2017-03-21_REVISION - M1981207 - Laserfiche WebLink

Home Browse Search

Blue Pit 112 Permit Amendment Exhibit U - Geotechnical Stability There are no buildings or any structures outside the permit area which could be affected by the excavation. A minimum fifty foot buffer will be maintained from the permit boundary line to all excavations. All reclaimed areas will be restored to relatively flat (<3.5%) slopes except for the side slope, which be mined to a 1.5H:iV and reclaimed to a 3H:iV slope. The surface material of these slopes will be topsoil. During placement of the backfill material, the operator will compact using standard earthmoving techniques. The soil type of the overburden and waste fines used in the backfilling of the side slopes will range from sand -silt -clay with slightly plastic fines to inorganic silts and clayed silts. Design factors The reclamation plan calls for 2 benches of io feet width in a slope height of go feet, therefore, the overall slope will be reduced from 3:1 to 3.1:1. These slopes will also be used to collect runoff from the slope itself and reduce erosion. The 3:1 slope will be backfilled, topsoiled and reclaimed to dry rangeland, as desired by the landowner and required by the DBMS. In the extremely remote case that a slope failure would occur, if the slope failed up to the overhead power line west of the permit area (the closest man made structure to the operation), Figure 4- 502.C(6)A shows the slope angle that would occur. The horizontal distance from the edge of the excavation to the power line is 55 feet. The failure angle would be 20 degrees or 2.7H:1V. This angle is far milder than normal failure angles in material that gets strength from internal angle of friction. Figure 4-502.C(6)B, from Huang, shows typical internal angles of friction for various Aggregates, Inc.. Assuming that the gravel is classified as GC, clayey gravels, poorly graded gravel - sand - clay, this material has an internal angle of friction of approximately 34 degrees. Blue Pit May 2014 U-1