidly-Advancing Faces," The
Mining Engineer, April, 1961, p 522-564.
6. Evans, W. H. and Henshaw, H., "An Investigation of the Loads on
Packs at Shallow Depths," Transactions - The Institution of Mining
Engineers. Vol. XCVI. 1938-1939, pp 368-385.
7. Morton, J. W. and Watson, E. K., "Roof Control Under Advance
Conditions at Whitburn Colliery," Colliery Guardian, November 6,
1964, p 617-624.
8. Simes, D. J. and Jaggar, F. E., "Strata Control in Mining Operations
in a New Mine at South Bulli Colliery," Proceedings of the Fifth
International Strata Control Conference, 1972, p 1-9.
9. Deats, M. J., "A Follow-up Report on Longwall Coal Mining at
Durban Navigation Collieries (Pty) Limited," Journal of the South
African Institute of Mining and Metallurgy, April, 1971, p 179-189.
10. Adler, Lawrence and Sun, Meng-Chorng, "Ground Control in Bedded
Formations," Bulletin 28, Research Division* Virginia Polytechnic
Institute, Blacksburg, 24061, December, 1968.
11. Holland, C. T. and Cakir, Celaletten, "American Longwall Problems,"
Mining Congress Journal, November, 1968, p 30-6.
12. Adler, Lawrence, "Deflection of Mine Roof Supports," Mining
Engineering, October, 1959, p 1027-1029.
28
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13. Carman, C. 0., "Roof Action With Longwall," Coal Age, December,
1964, pp 80.
14. Carman, C. 0., "Understanding Roof Action is Imperative in
Longwall Mining," Coal Mining and Processing, March, 1965, p 38-42.
15. Singhal, R. K., "Longwall Strata Control," Colliery Engineering,
Juen, 1966, p 249-254.
16. Design of Mine Layouts - With Reference to Geological and
Geometrical Factors."Forking Party Report 1972, Mining Department
National Coal Board, Hobart House, London, England.
17. Subsidence Engineers Handbook. Production Department, National
Coal Board, Hobart House, London, England.
18. Kuti, Joseph, "Outlook for Longwall Mining Systems in the United
States," Coal Age, August, 1972, p 64-73.
19. Hess, Heinz, "Shield Supports as a Contribution to Continuing
Rationalization at the Face," Gluckauf, Vol. 108, No. 2, January
20, 1972, p 60-68.
20. Reid, William J., "Some Aspects of Practical Powered Support
Design and Use," The Mining Engineer, April, 1970, p 445-450.
21. Summary of Mechanization Trial With Drum Cutting Machine at
Shaft W2 of A. W. Wasson, Ltd., Rothwell, N. B., 1961-62.
Information obtained from the New Brunswick Department of Mines,
Fredericton, New Brunswick, Canada.
22. Bituminous Coal Facts 1972. National Coal Association, Coal
Building, Washington, D.C. 20036.
29
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Appendix A is a concept paper written by John J. Mulhern,
Mining Engineer, Environmental Protection Agency, Washirtgton,
D.C. This concept paper was the initial study of Tongwal.l strip-
ping and was part of the RFP bidders package dated March 23, 1972,
It is included by the authors as the initial reference and work
on longwall stripping.
30
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Longwall Stripping
Introduction
In the early 1800's miners on Mauch Chunk Mountain in eastern Pennsylvania
started a mining practice that has been used to extract millions of tons of
coal from the earth - surface mining. The practice of surface mining in
the United States goes back to this early beginning where miners with dynamite,
picks and shovels removed the covering earth to expose a seam of anthracite
coal. While the art of surface mining has been practiced for many years, it
is only (relatively) recently that technology has developed new hugh machines
that are capable of chewing deeply into the earth. These giant earth
movers can literally peel the earth to uncover coal as much as 150 feet
below the surface.
The extraction of coal by surface mining methods seems to be a simple
process. The overlying vegetation, dirt and rock are scraped, dug and
blasted to expose the coal seams. The coal seam is then brushed to remove
loose dirt and the coal broken or "ripped" for loading into trucks. When
the cover overlying the coal, called overburden, becomes too deep for the
earth moving equipment to economically move, giant augers are sometimes
used to mine further into the earth. These augers (large coal drills as
much as seven feet in diameter) penetrate many hundreds of feet into the
exposed edge of the coal seam. Hence, surface mining simply uncovers coal
seams for easy coal removal.
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Environmental Degradation
Sheer cliffs, barren land, overturned and fractured rocks, pooled water
that is blue-green with alage or brownish red with acid - iron, a few
deformed or mishappen trees, and patches of the more hardy weeds, are the
stark monuments of many surface mines. The monsters that chew rock and
earth to uncover the black mineral fuel, coal, have left their mark on
the countryside. Far reaching draglines, slicing bulldozers and giant
drills slowly chew their way into the earth. The earth that covered and
protected this coal now lies broken, heaped and scattered. The trees,
forests, farms and pastures have all yielded to the rape of the mechanical
monsters.
This devastation of land is not completely confined to that portion of
earth covering the coal but often extends past the coal to nearby areas.
The harmful effects on water spread downstream like tentacles carrying
the strip miners legacy, siltation and acid waters.
The vegetative cover, scraped off by the slicing bulldozers, once bound
the soils they grew upon, to the earth. With this protective cover removed,
even the gentlest rainfall may carry soil particles into the streams and
heavy rains or major storm events dramatically increase the amount of
sediment carried into the streams. The sediment load washed from strip
mined lands can be 20,000 to 40,000 times greater than from natural
forest lands.
The mechanisms through which sediment can impair the water quality and
reduce the quantity of available water supplies are well known. It is
enough here to remember that sediment reduces the food producing capa-
bility of a water body and its productivity, makes water less desirable
for water supplies, recreation and scenic values, and fills up impound-
ments and lakes^ destroying their usefullness to man and nature.
While "acid mine drainage" may also result from other mining activities,
it is readily apparent that surface mining contributes a substantial amount
of pollution to the Nation's waters. Acid water, and the associated metal
compounds, can kill the desirable aquatic life in streams and ponds. Most
aquatic life in placid lakes and running streams cannot survive in the
hostile environment of acid waters and these waters are often lost to other
uses such as boating and swimming. Additionally, as is so obvious, the
downstream municipalities and other water users must increase their water
treatment facilities (and costs) to make the water useable for their
residents.
Thus, the overturned earth and rock create problems to surrounding areas
many miles removed from the coal. As rains wash these stripped lands,
sediments and acid waters are carried into surrounding streams and rivers.
These water pollutants pass out of the immediate, coal lands to affect those
who are unfortuantely, "just downstream." It is estimated that 25% of the
mine drainage pollution in U.S. streams is caused by abandoned surface
mines. Additionally, 4800 miles of streams and 29,000 surface acres of
impoundments and reservoirs have been estimated to be seriously affected
by surface coal mine operations.
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Severe degradation of the environment is the heritage often left by miners
in many parts of Appalachia, and throughout the Nation. The barren de-
solation of unproductive land that was poorly reclaimed, if reclaimed at
all, stands as a monument to their efforts. It is said that in time nature
can heal all its wounds, but one must wonder, when looking at this utter
devastation that has been wrought, if/ man has that much time.
