_GENERAL DOCUMENTS - C1981017 (216)

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k SECTION 2 - HIGH ROCK CUT, MINE BENCH GENERAL: Excavated in rocks of Mesaverde Formation (sequence of sandstones, siltstones and claystones) . Excavated in steep slopes, generally more than 450. Part of the cut close to the crest may be in colluvial soils. Rocks within this cut portion may be weathered. STABILITY AND OTHER PROBLEMS: As the bedding is horizontal or dips at a flat angle into the mountain, the general (overall) stability is good. No numerical methods are available to calculate factors of safety of the slope (except for cut portions in colluvial soils) . Because of the rock mass nature , and because no controlled blasting methods were used during the cut excavation, the cut surface is rugged, uneven, with loosened blocks on surface. Rock fall is usually important from the cut face. Rock and soil fall from the uppermost cut portion excavated in colluvial soils and weathered rocks may be severe if thickness of this zone is more than 6 - 10 feet; as this zone is usual- ly dry with no possibility of long-term saturation, stab- ility problems are of limited importance. Rock fall material accumulates at the toe of the cut. RECLAMATION CONCEPT. Place a low buttress at toe of cut to increase the cut's long-term stability. Contour the buttress so that if serves as the catching space for the rock fall if any human activities are expected in the vicinity of the cut toe. Flatten the cut portion close to the crest if the total thickness of soils and weathered rocks exceeds 6 feet and if construction of the pioneer road is technical- ly feasible . METHOD OF RECLAMATION. Use material obtained from the fill opposite the rock cut to place a buttress against the cut toe. If material is unavailable, use any source of borrow material in the vicinity. Select the height of the buttress accord- ing to the availability of material. No specific require- ments on compaction of buttress. Contour the buttress according to specifications to act as rock fall protective structure. If construction of a pioneer road to the cut crest is feabsible and flattening of the crest portion is desired , construct a road to cut crest to enable access with a dozer and/or backhoe. Construct road with minimum disturbance. Flatten the slope of the cut portion in soils and/or weathered rock to the flattest slope possible be- tween 45 and 26 degrees (1 : 1 or 2 : 1) . Push material of excavation over the cut crest and use for construction of buttress at the toe as described earlier.