1987-12-01_PERMIT FILE - C1981017 ‎(289)‎

• Permit No: C1981017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 12/1/1987
• Doc Name: Geotechnical Investigations Mine Portal Benches and Haul Roads
• Section_Exhibit Name: Chapter V Appendix V-E-II
• Media Type: D
• Archive: No

2. 3 MINE BENCHES
The five Coal Basin mine benches are located within the
lower part of the Mesaverde Formation, at the outcrop of the
coal seams. Mine benches of mines nos. 1, 3, 4 and 5 are at the
outcrop of the Coal Basin Seam, immediately above the Rollins
Sandstone Member; the mine bench of mine no. 2 is at the
outcrop of the Dutch Creek Seam that is located higher in the
Mesaverde Formation.
All mine benches were constructed in a similar way; a high
cut was excavated above the coal seam outcrop. The elevation of
the cut toe coincides approximately with the bottom of the coal
seam and with the elevation of the mine bench. The excavated
material was deposited in one or more fills.
The mine bench cuts have been excavated either in the
Mesaverde bedrock formation or in col luvial soils. - In either
case , they were excavated at steep slopes , steeper than 45
degrees. Such steep slopes may be appropriate for the bedrock,
but cuts in colluvial slopes may experience some minor
stability problems.
The mine bench fills were constructed in a similar way to
the road fills. The foundations for the fills were not stripped
of vegetation (if any) , topsoil was not removed, and no keying
of the fills into the foundations was applied. Very probably,
the fills were not compacted. The fills can, therefore, be
classified as loosely dumped fills .
The configurations of the fills depend very much on the
topographic conditions of the site (similar to the haul road
fills) . On steep natural slopes, the fill material is spread
out for a large distance below the mine bench elevation. The
"height" of some fills may reach up to 500 feet or more. The
actual thickness of such fills, although not accurately known, ,
is very probably limited to several feet only. Occasionally,
vegetation can be observed protruding through such 'fills.
The material of the fills is a mixture of soils and rocks.
Larger size boulders of sandstone frequently roll down the
slope for a considerable distance. They cover the area below
the toe of the fill .
On flatter slopes , or on slopes where the gradient
decreases downslope , the thickness of the fill may be
considerably larger than on the above described "sliver"-type
fills. Thicker fills may then become a part of the mine bench.
Potential stability problems of these two fill types are
different. Thin, sliver-type fills do not experience serious
stability problems , except for shallow sloughing and locally
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