33
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Energy
Energy is the capacity to do work. It can be provided by man and animals
or fossil fuels, falling water or nuclear power. Man by himself can
provide the energy to do work but a ton of coal today, properly converted,
can produce more work in one hour than 1,000 men in the same time period.
The Nation's demand for energy in all forms is increasing at rates that
have exceeded most predictions. A three to four percent yearly increase
("historic rate of growth") has been erroneously used to predict energy
demands even in recently published "Energy Crisis" articles. Yet in the
past five years the annual growth rate in energy demand has been at least
5%, and since 1968, it has risen to 5.6%. This underestimating of the
Nation's energy growth rate is in large measure the real cause of the
energy crisis. The investment in new fuel and power production and dis-
tributuion facilities was geared to the historic rate of growth and,
consequently, the energy crisis is present.
Energy consumption can be divided into four major categories - industrial,
transportation, household and commerical and electric utility. Of these
categories, electric generation has been increasing the most rapidly. In
1955 electric generation was 547 million megawatt hours (1 megawatt hour
equals 1,000 kilowatt hours and is abbreviated kwh) and in 1970 it was
1,530 million mwh almost a threefold increase.
The Federal Power Commission (FPC) is the regulatory agency charged by
Congress to oversee the Nation's electrical energy needs. The FPC
projected an average annual growth rate of about 7% in the demand for
electricity in the 1960's. The FPC predicts that coal consumed by
electric utilities will increase about 4 to 5% per year reaching 472
million tons by 1980 and 615 million tons by 1990. If this projection
proves correct the utility industry alone will use more coal in 1990
than the entire coal industry produced in 1970.
As previously mentioned, an average annual growth rate of about 7% was
projected in the demand for electricity in the 1960's. Instead, since
1968, this growth has been around 9% per year. A 2% increase in demand
may not seem to amount to very much, but since it takes considerable time,
about 5 years, to build a power plant from conception to first generation
of electric,power, electric production is more than 10% behind demand.
The Office of Emergency Preparedness in mid-May 1971, released data
estimating net dependable generating capacity as of May 31, at 342,279 mw
with an estimated peak demand of 296,791 mr, and a reserve of 15.3% (this
reserve capacity compares with a 15.9% reserve capacity reported the pre-
vious year). However, these figures do not completely agree with those of
the FPC which reports the net dependable capacity as 326,677 mw with an
estimated peak demand of 257,419 mw. The reserve within the 15 to 20%
range that FPC generally considers normal to guard against unexpected
failures and higher peak loads than predicted.
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The FPC reported 43 power outages in official statisitics prior to June
1970, and only 15 in the last half of 1970. However, prior to June, all
power system failures over 25 mw (equivalent to the electric power used
by a community of about 40,000) were reported. However, on June 21, 1970,
FPC Order Number 331-1 became effective. This order redefines power
interruptions to be reported in order to increase the minimum report-
ing level to the lesser of (1) 100,000 kilowatts or (2) half of the
annual system peak load. With this revision to the reporting system,
official power outage statistics may not be easily correlated to past
performance or be readily related to the present "Energy Crisis".
The energy requirements Within the conterminous United States have been
estimated for 1990 by the FPC. The energy production requirements for
1990 are 5,828,000 mwh (5,828,000 mwh equals 5,828 gigawatt hours or
5,828 gwh) which is substantively higher than the 1,530,000 mwh produced
in 1970. While these figures show the demand for electrical production
is definitely increasing, the past prediction rates indicate that these
figures may very well be conservative. The energy used to supply this
power in 1970, was falling water (hydro-electric), coal, oil, natural, gas
and nuclear energy. To produce this power for 1990 it will be necessary
to utilize the same energy supply that produced our electrical power in
1970.
Nuclear energy, beset with many problems, has been decreasing in popu-
larity with the electric utility companies. Higher construction cost,
public concern over the potential hazard of a nuclear power plant, and
the failure to develop technological improvements (such as the breeder
reactor) are all given as causes for this decrease in popularity. At
the end of 1969, the FPC reports only 4 million kilowatts of nuclear
generation were in commerical operation and 69 million kilowatts were
under construction or on order. To meet the future load growth, the
breeder reactors that would use 80% of the potential energy in uranuim
fuel instead of the present 1% used by today's reactors, will be needed.
However, the research on breeder reactors has not progressed as originally
anticipated and they may not be available for use until at least sometime
in the 1990's if they in fact become a reality.
The use of natural gas and oil for electric generation is only one of the
many uses found for these fossil fuels. Natural gas and oil provide
approximately 75% of the total energy used by this Nation. Because of the
National dependence on these energy sources, we must be concerned with
their total impact on energy and not just electrical power generation
(although 35% of the Nation's electrical production was supplied by oil
and natural gas). The cause of this concern is the low level of estimated
reserves of natural gas and oil. In the 1970 FPC annual report the Nation's
nautral gas reserves/product!on (R/P) ratio is reported as 13.3 for 1969,
a decline of 10.1% from the 1968 ratio of 14.8. This National' ratio is
the measure of the gas industries annual working inventory of natural gas
divided by the annual consumption rate. This ratio has been steadily de-
clining from 26.9 for 1950 to its present 13.3 for 1969. Additionally, it
is predicted that the R/P ratio in 1973 will be 10.2.
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Unfortunately, the Nation's crude oil recoverable reserves, assuming
maximum recovery and present growth rates, indicate similar concern.
Present estimates for the complete depletion of the Nation's crude oil
reserves ranges from about the year 1990 to 2000. Fortunately, this
energy source can be augmented by oil shale and foreign reserves (which
should extend this energy source beyond the year 2000).
The remaining source, other than coal, is falling water (hydroelectric).
Additional hydroelectric power in many areas of the United States is
unavailable simply because there aren't many rivers left that can be
developed. Hydroelectric power accounts for only some 4% of the Nation's
total energy.
Electricity produced by coal in 1970, was 709.1 billion kwh or almost
half of the electricity produced in the Nation. To produce this electricity
322 million tons of coal were burned. (Total coal mined in 1970 was about
590 million tons). Unlike, other energy sources, the technology needed
to produce electricity from coal is available and the remaining coal re-
serves represent about two thirds of the total energy reserves. Present
proven U. S. coal reserves, mineable at near present cost, are estimated
to last nearly 800 years at todays consumption rates.
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Environment or Energy
As now practiced, surface mining causes severe environmental degradation.
Where surface mining is practiced with total disregard to the environment,
utter and total devastation generally occurs to the land and surrounding
waters. Unfortunately, even when environmental safeguards are considered
the effects of surface mining on the environment are substantial.
With the present surface mining and reclamation technology the prospects
are for only slight improvement in environmental quality. Much research
is needed into surface mining methods and procedures before any sub-
stantive improvement can be expected. Additionally, technology is needed
in applying reclamation techniques that will allow the land to be returned
to its original condition. Present methods of reclamation at best are
only implemented to comply with such minimum stan'dards that exist.
The Nation's ever increasing need for energy is well documented and this
need for energy will in turn increase the demand for coal. Coal is the
only proven energy source that can supply the Nation's electrical power
demands now and into the far distant future as the known supply of coal
is substantially greater than all other useable energy sources.
