Langan Rebuttal Report 9 15 2025

Global Stability Study for Eastern Slope near Building D West Essex – Highlands Development West Orange, New Jersey Langan Project No.: 101049801 15 September 2025 Page 4 of 7 relatively lower unconfined compressive strengths to “significant weathering”, which failed to recognize that other properties such as porosity and microstructural attributes (grain size and shape) tend to govern the unconfined compressive strength of brittle rock (Gueguen & Bouteca, 2004). Princeton’s 12 August model of sections C and D utilized a GSI of 20 and a UCS of about 2300 psi. Rock material having the Princeton assigned values would equate to a very poor quality seamy/disturbed rock or a poor quality disintegrated rock. However, our summary of the rock structure and quality in the table below shows a narrow range in structure from predominantly blocky to very blocky (at one location) and generally good quality to fair quality rock. The upper 5 feet of the rock at NLB-1 (our analysis section C-C and Princeton’s model section C) exhibits rough slightly weathered joint conditions, which are considered Good surface quality within the GSI system, not very poor surface quality as suggested by Princeton. In addition, field estimates of typical intact rock strength are shown to range from roughly 3,625 psi to 36,250 psi, the upper end of which is more closely associated with basalt. Nonetheless, we modeled analysis section C-C using a GSI value of 37 and a comparatively low intact rock strength and there was no change in the factor of safety (Exhibit B). Rock core photos are provided in Exhibit C. Princeton’s reference to using a factor of safety of 2.0 is simply not applicable. The EM 1110-1-2908 reference is applicable to US Corp of Engineer facilities built on rock that experience a lateral load (e.g., a dam), which if the slope failed would be catastrophic to neighboring properties. This development clearly does not apply. A factor of safety of 1.5 is applicable for the subject slope. Rock deformation modulus, which is measure of a rock mass’s resistance to deformation under load, calculated using a GSI of 20 and Disturbance factor of 1 (Hoek and Brown, 2018), indicates a range in values of 35 to 68 MPa, which is only 2 to 4 times greater than the unconfined compressive strength of the rock. The modulus should be hundreds of times greater than the unconfined compressive

ange in values of 35 to 68 MPa, which is only 2 to 4 times greater than the unconfined compressive strength of the rock. The modulus should be hundreds of times greater than the unconfined compressive strength of the rock. Therefore, using a GSI of 20 is not representative of the rock mass throughout the site. For comparison, the estimated deformation modulus of rock having a GSI of 65 ranges from about 2,000 to 8,000 MPa depending on the Disturbance factor.