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 9 of 11 MEMO Parametric Sensitivity Analysis due to Groundwater Level We performed sensitivity analyses to evaluate the impact of groundwater on the slope stability for the static loading condition. We evaluated the groundwater effect with the groundwater level located immediately below the topsoil layer, at the top of the decomposed rock/very dense sand layer and at the top of the rock stratum. The estimated resulting factors of safety are provided in Table 4A. Table 4A: LEM Factors of Safety against Sliding for Gravity Loads with Groundwater Groundwater Level Section A (Critical Slip Surface) Section B (Critical Slip Surface) Immediately Below Topsoil 1.36 1.54 Top of Decomposed Rock / Very Dense Granular Soil 2.20 1.67 Top of Rock 2.26 1.68 We also performed an infinite slope analysis for the varying groundwater level conditions as part of the sensitivity analysis. The critical slip surfaces were modeled to be at varying groundwater levels. The estimated resulting factors of safety from this analysis are provided in Table 4B. Table 4B: LEM Factors of Safety against Sliding for Gravity Loads with Groundwater (Infinite Slope Analysis) Groundwater Level/Critical Slip Surface Location Section A Section B Immediately Below Topsoil 3.44 3.09 Top of Decomposed Rock / Very Dense Granular Soil 3.94 3.87 Top of Rock 5.28 4.57 EVALUATION We utilized the NAVFAC Design Manual 7.1 “Soil Mechanics” (NAVFAC 1986) reference in the evaluation of the factors of safety calculated in our global slope stability evaluation for the static and seismic design loading conditions. This manual indicates that a factor of safety of no less than 1.5 should be utilized for permanent or sustained (static) loading conditions of slopes. This manual indicates that a factor of safety of no less than 1.15 should be utilized for seismic loading conditions of slopes due to earthquakes. = = =