Surface mined coal, much of which is "steam coal" quality, rather than
"metallurgical" quality, fills about 50% of the Nation's coal requirement.
Therefore, most of this steam coal is being used to produce electricity;
about 25% of the Nation's electrical power is produced from surface mined
coal. Banning or even severely restricting surface mining of coal could
have serious and drastic consequences on the Nation's capabilities to
generate electricity.
The capability to generate enough electricity to meet the Nation's in-
creasing demands has so far been possible. Occassionally, however, an
increased peak demand, such as caused by thousands of overloaded air
conditioners on a hot summer day, coupled with an equipment failure can
cause unbelieveable chaotic conditions. The New York City "black-out"
in mid - 1967, is a classic example of what can happen when a city and
her people, dependent on electricity, have it suddenly and completely
turned off.
The day of this black-out was a warm late spring day. The weather was
clear and very warm. More and more windowless office buildings, apart-
ments, homes and factories increased their demand for electricity. As
the New York City demand increased, electrical power was brought in from
generating stations far away, over an elaborate grid system's transmission
lines. Suddenly a switching unit failed and no electric power was avail-
able in New York City- Mr conditioners, factory machines, gas station
pumps, traffic lights, elevators, lights, trains, and many other electrically
powered devices stopped. The City of New York literally ground to a halt.
Railroads, buses, cars and subways could not move into, out of, or within
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the City. Most people were only inconvenienced, unfortunately however,
some suffered severely. The time of day and the time of year this black-
out occurred probably prevented much more serious consequences to the
City and its people.
The chaotic conditions that occurred in New York City are will remembered
by those who were there. This situation could be repeated if surfaced
mined coal was unavailable and already overloaded systems would strain to
produce demanded electricity as a sudden peak load. Without surfaced mined
coal to help supply the Nation's electric energy these black-outs could
become reoccurring realities.
Continued surface mining of the coal necessary to produce the electrical
energies demanded by the Nation will continue to degrade the environment.
Since other forms of energy are immediately exhaustable or at present,
limited by technology, the coal produced by surface mining is vital to
the Nation's supply of electricity. Therefore, the unavoidable environ-
mental degradation must be carefully balanced against the Nation's
economic welfare and, in fact, its very existence.
The existing practices of surface mining coal seriously affect our environ-
ment. However, it is also recognized that we need the energy that this
surface mined coal can produce for the Nation. It is evident a new alter-
native for extracting those coals presently surface mined is needed.
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Alternatives to Conventional Surface Mining
Much of the coal mined in the United States today is extracted from the
earth using underground mining methods. Tunneling into the earth to re-
move the coal can be done by several methods. Todays modern underground
coal mine no longer uses horse drawn carts and men with picks and shovels
to extract the coal but rather employs modern mining equipment, such as
continuous miners that literally chew the coal from the earth and auto-
matically load it into shuttle cars. Today seven men produce as much coal
as one hundred men with picks and shovels could only a generation ago.
Another method, recently adopted from European practice, is called long-
wall mining. This mining system is further increasing the underground
coal production rates. These mining methods are able to extract the coal
from the earth with less obvious environmental impacts than surface mining.
While underground mining methods may cause less obvious environmental de-
gradation than surface mining, other more favorable considerations influence
the decision to surface mine. For example, the costs of developing a deep
underground coal mine are often quite high and may require 3 to 5 years to
reach full production. It is not uncommon for an underground mine and its
necessary support facilities (i.e. preparation plant, offices, portals, etc.)
to cost well over 20 million dollars exclusive of coal and land costs. The
necessary capital outlay for surface mining, however, can usually be accom-
plished for considerably less money. Many active strip mines are in operation
at less than one tenth of the initial capital outlay required for a comparable
deep underground coal mine.
While there are definite economic incentives for surface mining over under-
ground mining, there are also technological problems that prohibit deep
mining methods from extracting much of the surface mined coal. Shallow
cover coal, where the overburden is relatively thin, provides a very poor
"roof" for a coal mine. This poor roof is detrimental to the safety of men
and equipment. In a recent issue of "Mining Engineering", the publication
of the Society of Mining Engineers, roof failures in underground coal mines
are given as the greatest causes of accidents in coal mining. Poor roof
in a mine increases the probability of dangerously severe and often fatal
accidents. The very plastic and fluid type roofs normally found over
shallow cover coals place severe limitation on the safe recovery of coal.
This is a most important reason for not using conventional underground
mining methods.
Additonally, much of the coal presently surface mined lies in relatively
thin seams. Seam thickness of twenty-eight inches or less are not uncommon.
With thin seam coal and the inherent poor roof a very difficult underground
operation results. The poor roof requires that more supporting coal pillars
be left and the mineable coal, or the coal actually recovered, could be
well below fifty percent. Therefore, to mine small pockets of thin seam
coal with poor roof would not be technically or economically feasible using
conventional underground methods.
Estimates vary between 45 to 130 billion tons of coal mineable using present
surface mining practices. West Virginia alone has an estimated 58 billion
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tons of coal reserves with approximately one-fifth recoverable only by
surface mining. If surface mining was banned, or severely restricted, it
is probable that much of this coal could not be recovered utilizing present
conventional underground mining operations.
Since it would be difficult for present underground mining methods to
recover this large reserve of coal, consideration should be given to the
alternative of full restoration of surfaced mined areas. Careful removal
of the existing top soil and each layer of earth strata will insure that
minimal pollution will result, provided of course, it is carefully returned
in the same manner and position it was removed. Obviously, this restoration
would be completed within days bf the coal removal. By careful revegetation
of a substantial ground cover the land can then be returned to almost the
original contour and vegetation it held before the coal was removed. Thus
full and complete restoration would allow the coal to be removed, returning
the land to almost the same state it. existed in before the coal was taken.
The most significant change taking place being only a slight lowering of the
land and its contours a depth equal to the coal seam thickness.
Minimal environmental destruction will occur when full and complete res-
toration of the surface mined land immediately after the mineral has been
removed, is practiced. The actual mining operations of course being planned
to distrub only small land areas at any one time. Additionally, the size of
equipment and method of operation will be reduced to be compatable with
minimum surface disturbance. Surface mining practiced in this manner should
eliminate much of the harmful effects of present surface mining practices.
Full and complete restoration of the surface mined land will create minimal
environmental degradation. The scarred land with its long term water pol-
ution from sediment and acid mine drainage would not be left behind after
the coal is mined to cause problems that the Nation now is faced with;
However, the full restoration that would be necessary to remove this coal
without these harmful effects would be very expensive, if indeed always
possible. While definitely minimizing and possibly eliminating the long
term effects of environmental degradation that surface mining practices
generally cause, the cost wbuld be exceedingly high. These practices
would prevent much of the present environmental degradation but at a very
Substantial increase in the cost of energy.
Although possible alternatives exist for recovering this coal without the
present total environmental destruction,, new technology needs to be developed
and demonstrated that more effectively and efficiently supplies the coal
necessary to satisfy the Nation's energy needs. Another alternative that
is now suggested may Satisfy the environmental criteria and also supply the
Nation with needed coal energy. It would utilize an underground mining
method recently adopted in this country while exposing only a relatively
small area of the earth. It would protect the environment and supply the
coal needed for the Nation.
