At the Spring Street Parking Garage in Princeton, N.J., severe artesian conditions caused cracking in the concrete slab of the basement level. Structural Preservation Systems (SPS) was called upon to install permanent rock anchors to hold down the slab and prevent further cracking. The main obstacles were low headroom conditions and the hydrostatic water pressure encountered when penetrating through the slab to the overburden above the rock. SPS implemented complex, innovative techniques using a low headroom electric drill rig to install the anchors. Three strand cable anchors were used to achieve 50-kip loads and four strand anchors were used to achieve 75 and 100-kip loads. All anchors were double corrosion protected.

A core drill was used to core a 6-inch hole through the slab, followed by the electric drill rig that used duplex drilling methods to drill the holes through overburden and rock to approximately 50 feet in depth. Geotextile socks were used to overcome challenges with grouting in the hydrostatic conditions.