New Jersey Transit (NJT) Contract C13R involves excavation and support for the New York Penn Station Expansion (NYPSE) cavern along with its adjoining cross adits, access and utility tunnels, escalator tunnels and shafts, Cross Passages 1 and 2, the Dyer Avenue Cavern, and the Warrington Interlocking Caverns. Excavation is proposed to be by drill and blast methods followed by the installation of rock reinforcement and a reinforced shotcrete lining, generally described as rock support. The NYPSE cavern extends east-west for 495 meters from approximately below 8th street to 6th street. Two existing TBM tunnels traverse through the proposed location of the planned NYPSE station cavern separated by a central rock pillar.

The 30m x 30m cross section NYPSE station cavern is excavated in the Manhattan Mica Schist Group under approximately 13.5m of rock cover. The Manhattan Schist exhibits well-defined foliations along which the rock tends to split. The foliation and fracturing in this rock mass will lead to the rock mass behaving as a highly anisotropic medium. Past New York City tunnel construction case histories indicated that the high horizontal stresses may occur in the Schist and Granite groups, especially around plutons and other intrusions of granite into the Mica Schist. Consequently, a detailed assessment of the behaviour of the rock mass during tunnel excavation was required.

Dr Bedi was employed as a specialist sub-consultant to undertake geotechnical characterisation of the rock mass, followed by excavation assessment using advanced three-dimensional numerical analysis. Dr Bedi’s role involved an in-depth review of the geotechnical factual data in order to build an advanced constitutive model of the ground including the foliation and fracture characteristics and orientation, with respect to excavation, presence of groundwater, and the in-situ stress conditions. This constitutive model was then applied in a 3D numerical analysis to quantitatively assess the ground and tunnel behaviour of the NYPSE station. Due to the geometric configuration and complex excavation and support sequence the three-dimensional modelling incorporated explicit excavation and support sequence as well as shotcrete hardening.