When the sheetpiles as designed to 80’ encountered boulders and impassable obstructions at 30’ to 60’ deep and split apart at the joints to the surface the contractor was faced with the dilemma of shoring under water in order to dewater and excavate the conveyor trench to 60’ deep.

By installing 4” diameter permeation pipes to 80’ deep that had re-useable grout ejection ports at 2’ centers Southwest Contracting was able to place and control the cement/bentonite grout mix to “knit” the sand and gravels into a structural retaining wall 80’ deep where the sheetpiles stopped short. Later, the tremie seal was installed using the same method (shown above) between 60’ and 80’ so the excavation could proceed “in the dry”.