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A Proposed New Surface Mining Method - "Longwall Stripping"
The mining of shallow cover coal is necessary and vital to the Nation.
Air, water and land - the environment - is also necessary and vital to
the Nation. To provide the Nation the means, to extract shallow cover coal
while protecting the environment, a new surface mining system is proposed -
"Longwall Stripping".
Longwall Stripping is a method employing the underground mining system
successfully used in European countries for many years. In the early 1960's
this method was successfully adapted for underground coal mines in the
United States. In 1970, there were 30 longwall mining systems operating
or available for operation in the United States. One of these systems in
Pennsylvania mined 7,280 tons of coal in a 24 hour period, a very high pro-
duction rate. The continued future of this mining method in U.S. coal
mines appears certain.
A longwall mining system consists of a series of basic components that are
used in combination to mine coal. The coal is severed from the coal seam
by a cutter, usually called a "plow" or a "shearer", passing over the coal
"face". The severed coal falls onto an "armored chain conveyor" and is
moved from the working face for transport out of the mine. Roof supports
or "jacks" are used along the, full length of the working face to support
the roof while mining is in progress. These jacks can be equipped with
conveyor shifting rams that will move the armored chain conveyor forward
as the plow or shearer passes and also move the jacks forward as the coal
is removed.
The actual severing of the coal in a longwall mining system is by one of
two devices. The coal plow is a sort of wedge shaped shoe that is pulled
along the coal face literally plowing the coal down, .A shearer is a drum
shaped device with hardened metal bits that revolves and chews into the
coal. Both devices cause the coal to fall on to a conveyor parallel to
the working face to be transported to the end of the working face or panel
for further transportation out of the mine.
The roof support system of jacks is able to support tremendous depths of
overburden. These jacks are able to support areas that have a very weak
roof allowing otherwise hazardous areas to be mined safely. These jacks
can be self-advancing to move forward as the plow or shearer passes.
Additionally, they can also push forward the face conveyor that transports
the mined coal from the face. These supporting jacks, as they move forward,
allow the roof to collapse behind the jacks (in the "gob area") eliminating
many of the voids and openings normally found in a mined out area. These
already developed and proven roof supporting jacks could readily be applied
to mining shallow cover coal and are possibly the most significant component
of the system.
Longwall Stripping would utilize existing longwall equipment inserted into
the coal seam. The opening of the earth's surface need only be large
enough to allow the equipment to be inserted, then quickly covered and
completely restored. The only other surface land that would be disturbed
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would be a small traveling opening to remove the mined coal that would also
be quickly covered and completely restored as the miner passed. Thus when
the mine was operating at full production only a smai1. surface land area
(about 100 feet), would be disturbed at any one time.
Longwall Stripping is actually a very simple concept. First a small trench
is opened. This trench would not be much bigger than trenches that are
presently used for large sewer lines. The coal is then removed and the
longwall mining equipment inserted into the coal seam. Prependicular to
and at the "outby" end of this trench, a second opening is started. This
opening allows the mined coal to be removed and also acts as a dike to
prevent water from draining out of the mining area. As the mining proceeds,
and the face advances, this outby opening also advances. Once the face has
advanced sufficiently, the original trench, opened for the inserting of the
longwall mining equipment, can now be backfilled and completely restored. The
outby opening advancing with the longwall mining system is also back-filled
as the system advances. Because of the very small land surface disturbed,
this opening can have nearly immediate and total restoration.
The recovery of shallow cover coal by Longwall Stripping offers many advan-
tages to both the environment and the mining industry. Since little surface
land need be disturbed and full seam mining can be practiced, virtually all
the coal can be recovered. This benefits both the environment and the
operator. The free-flowing property of the plastic roof should cause the
roof to simply flow behind the jacks preventing many of the voids and
openings, normally found in underground mines. Eliminating under ground
voids and openings prevents the formation of water drainage channels that
allow acid waters to flow long after mining has ceased. Additionally, this
immediate and complete joining of the roof and floor will eliminate most of
the subsidence of surface land that commonly occurs from underground mines
as pillers and timber supports deteriorate due to age and surface activities.
Longwall Stripping simply lowers the elevation of the land by the thickness
of the coal seam.
The economics of Longwall Stripping also appear to offer advantages over
present surface mining methods. Obviously, the virtually 100% coal re-
covery from the coal seam is an economic incentive. The capital cost of
the surface equipment (2 or 3 small sized piees for the minor amount of
earth moving involved) would be relatively inexpensive. The longwall
mining system itself consisting of standard "off-the-shelf" equipment with
little, if any, modification required should far exceed present surface
mining production rates at equivalent capital investment. Additionally,
several ancillary benefits that are part of the overall system could add
a considerable economic edge to this new mining method.
The ability of the longwall mining system to operate remotely offers an
ancillary benefit that would substantially increase the safety of the
underground coal miner. While mining the coal using the Longwall Stripping
method no men are needed underground. The miner operates the system from a
totally enclosed cab located outside the mine. When maintenance and adjust-
ments are necessary, the system is completely shutdown. The miner can then
safely go in to observe or maintain and repair as necessary. While in the
mine he would work safely under the jacks supporting the roof. These jacks
are presently supporting many hundreds of feet of earth and rock in under-
ground mines and are considered by the mining industry as the safest known
roof support.
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The environmental benefits of this mining method are substantive. First,
the complete and total recovery of the coal with its subsequent lowering
of the overlain strata eliminates most if not all the voids and openings
for water drainage. Second, only a small land area need be disturbed for
mining the coal. Full restoration of the disturbed land area can then be
easily accomplished. ' Third, the trench used for coal removal, when mining
"up slope", would also prevent acid water from draining into nearby streams.
Any water in the mine would be promptly removed, and treated if necessary,
prior to releasing it to nearby streams.
This type or method of mining can be used in almost all areas that are
presently being surfaced mined. For example, on a typical contour mining
situation where surface mining normally removes the coal along the edge of
a ridge, Longwall Stripping could bfe utilized efficiently and economically.
As another example, this new mining method would be applicable on the
"plains" ("area mining") where the land surface is reasonably flat. Here,
however, the procedure used is slightly different. Two longwall mining
systems extending outward (at right angles) from a center (advancing)
trench are used. They mine in a direction parallel to the initial (starting)
trench perpendicular to the center trench. The center advancing trench
is the operating trench and is where the coal is removed.
The use of Longwall Stripping in area mining can have a significant impact
on coal production and surface mining. Additionally, it is quite probable
that new equipment will be developed for use in a Longwall Stripping system
for shallow cover coal. Second and subsequent generations of equipment
could substantially increase production, efficiency and economics while
continuing to protect the environment from destruction.
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Proposed Demonstration Project
Longwall Stripping offers the Nation the opportunity to recover much
needed energy, coal, while protecting the environment-air, water and
land. No other surface mining method, presently practiced or proposed,
can offer the balance between energy and the environment. To demonstrate
that Longwall Stripping can in fact provide this balance, it is proposed
that a small project be undertaken that will document the advantages -
both environmental and economic.
