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Mr. Chri Oestreich <br /> September 29, 2023 <br /> Page 3 <br /> acceleration loads were performed. Seismic loading was obtained from the U.S.G.S. Unified Hazard Tool. Review of <br /> the Hazard Tool indicated a maximum horizontal acceleration of 0.091 g with a return period of 2,475 years for the site. <br /> The maximum and most conservative cross section along the L.G. Everist conveyor was analyzed as described below. <br /> ► Section 1: This section is on the north side of the northwest cell and considers the point where the tallest mine <br /> high wall (deepest bedrock, 39 feet)and the thickest overburden (4-feet)is closest to the conveyor. The <br /> conveyor is approximately 29-feet from the mine limit, however the search properties enabled in the Galena <br /> program were for failure circles initiating 10-feet from the structure. Thus circles within 19-feet of the mine limit <br /> were searched. In addition,a 500 pound per square foot(psf)surcharge load was modeled at and near the <br /> conveyor to account for maintenance vehicles servicing the conveyor. The mine highwall in this area will be at <br /> a slope of three horizontal to one vertical (3h:lv). <br /> MATERIAL PROPERTIES <br /> The material index and engineering strengths assumed in this slope stability report are discussed below. <br /> Overburden <br /> The strength properties for the insitu sandy clay to silty sand overburden were based on our engineering judgment;the <br /> following parameters have been used to model the overburden. The overburden is weaker that the underlying sand and <br /> gravel and ranged in thickness from 2 to 5 feet. <br /> Unit Weight Cohesion C'psf Friction Angle <br /> c 010 <br /> 114 50 28 <br /> Alluvial Sand and Gravel <br /> The sand and gravel is generally a fine to medium-grained, locally coarse grained sand locally grading to sandy gravel <br /> and is the thickest unit in the mine highwall. The alluvial sand and gravel was modeled as follows: <br /> Unit Weight Cohesion C'psf Friction Angle V° <br /> c <br /> 129 0 35 <br /> Bedrock <br /> Bedrock below the alluvium is claystone,siltstone, and sandstone that is commonly interbedded and weathered in the <br /> top foot. Sandstone and siltstone are typically stronger than claystone. Claystone is generally a weak bedrock. <br /> Because of the common sandstone and siltstones and the interbedded nature of the bedrock,we modeled the bedrock <br /> as sandy claystone. For the sandy claystone bedrock both weathered and unweathered strength conditions were <br /> considered. Based on the borings at the site,the weathered bedrock was modeled with less cohesion and a slightly <br /> lower friction angle. <br /> Unit Weight(pco Cohesion C'psf Friction Angle V° <br /> Unweathered = Unweathered = Unweathered =29 <br /> 126 100 Weathered =28 <br /> Weathered = 110 1 Weathered =50 <br />