2014-06-25_REVISION - M1977522 - Laserfiche WebLink

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L.G. Everist, Inc. Permit# M-1977-522 Star Water Resource JUNE 2, 2014 GEOTECHNICAL STABILITY EXHIBIT This information is presented to address the plan to mine within 200 feet of the structures listed in Exhibit S . Mining is completed on areas that were within 200 feet of any structures around the mine. However, a slurry wall installation is planned for the existing lake areas shown on the map. In relation to these slurry walls it will be necessary to create level pads where the slurry walls will be excavated. A slurry wall is typically 3 to 4 feet wide excavated through the gravel deposit into bedrock. This excavation is filled with a bentonite clay and dirt slurry that keeps the walls from collapsing so there is no danger that it will fail and cause damage to structures within 200 feet. During construction of the pad it is necessary to excavate into the existing slope creating a level bench that at its deepest point would be 16 feet below the original slope. The up and down hill edges are then graded 3h: ly to blend with the existing slope. At this site, that means the maximum depth of near vertical highwall is 16 feet high. The closest structure for which there is no damage agreement is "0" Street along the north side of the site. This street at its closest point is 84 . 5 feet from the vertical face. The following information is presented using these distances to determine the safety factors that show there would be no impacts to structures within 200 feet of the permit area. Site information shows that the existing slope is graded at 3: 1 of flatter. The natural angle of repose or friction angle for this gravel deposit is approximately 45 or 1 : 1 . This falls into the parameters listed in Rock Slopes: Design, Excavation and Stabilization, Publication No. FHWA-TS-89-045, Table 1 - Typical Soil and Rock Properties for Sand and Gravel, mixed grain size. This