The demonstration project proposed would be a modest one, requiring less
than 100 acres of a 3 to 4 ft. coal seam. This small project would be
conducted within the constraints of present mining laws, existing equip-
ment design and obviously, the^ geographical and topographical conditions
of the selected site.
In any initial installation of new technology, existing constraints and
site conditions will dictate certain methods and procedures to be followed.
For this discussion of the proposed demonstration project, those constraints
that are known will be used, all others will be assumed. In either case
these constraints will be identified.
The initial application of this new mining concept could be most anywhere
that a sufficient coal reserve existed. Since only a modest demonstration
project is proposed, about 100 acres of a 4 ft. coal seam will be assumed.
Additionally, it will also be assumed that this coal reserve will be in a
continous strip about 200 fit. wide, such as often found in "contour strip
mining".
The site selection, coal reserve and seam thickness, are the basic
assumption. With these assumptions made the development of the proposed
mine can now be discussed. The first step is to determine the most advan-
tageous place to start mining that allows for maximum travel advance. For
example, the strip of coal on this assumed site, approximately 200 ft.
wide, could have the starting point at either end, with the longwall
mining system advancing as a continuous 200 ft. face towards the opposite
end.
The placing of the longwall system would be relatively simple. A trench
is cut at the starting end of the strip, wide enough to allow the coal to
be removed and the longwall mining system inserted. The earth removed for
this trench would be carefully segregated (i.e. topsoil, rock, clay, etc.)
to allow easy return for complete restoration. Once the longwall system
has advanced into the coal seam this trench is then backfilled and vegeta-
tion completely restored.
Perpendicular to this starting trench an advancing trench is cut. This
opening to the longwall mining system will advance with the face and will
be the entry to servicing the equipment and for removing the mined coal.
The trench is excavated in such a manner to allow the complete restoration
of the land immediately after the longwall system has passed. Additionally,
this trench also acts to prevent acid water from draining from the mine
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Into nearby streams. Should there be harmful drainage this trench could
be used to treat this water prior to its release to a receiving stream.
The longwall mining system used for this demonstration will have the same
components used in today's underground coal mines. All components making
up this longwall system are standard designed equipment available from
several U. S. mining equipment suppliers. Although some of this equip-
ment could be modified and redesigned for Longwall Stripping, for this
first demonstration project only equipment already proven in U. S. coal
mines will be used. While the actual site and coal seam will determine
the exact specifications required for the longwall mining system equipment,
the basic components can be selected based on the previous criteria es-
tablished for the proposed demonstration project.
The mining of coal in a longwall mining system is done with a "shearer"
or a "plow". The shearer cuts the coal with a moveable powered arm. This
arm has a head with spaced bits, like small picks, that rotates into the
coal causing the coal to be severed from the seam. The plow is pulled back
and forth across the face of the coal shearing the coal from the seam with
its many pointed edge. Because of the shearer's moveable powered arm it
should be more versatile than the plow for trimming and cleaning the inside
("inby") and outside ("outby") ends of the face. Additionally, it can be
used more easily for full seam mining where slate and rock would have to
be removed. Since the plow would not be as versatile as the shearer in the
initial mine without special redesign, the shearer is the obvious choice as
the "coal cutter" for this first mine.
The remainder of the longwall mining system for this first Longwall Stripping
mine is also available as off-the-shelf equipment. Additional basic components
of the longwall system - the remote control, self - advancing jacks for the
roof support that, while over-designed for shallow cover coal, will provide
maximum safety for the equipment and maintenance men; the armored chain
conveyor that moves the coal mined by the shearer to the outside for
loading on surface transportation; and the dozer plate ("rabbit") for
pushing the mined coal onto the armored chain conveyor - will also be
utilized in this demonstration mine. Other components required such as
cable handler, tube guides, spill plates, etc. that make the total
engineered "package" of a longwall mining system is presently available
from several mining equipment suppliers in the United States.
The next consideration in this demonstration mine is the operating face.
Because of the present underground ventilation requirements this face will
be limited to an initial 200 feet. This ventilation requirement constraint
is why the approximate width of the site selected is 200 feet. However,
this 200 foot face should adequately prove the concept. It is rather
obvious that future mining utilizing this system can mine considerably
longer faces.
Because of the short 200 ft face, the periodic inspection and maintenance
required can utilize a simple industrial type exhaust system for ventilation.
This ventilation system is similiar to those installed in many industries.
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By using a flexible ducting and a modest hood design, the mine air could be
rapidly evacuated when it was necessary for personnel to go inside. However,
while the actual mining is in progress no one is underground and all inspec-
tion, maintence and repair is performed only when the shearer is not in
operation. Additionally, this ventilation system could be so designed to
allow observation during the actual mining operation using a closed circuit
television system and the necessary lighting. This would be accomplished by
fixing the ventilating system to provided continuous ventilation to the
working face, exhausting the dust to a dust collector located outside
the mine.
The operation of the above system, located completly underground, will be
from an instrumented, climate controlled, operator's cab. This cab,
located in the advancing trench at the outby end of the working face,
travels along the cut guiding the mining operation. This control cab
provides a "total environment" for the miner while he operates the under-
ground longwall system from the safety of the operator's cab.
As the coal is mined and conveyed out of the mine, the operator from his
cab can control its flow onto a belt conveyor for transfer to the surface
loading point. Both the load-out point and transfer point can be observed
by the operator and are so designed to be moved as the mining progresses.
Also included in the traveling area of the advancing trench and necessarily
coupled to the operators control center, is the power center required for
the longwall system. The power center supplies electrical power to operate
the system. Electrical power ±s the only utility required since all equip-
ment for this mine are electrically driven.
Advancing ahead of the working face, on land, is the earth moving equipment
required to excavated the advancing trench. Because the trench is small
the earth moving equipment is minimal. The equipment needed would be a
three to five cubic yard dragline, or shovel, a bulldozer, coal transfer
belt, coal storage bin and a means for coal haulage such as a belt conveyor
or trucks. Because of these few pieces of earth moving equipment, the
longwall mining system and the few support items required, this proposed
demonstration projects inital capital cost are modest.
The advancing trench that moves with the operating face is relatively small
and is not at any great depth. This small trench, and the correspondingly
small amount of material disturbed, allows the efficient and effective
restoration of the disturbed area. Additionally, this trench is refilled,
recontoured and revegetated as quickly as the face has passed.
The relatively small amount of vegetative cover removed when the trench
was opened requires a minimum of time and expense to replace. Because of
this small area disturbed and the restoration quickly practiced, the environ-
mental degradation usually caused by present surface mining operations
should not occur.
The obvious benefits resulting from this new surface mining method are sub-
stantive. The ability to mine shallow cover coal without degrading and
destroying the environment will provide the Nation much needed energy at
a reasonable cost. The surface land disturbed has full and complete re-
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storation within days after the earth is opened and exposed to the elements.
This precludes the environmental distruction that often occurs with many
surface mines. Coupled with this minimum surface land disturbance, the
use of full seam mining will eliminate much of the future land subsidence,
voids that provide water drainage channels and the sulfuritic and other
material that produces harmful drainage. This new mining method will
protect the environment yet permit the economic recovery of the coal.
