2025 01 14 West Essex Highlands Development Building D Slope Stability Study

Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 14 January 2025- Page 8 of 11 MEMO Table 2B - LEM Factors of Safety against Sliding for Service Loads – Section B Condition Critical Slip Surface Critical Slip Surface That Reaches the Downslope Building Existing 1.67 6.46 Proposed 1.67 6.45 Seismic Slope Stability Analyses Seismic slope stability analyses have traditionally been performed by using pseudo-static limit equilibrium analyses. These analyses consist of applying a lateral force to the slope equal to the product of a seismic coefficient (kh) and the weight of the slope. The seismic coefficient is based on the actual anticipated level of acceleration in the failure mass and corresponds to some fraction of the anticipated peak acceleration (amax). Hynes-Griffin and Franklin (1984)1 seismic coefficient equation kh=0.5amax/g is considered appropriate to use for most slopes (Kramer, 1996)2. For this site, we utilized the Hynes-Griffin and Franklin (1984) criteria that resulted in kh=0.0875. To consider the effect of the proposed construction on slope stability, the critical slip surfaces for the existing and proposed seismic loading conditions for Sections A and B are provided in the tables below. LEM analysis results under seismic conditions are presented in Appendix E. Table 3A: LEM Factors of Safety against Sliding for Seismic Loads – Section A Condition Critical Slip Surface Critical Slip Surface That Reaches the Downslope Building Existing 1.65 2.23 Proposed 1.65 2.23 Table 3B: LEM Factors of Safety against Sliding for Seismic Loads – Section B 1 2 Condition Critical Slip Surface Critical Slip Surface That Reaches the Downslope Building Existing 1.29 4.59 Proposed 1.30 4.59 Hynes-Griffin Mary E; Franklin Arley G (2007). “Rationalizing the Seismic Coefficient Method”. Department of the Army. Steven L Kramer. “Geotechnical Earthquake Engineering” 1996. = = =