Construction of a deep shaft for repair of the Coxwell Trunk Sewer encountered ultra-fine quicksand soil conditions at the interface between the original tunnel lining and shaft excavation that could not be dewatered using conventional well points.
Shaft wall construction consisted of secant piles down to the top of existing sewer tunnel, with subsequent jet grouting to close residual areas surrounding and beneath the existing sewer tunnel. Due to complex geometry at the shaft lining to tunnel lining interface, residual layers of ultra-fine soils remained under high hydrostatic water pressure that flowed into the shaft excavation and delayed construction work.
Based upon past experience with other similar projects, Peter White developed a drilling and grouting plan involving sodium silicate injection, in conjunction with the use of water-activated polyurethane resin, to systematically consolidate and stabilize water-bearing, ultra-fine soils so that shaft excavation could proceed in a safe and controlled manner.
Shaft excavation crews, with assistance from Peter White’s technical personnel, were able to successfully stabilize quicksand conditions and proceed with the remaining excavation work required to complete construction of the Coxwell Trunk Sewer Bypass.