Longwall Stripping offers an answer to the Nation's need to balance energy
and the environment. This is the purpose of this new mining method.
However, an ancillary benefit to the health and safety of the Nation's
miners is worth considering. This system requires no men underground
while mining. The coal is mined with the miner outside the mine away
from the dust, explosions and fire hazards that make coal mining one of
the most dangerous industries in the United States. Additionally, the
miner need only go "inside" when the shearer is not running and he would
be protected by the roof support system that is considered to be the
safest available in the mining industry. When it is considered that the
present underground coal miner has about one chance in ten of being in-
volved in a serious or fatal accident this ancillary benefit becomes
very significant.
In summary the mining system proposed is simply one of a marriage of under-
ground technology with surface mining techniques that provides a peaceful
coexistence, or balance, between energy, coal mining, and the environment,
air, water and land. The recovery of coal, the natural resource so vitally
needed for our Nation's energy requirements, can be accomplished economically,
if not in fact, more econcomically than present surface mining practices.
The Nation needs energy to grow and prosper. Coal can provide this energy.
The Nation also needs the environment - air, water and land - to exist.
Longwall Stripping can provide the Nation energy without destroying the
environment. The trade of a mineral resource, coal, for other natural
resources, land, water and air, can become a practice of the past.
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Appendix B is the report of visits to European mines and mining
equipment manufacturers to learn their advanced technology on long-
wall mining systems.
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May 21, 1973
A Report on a Visit of Three U.S. Mining Engineers to England, France & Germany
by John J. Mulhern, Environmental Protection Agency
Henry F. Moomau, Potomac Engineering & Surveying Co.
Joseph W. Leonard, West Virginia University
This report covers a visit to mining equipment manufacturers
and mines in England, France and Germany to obtain the information
necessary to complete work on a contract entitled "Feasibility Study
for a New Surface Mining Method," often called "longwall stripping."
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"Longwall stripping" is a surface mining method that minimizes
the environmental disturbance often caused by conventional surface
mining. Utilizing longwall stripping the surface need not be com-
pletely overturned, such as in conventional strip mining, nor wasting
of coal or drainage tunnels, as in auger mining. This new surface
mining method simply utilizes a longwall mining system, as currently
practiced in some U.S. deep mines and extensively practiced in European
coal mines, that is adapted for shallow cover conditions normally
surface mined.
To illustrate how longwall stripping works, assume a steep slope
hill area where the coal outcrops along the edge of the hill. Inside
this coal outcrop a narrow "bench" is cut from the surface down to
the bottom of the coal seam. A 15 or 20 foot strip of coal along the
outcrop is allowed to remain that will act as a barrier for any water
drainage and allow a continuous contour line to be established thereby
preventing sediment and landslide problems. Assume the 15 to 20 ft.
strip of outcrop is lying to the west with the coal and hillside to
the east. From this narrow "bench" which is called the "outby" or
"fresh air side" a narrow entry is driven for insertion of the long-
wall mining system. This is perpendicular to the bench and in a direct
easterly lie. This coal "face," for the demonstration mine approximately
250 feet in length, will travel perpendicularly to the bench in a
northerly direction. The coal cutter, called a "shearer" will cut the
coal allowing the coal to fall onto an armored conveyor which is
pushed forward by the roof supporting system called "chocks." As the
entire coal seam is removed one of two mining methods behind the chocks
will be used. One is called "caving" which simply allows the earth
strata to fall behind the chock as the chocks advance. This will
cause immediate subsidence of approximately 50 to 70% the height
of the coal seam. Within about a year the consolidation of the'material
caved should be such that normal surface activities could be carried
out with little if any chance of further subsidence. The other method
would be "stowing" which utilizes a material such as fly ash to be
pneumatically placed behind the chocks causing the strata to be sup-
ported so no subsidence should occur. An additional feature of
stowing, with such material as an alkaline fly ash, is the barrier
affect preventing any future acid mine drainage problem from the area.
Although much of this concept is being practiced in Europe the
fresh air or outby side makes this concept unique in the world. This
is because U.S. coal measures are decidely different than those remain-
ing in Europe.
It is estimated that 1,000 tons of coal per shift per 250 ft.
face can be mined from a seam of about 52 inches. Although the potential
is there to mine this coal without miners at the coal face while the
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shearer is cutting coal, the first mine will probably have three men
inside but under massive shield-type chocks with remote control panels
allowing them to operate the shearer, conveyor and chocks from the
protection of these shields. Unfortunately the technology that exists
in automating longwall mining systems is not available in the U.S.
The following is the day to day account of the visit to England,
France and Germany.
February 28. 1973 - Visit to England
Discussions were held at Lancashire, England, with William
Higgins, Export Sales Executive; Les Aarnot, Sales Manager; and
Alan Purdy, Managing Director-Export, Gullick-Dobson Company
Limited (Represented in the U.S. by Joy Manufacturing Co.). Three
films produced by the National Coal Board and one film produced by
the Gullick-Dobson Company were presented concerning automated
longwall strata control and longwalling support systems. Following
the films, a general discussion on longwall mining, longwall support
systems (chocks), and the general concept of'longwall stripping was
held.
From these discussions, we gathered much information on the
state-of-the-art of roof control and roof support practice throughout
the world. It was generally agreed that the major problem with the
longwall stripping concept was the outby side.
After a lengthy discussion with an exchange of ideas on mine
roof control and coal cutting, the meeting was adjourned until
the next day.
March 1. 1973
We returned to the Gullick plant to meet with Mr. James
Anderson, Consultant to Gullick, who was formally the Chairman
of the Northwestern Region of the National Coal Board and the
inventor of the coal shearer used in longwall mining. Also
present were Messrs. Purdy, Aarnot and Higgins.
The discussion focused on problems encountered in longwall
mining of coal under shallow cover. It was suggested that there
were several ways to manage the outby problem, a few of which
follow: 1) packwalling behind the chocks closest to the outby
side using material taken from the excavation; 2) cribbing with
concrete blocks; 3) a specially designed chock on the outby side
that would also act as a shield; 4) bolting with resin bolts and
wire mesh or with resin bolts and metal plate strips to bind the
overburden in place.
51
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Additionally, other points discussed were: 1) consolidation
from subsidence would be approximately 50% of the seam thickness;
2) after twelve months, material would be completely consolidated
so that normal surface activities could occur without further
subsidence; 3) the mined out area would probably be completely
sealed eliminating drainage after mining; 4) a shearer offers the
only practical means of off-the-shelf equipment for "coal getting;"
5) the entire system could (at considerable expense) be remotely
controlled so that men would not be needed underground during
operation.
At the conclusion of the visit, new developments were
observed in an area of the Gullick plant used for applied
research, development and special testing. They demonstrated
their remotely controlled chocks, which they were in the' process
of final testing, for application in longwall mining.
Mr. Jim Francis, Chairman of the Gullick-Dobson Mining
Group, was also interviewed. Mr. Francis discussed problems
encountered in American mining operations. He stated that
Gullick is interested in the concept of longwall strip mining
and would provide engineering and roof control expertise
wherever possible.
