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STATE ~ COLORA00 RiC Hnnrt D. Lott M. G„v,: ~„nr III III III III IIII III <br />D ET'ARTMENT OF NATURAL RESOURCES 999 <br />D. Monte Pascoe, Executive Director <br />M1NED LAND RECLAMATION <br />423 Centennial Building, 1313 Sherman Street <br />Denver, Colorado 80203 Tel. (303) 839-3567 <br />David C. Shelton <br />Director <br />M E M O R A N D U M <br />~~~ 9 June 1982 <br />~ '~~\` <br />TO: Dan Mathews ~ '~ i - <br />l-." ~ ~ 1. _ <br />FROM: Jim Pendleton ~''~'"~f~ ~-l <br />~~.•. -- <br />RE: Suggestion f~~~Trea ent of WSC's Portal Face-Up Slope <br />c_ <br />I have pondered the panorama of the West Portal at the Hawk's Nest <br />Mine operated by Western Slope Carbon, Inc. I offer the following <br />observations and suggestions for your and their consideration: <br />(1) The problem appears to be surficial, limited to unsightly and <br />untidy sloughing of debris onto the portal bench. It should be treated, <br />however, or it could degrade with time and produce a more dangerous and <br />costly deeper failure. <br />(2) The slope gradient needs to be lowered to allow some planting or <br />armoring scheme to take hold and prevent the sloughing of the face. <br />There are only two ways this can be accomplished: cut back the head of the slope <br />or extend the toe of the slope. Cutting back the head of the slope is unacceptable <br />because it would greatly increase the disturbed area and because its confined <br />by the presence of the diversion ditch near the head of the existing slope. <br />Extending the toe of the slope eliminates the working portal bench. The only <br />other way to change the effective location of the toe is to install a retaining <br />structure of some sort to mimic a toe buttress. <br />(3) Typical retaining structures used for these purposes consist of concrete <br />retaining walls (expensive), cable anchored "tie-back" walls, binwalZs or <br />cribbed structures. The retaining wall, whatever kind used, should probably <br />extend to several feet above the peak of the portal arches. This will also <br />- provide protection for the bench a.nd its occupants. The wall is then <br />backfilled with course buttress mateziaZ which allows open draining and provides <br />high density buttressing weight for the slope. Finally the slope gradient above <br />the retaining wall is lowered by either installing upper terraces or backfilling <br />the upper slope to a lower gradient. If the upper slope can be reduced to <br />2h:1v it should be possible to stabilize the surface sloughing throughout <br />the planned life of the operation. Following the cessation the retaining <br />structure can probably be~backfilled in place which will assist in stabilizing <br />the final reclaimed portal slope. <br />cc: Dave Shelton <br />Fred Banta <br />