Drill and grout seal. Drilled and installed grout valves to 80' deep in gravel, cobble deposit. After hydraulic testing, controlled pumping of 17,000 bags of grout formed an impermeable wall and tremie seal.
When the sheetpiles as designed to 80’ encountered boulders and impassable obstructions at 30’ to 60’ depths 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’ depth 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”.