The following conclusions were reached after visiting
Gullick: 1) roof control, particularly on the outby side, is
the major critical point in longwall stripping. It is con-
sidered that the roof control inby will not be a particular
problem with thick sandstones. Shales would be the next ideal
roof; 2) the outby side can be supported with a specially
designed chock which would be guaranteed by Gullick; 3) Mr. Alan
Purdy, a Mining Engineer and Managing- Brector of Export, has
experience and considerable knowledge about longwall mining of
coal under shallow cover; 4) using the "caving" system of long-
walling, recovery of coal under shallow cover is possible and
only in rare instance would it be impractical; 5) American long-
wall mining technology seriously lags behind British and European
technology. However, this is probably because of the different
mining conditions and their exhaustion of the easy to mine coals
in Europe; 6) our application of longwall stripping in a demon-
stration mine would be the first ever attempted.
March 2, 1973 - Visit to the National Coal Board
We visited with Mr. A. M. Clark, Deputy Chief Geologist of
the National Coal Board. Discussions concerned the limitations
of the "pressure arch theory", which is advanced by many theorists.
Although some serious exceptions to the theory have been noted in
recent years, it is still considered reliable.
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4
Subsidence problems associated with longwall mining or caving
of the material behind the face were also discussed. In certain
mining situations, the British have special expertise and under-
standably lead American technology.
Mr. Clark was helpful in pointing out differences between
British and American coal mines. As a geologist, his discussion
was concerned with strata control at the great depths typical
Of British mines. Since British mines are much deeper than
American mines, strata control frequently is achieved with
techniques not commonly in use in America. Hence, in trying
to adopt European technology directly to American mining con-
ditions we must be careful in our understanding of these con-
ditions.
To Mr. Clark's knowledge, longwall mining with the outby
side in "fresh air" had not been tried before. He believed that
the system is feasible. Moreover, he believed this system would
prove practical and result in a significant advancement in mining
technology.
Mr. Clark made several other points of interest: 1) surface
mining ("open cast") of coal in England amounts to about 10% of
total coal production; 2) it is about one-third as expensive to
open cast mine in England than deep mining; 3) deep mining pro-
duction averages about four tons per man; 4) reclamation costs
were estimated to be about 25% of the cost of surface mining.
Mr. Clark recommended a visit to the Royal School of Mines.
However, he did not think they could add much to what was already
known since they specialized in "hardrock mining." He also
suggested a return visit Monday morning to talk to Mr. Phillip
Weekes the Director-General of Mining of the National Coal Board.
Prior to leaving for the day, arrangements were made for a return
visit with Mr. Weekes.
March 3. 1973
A visit was made to the Royal School of Mines, as suggested
by Mr. Clark. Unfortunately, no one was available for discussion
and this proved to be a meaningless trip.
March 5. 1973
We met with Mr. Phillip 6. Weekes, Director-General of Mining,
National Coal Board. A lengthy discussion was held with Mr. Weekes
concerning the longwall stripping concept. Mr. Weekes advised
that, to his knowledge, the system would be unique because of the
53
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fresh air outby side. It was his opinion that the system should
be "quite successful." We also discussed at length with Mr. Weekes
the use of automated longwall faces for extracting coal. It was
apparent that automated longwall coal mining technology is much
further advanced in Great Britain.
Mr. Weekes is attempting to develop an extensive library
or source of material dealing with coal mining problems through-
out the world. Therefore, the past and present work of the
Environmental Protection Agency was discussed. Mr. Weekes was
provided with a copy of the EPA project book together with the
promise that final reports would be provided to him of projects
he might find of interest.
March 6, 1973 - Visit to French Coal Mine
\ , -.
We met with Messr. Benno Niedzielski, who is the Public
Relations Officer for the French Coal Mining Industry. Messr.
Niedzielski acted as interpreter throughout the visit.
Two coal pits were visited in France; one at Mellebach,
and the other at La Houve. The Mellebach mine will be closed
by 1980 and is presently being pillared out.
The La Houve mine is the largest mine in Europe and is
presently producing 8,000 tons of coal per day using longwall
mining with powered chocks and drum-type shearers. Roof con-
trol problems were evident at the face but good team work by
the miners and good engineering made it possible to keep the
section operating. The coal face was over 100 meters long and
was about 3100 meters below the surface.
As a general rule the mining conditions were more difficult
than those encountered in American mines, and it is a tribute
to the French industry, their engineers and miners that coal is
provided so consistently.
Surface facilities were also visited and, control panels
for monitoring performance were examined. These panels indicate
the percentage of methane, water problems, electrical problems,
maintenance problems, and production problems at all working
faces. Additionally, they observe the process of the tunnel
driving crews to determine what, if any, problems are being
encountered. Should it be necessary, the engineer monitoring
on the surface can communicate with anyone underground.
A discussion was held with Messr. Cariven, the Chief Engineer
of the La Houve mine and his engineers Messr. Bonnet and Messr.
Sauder. Problems common to coal mining were discussed. The
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French appear to be ten to twenty years ahead of our mining tech-
nology. Additionally, a meeting was held with Mr. Grison,
Director, Houilleres du Basin de Lorraine who discussed, through
Messr. Niedzielski, longwall mining and subsidence under shallow
cover.
March 7, 1973 - Visit to German Mining Equipment Manufactures
We visited the Westfaila lunen Company of Lunen, Germany, one
of the major suppliers of longwall mining systems to the United
States. They are represented in the United States by Mining
Progress Inc. The visit to the Westfaila Lunen Company was pre-
viously arranged by Mining Progress.
Meetings were held with Dr. Karl-Martin Zentgraf, New Products
Director and Mr. Johannes E. Laabs, Chief Engineer, Technical Sales
and Production of Westfaila Lunen. Discussions with these gentlemen
lasted for several days, and included a visit to German mines.
The discussion the first day was on our concept, longwall
stripping. Additionally, arrangements were made for our itinerary
in Germany. It was decided that March 7th would be spent at
Westfaila Lunen; March 8th with Eickhoff (manufacturers of
shearers); March 9th with Westfaila (visiting pits) and March llth
reviewing with Westfaila their proposed equipment design for a
longwall strip mine. Also, a tour of the Westfaila manufacturing
facilities was scheduled.
March 8, 1973
We met with Mr. Heinrick Stock, Salesman, and Mr. Otto Renzing,
Chief Design Engineer, Eickhoff. Application of Eickhoff equipment
was the subject of much discussion and much information on coal
cutting was obtained.
An evening meeting was held with Dr. Zentgraf to discuss
Westfaila Lunen's Bischoff Company they recently acquired as a
means to enter into the air and water pollution control market.
Dr. Zentgraf was interested in the knowledge that was made avail-
able to him during the discussion.
March 9. 1973
We again met with Mr. Laabs from Westfaila and with him
visited the West German pits, in particular the Westfailan
Mine. The surface control room, where all underground activity
is monitored, recorded work stoppages, the percentage of methane
and any potential electrical malfunctions. In the event of a
55
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mining accident, the West German Inspectorate had access to all
of these records and could pinpoint the cause with a high degree
of accuracy. The Westfaila "shields" that afford maximum pro-
tection underground from falling roof were also examined at this
mine. These chocks, first conceived by the Russians, appear to
be an excellent roof support system for poor roof conditions.
