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STATE OF COLOR4D0 piCN Mn Gove~~or <br />~ iii iiiiiiiiniiiiii <br />r y~i <br />DEPARTMENT OF NATURAL RESOURCES <br />' ~~~ ~ Harris D. Strerman. Executive Director <br />. MIlVED LAND RECLAMATION <br />723 Centennial Building, 1313 Sherman Street <br />~ Denver, Colorado 80203 Tel. (303) 8923567 <br />Hamlet J. Barry, II I, <br />Director <br />May 22, 1980 <br />TO: Rick Mills <br />FROM: Jim Pendleton <br />RE: Recommendatio rassy Creek Coal's Strip Mine Haul Road <br />Slope Stability Problem <br />Naving examined the site with you Wednesday, May 14th, I offer the following <br />observations and recommendations. Grassy Creek Coal's access road was <br />excavated through a fairly steep dipping section of shales, mudstones, <br />siltstones, sandstones and coals, typical of the coal-bearing mesa verde <br />group's geological formations. The road was constructed by excavating <br />a cut into the steep slopes of the narrow valley. Unfortunately, these <br />rock types are characteristically prone to an assortment of detrimental <br />geological phenomena, such as shrink-swell and liquefaction, which <br />combined to facilitate numerous slope failures. In situations such as <br />this, the best cure is avoiding the problem. Unfortunately, the damage <br />has already been done in this particular situation. The unusually wet <br />winter and spring we have just experienced has caused slope instability <br />to be manifested throughout much of the haul road length. <br />The initial response of most individuals to a slope failure of this nature <br />is to remove the failed material and cut the slope back, increasing the <br />height of the upslope cut. This is for all practical purposes, the worst <br />action that can be taken, encouraging ever-increasing disruption of the <br />cut slope. Ideally, the solution to the slope problem is to replace the <br />retention which was removed when the slope was cut. This can be done <br />by installing retaining structures, but is probably prohibitively expensive <br />in a haul road situation. With this in mind, what practical and economically <br />feasible alternatives are available to the permittee? <br />1) Durable rock buttresses could be placid against the slope in the <br />areas of failure. The operator could expeditiously excavate the , <br />failed material and replace it with sandstone boulders. The high <br />density of the sandstone will assist in replacing the weight <br />originally removed during excavation, retaining the weaker rocks <br />of the cut slope. Culverts may have to be installed to allow drainage <br />in those areas where narrow shoulder situation makes it difficult <br />to maintain the appropriate drainage ditch. <br />(cont'd) <br />