COMPLIANCE INFO_FINAL WMU FU-23 DESIGN RPT & CONCURRENCE LTRS

Home Browse Search

WMU FINAL WMU FU-23 DESIGN REPORT 2-18-23 3-1 SECTION 3 Slope Stability In accordance with Title 27 regulations, static and seismic stability analyses were performed for WMU FU-23. Refuse placed on the southern side of WMU FU-23 will be consistent with the final landfill grades. The northern and eastern slopes of WMU FU-23 are temporary slopes and will be filled against once adjacent cells to the east and north are constructed. The western refuse fill slope overlies WMUs FU-17 and 19. Based on the geometry, construction against adjacent WMUs, and site development plans, the planned maximum refuse fill elevation in WMU FU-23 is approximately 110- feet. Critical stability configurations were assessed based on the Construction Drawings and WMU FU-23 refuse grading plan. The section analyzed is an east-west cross section through the eastern slope at the maximum interim fill elevation of 110-ft MSL. 3.1 Analytical Method STATIC ANALYSIS The slope stability analyses were performed using the computer program XSTABL. The program calculates slope stability using a limit equilibrium analysis based on the method of slices. The method of slices estimates slope stability by assuming a shear surface and calculating the forces that would cause slope movement, and the forces resisting slope movement for the selected shear surface. The ratio of available shear strength (resisting forces) to mobilized shear strength (driving forces) is known as the factor of safety. The computer programs employ a searching routine to determine the critical shear surface with the minimum factor of safety. A factor of safety equal to 1.0 under static loading conditions represents a condition of imminent failure. For temporary slopes, a minimum factor of safety of 1.3 under static loading conditions is considered acceptable. Permanent slopes are typically designed to achieve a minimum static factor of safety of 1.5. SEISMIC ANALYSIS During a seismic event, the propagation of bedrock motions induces a sequence of cyclic shear stresses on the soil and refuse. These cyclic shear stresses result in cyclic strains. When the stresses are above yield, a certain amount of strain remains, which produces permanent seismic deformations in the soil or refuse. To estimate these seismic deformations, the Bray and Rathje, et al. (1998) procedure was used. When evaluating the results of a seismic deformation analysis, the effect of the net slope movement should be considered. The most severe consequence of slope movement would be damage to the composite base lining or LCRS of the landfill. While it is difficult to assess what deformation would damage a composite base lining system, the current practice is to limit deformations to 30 cm (1 foot) or less (Sharma and Lewis, 1994).