2018-07-10_PERMIT FILE - M2018037 (4)

Home Browse Search

Mr. Mark Johnson May 31, 2018 Page 4 ► Section 7: This section is on the southeast side of the northeast cell and considers the point where the Lupton Bottom Ditch is closest to mine high wall in this cell. The Lupton Bottom Ditch is approximately 96 feet from the mine high wall. ► Section 8: This section is on the north side of the northeast cell at a point with the tallest high wall of the mine. This section considers the Central Weld County Water District water line located on the south side of WCR 14.5. The water line is approximately 82 feet from the mine high wall. MATERIAL PROPERTIES The material index and engineering strengths assumed in this slope stability report are discussed below. Overburden The strength properties for the insitu sandy clay to silty sand overburden were based on our engineering judgment; the following parameters have been used to model the overburden. The overburden is weaker that the underlying sand and gravel and ranged in thickness from 2 to 5 feet. Dry Unit Moist Unit Saturated Unit Cohesion C'psf Friction Angle 0'° Weight(pco Weight(pco Weight c 103 114 126 50 28 Alluvial Sand and Gravel The sand and gravel is generally a fine to medium-grained, locally coarse grained sand locally grading to sandy gravel and is the thickest unit in the mine highwall. The alluvial sand and gravel was modeled as follows: Dry Unit Moist Unit Saturated Unit Cohesion C'psf Friction Angle 0'° Weight(pco Weight(pco Weight c 119 129 130 0 35 Bedrock Bedrock below the alluvium is claystone, siltstone, and sandstone that is commonly interbedded and weathered in the top foot. Sandstone and siltstone are typically stronger than claystone. Claystone is generally a weak bedrock. Because of the common sandstone and siltstones and the interbedded nature of the bedrock, we modeled the bedrock as sandy claystone. For the sandy claystone bedrock both weathered and unweathered strength conditions were considered. Based on the borings at the site,the weathered bedrock was modeled with less cohesion and a slightly lower friction angle. Dry Unit Moist Unit Saturated Unit Weight(pco Weight(pco Weight(pco Cohesion C'psf Friction Angle �'° Unweathered = Unweathered = Unweathered = 116 126 135 _ 100 Unweathered = 29 Weathered = 110 Weathered ea he ed Weathered = 50 Weathered =28 Soil-Bentonite Slurry Wall The proposed slurry wall will consist of a mix of the overburden sandy clay to silty sand, alluvial sand and gravel, bentonite slurry, and imported bentonite. The resulting mix will produce a non-Newtonian fluid with some shear strength characteristics based on a reduced friction angle of the overlying overburden. Based on engineering judgment, we modeled the slurry wall as follows: