Project Description
The Student Housing Development included construction of a 13-story student dormitory building with retail space at the ground level, a six story student dormitory building, and a five-story parking deck. An approximately 15 feet high historic retaining wall constructed in 1926 by NJ Transit borders the southwestern corner of the site. This wall is being monitored for movement by NJ Transit, and plans to rehabilitate the wall are underway.
The subsurface conditions at the site consisted of historical fill followed by residual soil to depths of nine feet. Underlying the residual soils, weathered rock and competent rock were encountered. Oriented rock cores were obtained at the site to evaluate the strike and dip of the bedrock which was found to dip towards the historic retaining wall. Due to the dip of the rock joints toward the historic wall, slope stability analyses were conducted to evaluate the effect of the proposed loads on the slope (rock/soil). Rock slope stability analyses revealed that the rock would fail due to the stress imposed by shallow foundations, and thus cause the historic retaining wall to collapse. The presence of the historic retaining wall created a challenging engineering/economical solution and mandated use of both shallow foundations and drilled piers.
In order to investigate the subsurface conditions while maintaining the project schedule, Whitestone conducted the subsurface investigation in several phases. The Pre-Demolition Phase was preliminary in nature and included limited soil borings to provide preliminary geotechnical design parameters. The Post-Demolition phase consisted of drilling soil borings, rock coring, oriented rock coring, and detailed laboratory analyses to evaluate the rock durability and the feasibility of constructing an underground stormwater infiltration system. In addition, the Post-Demolition geotechnical investigation included rock joint mapping based on information gathered from oriented rock coring; slope stability analyses, and geotechnical value engineering analysis which resulted in two foundation systems (drilled piers and shallow foundation). Upon completion of the pier design, and in an effort to expedite the construction schedule, Whitestone recommended utilizing percussion drilling technology to evaluate the depth to the top of the rock and the rock quality in each drilled pier location. This allowed for pre-fabrication of the steel gage and reduction of individual pier rock socket length.
Prior to the start of construction, Whitestone conducted various environmental due diligence investigations in support of the proposed redevelopment project. Specifically, Whitestone performed a Phase I ESA, ACM survey, and Phase II Site Investigation (SI) prior to and following the demolition of the site buildings. Recognized Environmental Conditions (RECs) and contaminant conditions identified during the ESA and SI initially were addressed by the property owner’s environmental consultant. These RECs included a former sump pit, nine USTs, two contaminated soil hot spots, a below ground hydraulic lift, a hazardous material spill area and potential impacts to on-site groundwater conditions within the underlying bedrock. Due to the inability of the property owner’s site contractor to complete the work within the required time frames, Whitestone was retained to complete the remainder of the RI/RA activities including installing groundwater monitor wells, additional post-excavation soil sampling, contaminated soil disposal, and NJDEP reporting. Documentation from prior environmental due diligence investigations, remedial investigations, and remedial actions conducted by the site owner’s contractor and Whitestone were compiled into a comprehensive report for submittal to NJDEP with a request for No Further Action. Whitestone continues to provide environmental consulting services throughout the construction phase of the project in addition to acting as a liaison between NJDEP, the property owner, and financial institutions.