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 6 of 7 favorably oriented, which are conditions that control stability in jointed hard rock formations such as the basalt. Princeton Comment: Blasting Implication and Threats to Stability of the Slope Must be Addressed Before Approval Langan Response: There has been much discussion concerning blasting; however, Langan is not aware of any plan to blast rock at the site. Based on the available subsurface information, the homes closest to rock to be excavated are roughly 450-500 feet away. Langan maintains its opinion that if blasting is used to excavate rock, controlled techniques should be used to control impacts to the rock mass such as overbreak. Langan has no knowledge of the means and methods that will be selected by the Developer’s contractor to excavate soil and rock at Building D. However, the following paragraphs address methods of rock excavation that would be appropriate for the conditions encountered. As indicated in our 18 June report that the upper rock could not be penetrated by the excavation equipment used during the investigation which included John Deere 75G, CAT 308 and Hitachi 7X85 excavators, all of which are smaller than the type of equipment we expect to be used during construction. Nonetheless, specialized equipment is expected to be required for ripping rock. Hoek-Karzulovic, 2000; and, Abdullatif and Cruden, 1983 indicate rock masses having GSI values up to 40 (1 MPa) can be excavated by conventional means, rock masses having GSI values up to 60 (10 MPa) can be ripped, and for rock masses having GSI over 60 (>15 MPa) blasting has typically been utilized. Splitters and chemical expanders can generate pressures up to 43 MPa and 30-44 MPa, respectively. These methods work based on the tensile strength of rock, which is typically 6-15% of the rock’s compressive strength (Al-Bakri and Hefni, 2021). If the basalt at the subject slope has a GSI value of 20 as suggested by Princeton, we would expect the contractor to use conventional excavation methods, not blasting. Our findings indicate most of the section of rock mass to be excavated (i.e., the large outcrop roughly 450-500 feet from Howell Drive) has a GSI value of roughly 65 but is expected to range as low as about 50.

gs indicate most of the section of rock mass to be excavated (i.e., the large outcrop roughly 450-500 feet from Howell Drive) has a GSI value of roughly 65 but is expected to range as low as about 50. Such rock is expected to require some combination of mechanical methods to excavate, including large excavators or loaders equipped with ripping teeth or shanks, hoe rams, and splitters. However, locally and at a minimum as a starter method, splitters and chemical expanders would also be effective on the higher GSI material, as would controlled blasting methods. If controlled blasting is used to excavate the rock (including properly designed and implemented channel and line drilling), the blast should be designed to produce a locally (i.e., the building limits) fractured rock mass having the maximum quality such as a GSI value of 40-60 (i.e., least disturbance) that allows for mechanical removal. Regardless of the method used, the excavation should be designed by the contractor to prevent over breakage of the rock and damage to nearby structures.