J_2024 05 09_West Orange Stormwater Management Plan

August 8, 2022 File No. 26.0092704.00 PSE&G – West Orange, NJ Page 11 Proactive by Design As previously indicated, when excavations for new foundations are performed adjacent to any existing foundations or other improvements to remain, if any, the new foundations should be located so that a line drawn between the lower edges of adjoining footings shall not have a slope steeper than 30 degrees with the horizontal, unless the material supporting the higher footing is braced or retained or otherwise laterally supported. Uplift loads may be resisted by the weight of the foundation, structure and soil within a prism defined by extending a line up and out from the edge of the foundation at an angle of 20 degrees from vertical. A total unit weight of 125 pounds per cubic foot could be assumed for the natural granular soils, excavated sandy fill, if any, or imported granular fill as previously specified to be used as backfill, provided the materials are compacted to at least 95 percent of their ASTM D-1557 maximum dry density. Horizontal loads may be resisted by friction between the concrete and soil, and passive pressure. An ultimate coefficient of friction of 0.35 for sliding may be assumed between the foundation concrete and the near surface silts and clays prevalent at the site. The coefficient of friction could be increased to 0.55 if crushed stone is provided below the foundations. Assuming the backfill is compacted as recommended, passive pressures may be calculated assuming a friction angle of 34 degrees (Kp = 3.5) and unit weight of 125 pounds per cubic foot. The designer should account for potential loss of support from freeze-thaw effects or future adjacent excavation if relying on passive pressures for shallow foundations. As such, we recommend that passive pressures be discounted for the upper two feet of soils due to potential disturbance. An Equal Opportunity Employer M/F/V/H