They are not yet used in the U.S.
March 11. 1973
A detailed discussion was held with Mr. Laabs on Westfaila's
equipment proposal for application in our demonstration mine.
Mr. Laabs felt that this condition was unlike anything in Europe,
because of the fresh air or daylight entry. He believed if roof
control could be achieved at the outby side, a most significant
contribution to coal mining would result.
The system that he proposed appears to be viable. He
believed the proposed system would be economically sound. He
felt that plows might have some application for producing coal
at the longwall face, but it would be necessary to have two outby
areas, which could create difficulties for the first mine.
Mr. Laabs1 initial suggestion included the new Westfaila
shields. Mr. Laabs1 cost estimate for these shields was about
25% more than the standard Westfaila chocks. His longwall system
included a longwall face that would be about 80 meters long,
(approximately 264 feet) with a 25 foot outside extension. His
system also included a coal cutting device, such as a shearer,
and an automated system that could remotely move chocks and
advance the shear with only three men at the face. These men
would remain in position at specially designed chocks (shields).
A fourth man would be on the fresh air side at the end of the
system. Mr. Laabs had, for budget purposes, included lighting,
ventilation, etc. He estimated that a face of about 264 feet
could cost approximately $4,000 a foot, including the 25 foot
outside delivery system.
March 12, 1973
We met with the Becorit Company, Messrs. Walter Lubogatzky,
Director, Technical, Peter Beckmann, Director, Commercial and
Theodor Kolk, Engineer.
, The discussion started with an explanation of longwall
stripping. After the discussion, when the concept was understood,
Becorit produced a film that was made in a German pit about five
years ago, utilizing Becorit chocks, an Eickhoff shearer and a
Westfaila panzer conveyer. This was an automated longwall system
considerably advanced beyond any seen or discussed during our
European visit. After discussing the film and how it related
to our application, the proposed longwall stripping system was
seen as being practical, economical, and safe.
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8
Although Becorit does not have a sales agency or any export
to the United States, the Gullick-Dobson Company which owns 51%
of Becorit does (through Joy Manufacturing Company.) The
Becorit Company requested the privilege of preparing a proposal
for budget,purposes and for the design of the outby supporting
system. Based on their previous experience, they did not under-
stand why coal, mined at shallow depths, should be a problem.
Becorit chocks are different from the Gullick chocks and they
may be more adaptable to American coal measures. The Becorit
Company will send a copy of their film on the automated longwall
mining system.
March 14, 1973 - Visit to the Rheinische Braunkohlenwerke AG
Through the efforts of Mr. David Struthers of the International
Affairs Office of EPA, the American Embassy was contacted in Bonn
where Dr. Clyde McClelland, Scientific Attache, arranged a visit
to Rheinische Braunkohlenwerke (the "Brown Coal Region" of West
Germany). Accompanying us from the Embassy was the Deputy Scientific
Attache, Mr. Alan Hegburg. Mr. Berging H. Maucher, mining engineer
of considerable experience in the Brown Coal 'Region, conducted the
tour. Mr. Jan Kayser, a mining engineer from the Rhein Braun Consulting
Firm, of the same company, was also available for a discussion period.
Several pits were visited which were awesome in size and larger than
any pits in America. These pits furnished brown coal to seven power
plants and six briquette plants. Additionally, three thousand tons
per day of sand and gravel are recovered for sale, together with three
million tons of water per day some of which is sold to local towns
for the water supply. It was expected that since the water quality
was good, the water market would continue to grow.
Several things, besides the size and magnitude of the mine
were of interest. (!) The earth that was being moved was soft
and easy to dig so that no blasting, drilling or other rock shat-
tering procedures were necessary.' (2) At one pit, 600 meters of
material was removed to recover 50 meters of brown coal. (3).A
high degree of good engineering, planning and sound management
was practiced. (4) The power of eminent domain allows them to
acquire all surface land. (5) The people who were displaced from
homes were given the opportunity of choosing a home of higher
value than the one they were displaced from, pay more money to
improve their housing quality, or take money in exchange for a
small home or smaller land acreage. (6) Total resource recovery
was being practiced and the land was returned to a condition that
was equal or better to the previous condition. (7) Good engineering
management, good land use. practices and government-industry coopera-
tion can achieve these same results in America.
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While these findings may not be directly applicable to all of
the coal fields in America, benefits from the technology observed
in the Brown Coal Region can,be utilized to improve our mining
environment technology. "Daylighting" in these regions may merit
further consideration. The Brown Coal area is, without a doubt,
one of the best examples of balancing mineral resource recovery,
"mining" with the "environment."
The above is a report on the information obtained during the
visit to England, France and Germany. Since this visit the infor-
mation required to complete the study has been finalized. Additionally,
a grant application has been received by EPA from the West Virginia
Surface Mining and Reclamation Association to cooperatively demon-
strate "longwall stripping."
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Appendix C is a compilation of the various engineering drawings
that were conceived during the progress of this study.
59
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SELECTED WATER 1. Rer *#<»
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
3 4^ M '" *" '"/(•
w ''"«»
4. Title
Feasibility Study of a New Surface Mining Method
"Longwall Stripping"
5. R- >ortJD;:e
6.
8.
Moomau, H.F., Zachar, F.R. & Leonard, J.W.
Potomac Engineering & Surveying
Petersburg, West Virginia
Rt,,»rtN(.
No.
/?. .'Sponsoring
n U. S. Environmental Protection Agency
C ii'f t "' •! ' Nu.
68-01-0763
13. Type a' Repot- »nd
Period Covered
15
Nates
U.S. Environmental Protection Agency
Report No. 670/2-74-002
Ifi Abstract
"Longwall stripping" is a new surface mining concept developed by the
Environmental Protection Agency. Longwall stripping adapts existing under-
ground longwall mining technology for use in recovering shallow cover coal
without the total environmental disturbance often associated with surface
mining. This study investigated the environmental, mining and economic
feasibility of longwall stripping.
Longwall stripping was determined to be a feasible method for mining
coal under shallow cover. A discussion of the criteria that is necessary
to consider in selecting a site and developing the mining plan is included.
Additionally, alternate methods of the longwall stripping concept are
discussed.
This report was submitted in fulfillment of Contract 68-01-0763 under
the sponsorship of the Office of Research and Development, Environmental
Protection Agency.
17a. Descriptors
^Environmental disturbance, ^Surface mining, *Strip mining, *Auger mining, *Longwall
mining, *Shortwall mining, *0pen-end outby, *Fresh-air outby, *Shallow cover mining,
*Roof-support, *Shearers, *Chocks, ^Conveyors, ^Continuous miner, *Packwalling,
*Bench, *Stowing, *Highwall
17b. Identifiers
Longwall Stripping, Feasibility
17c. COWKK Field & Group
If,. Avjihhitity 19. Security C"3*S.
(Report)
W- Security Class.
f-" 'geJ
*k, ;.»-^ H. F. Moomau
21. V0.0/
Pages
22. Price
Send To :
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON, D C ZO24O
'ns . uv., Potomac Eneineering & Survpy
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