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

MEMO Global Slope Stability Study for Building D West Essex Highlands Project Langan Project No.: 101049801 14 January 2025- Page 5 of 11 respectively. Boring LB-2 was terminated at about 50 ft below existing surface grade or at approximately el 472. Boring LB-4 was terminated at about 45 ft below existing surface grade or at approximately el 503. The top of rock contours are expected to vary considerably between investigation locations. Therefore, it should be noted that the top of rock elevations given herein are approximate and the reported conditions refer to the conditions at the specific investigation locations. Variations in the top of rock elevations, rock quality and weathering should be expected across the site. Laboratory Testing: Unconfined compressive tests were performed on 2 rock core samples taken from boring LB-3 located at the upper portion of the slope. The tests suggest that the unconfined compressive strength of the basalt rock samples varied between approximately 2,200 pounds per square inch (psi) and 3,500 psi or approximately 316,800 pounds per square foot (psf) and 504,000 psf. Groundwater The groundwater level could not be inferred from the moisture content of the soil samples during drilling. Water seepage at approximately 11 ft below existing surface grade in the decomposed rock layer was observed in test pit TP-1. Water seepage or indications of mottling were not observed in any other test pit. Surface water flowing over the sloping rock surface should be expected, especially during wet seasons. Groundwater levels are subjected to seasonal fluctuations. GLOBAL SLOPE STABILITY ANALYSIS As requested, Langan performed a global stability analysis of the subject area slope. The purpose of such a study is to evaluate if the slope is stable, with an adequate factor of safety, in the existing condition and in the proposed building loading condition. The analysis consisted of performing two-dimensional Limit Equilibrium Method (LEM) analyses for representative slope cross-sections to evaluate the global slope stability. During our study and analyses, we performed the following key tasks: 1. We reviewed the available geotechnical subsurface information along with our targeted subsurface investigation results for the subject slope area. 2. We reviewed the soil and rock geometry in the cross-sections along with the proposed building

urface information along with our targeted subsurface investigation results for the subject slope area. 2. We reviewed the soil and rock geometry in the cross-sections along with the proposed building gravity building loads. We chose two sections (section A and section B) across the proposed Building D footprint and down the subject area slope to the eastern residences for our slope stability analyses. Locations of Sections A and B are shown on Figure 1. 3. We estimated strength parameters for the soil based on visual observation and the collected N-value results obtained during sampling. = = =