2010-01-21_PERMIT FILE - M2009082 (10)

Home Browse Search

Phase 5B and 5C The soil profile analyzed was based on soil information from exploration location MW-9. An overburden stockpile was placed southeast of each mining cell. Flood irrigation, south of each mining cell, was simulated by raising the piezometric surface, at the fenceline (70-feet from the mining highwall), above the highest monitored surface to the ground surface. Longterm This stability run uses the lithology of Phase IA. The soil profile analyzed was based on soil information from exploration location ET02-131-105. Flood irrigation, north of WCR 64'/2, was simulated by raising the piezometric surface, under the road and in the borrow ditch just south of the existing road, above the highest monitored surface to the ground surface. The road is planned to be widened. The widening will result in the ditch being relocated southward. DRMS Analysis, Hgghwall Setback to Property Line The Division of Reclamation Mining and Safety (DRMS) requires that gravel pit highwalls within 200 feet of significant manmade permanent structures (such as utilities) be investigated for slope stability. Furthermore, the DRMS requires that the gravel mine highwalls be modeled as vertical unless it can be demonstrated that the slope angle of the highwall will be controlled during mining. Additionally, the DRMS requires that the analysis be performed using the DRMS parameters for sites where laboratory testing is absent. These parameters are given below on Table 2: Table 2: DRMS Model Parameters Soil Type Effective Friction Angle (degrees) Effective Cohesion c' (Psi) Saturated Unit Weight ., (Pct) Overburden 28 50 114 Gravel 35 0 130 Weathered Bedrock 14 0 124 Bedrock 28 100 124 The parameters for weathered bedrock are much more conservative than those typically encountered in the project area and, it is our opinion, that they are not representative of conditions at the site. We analyzed a vertical highwall section for each phase. The depth to bedrock varied from 7 to 31 feet across the project site. The vertical section corresponds to a steep highwall mining scenario where the highwall inclination is approximately 0.5:1. Table 3 below summarizes the results of our analysis. The analysis was performed using the DRMS parameters shown in Table 2. The factor of safety required by the DRMS for temporary mine slopes and reservoir embankments are provided for comparison. Output graphics for each of the analyses are attached. Parsons Mine DRMS 112 Permit Page SE5 of SE7