A mining contractor was constructing a surface collar for a new ventilation shaft and encountered quicksand conditions at the interface between the sheet pile perimeter wall and underlying rock strata that delayed the deep shaft excavation. Rock strata were too hard for sheet pile tips to penetrate, resulting is openings beneath adjacent sheet piles. Excessive excavation had destabilized the surrounding soil mass and caused sinkholes to occur adjacent to the shaft collar.
Working from within the shaft, grouting engineer Peter White and his technical crew commenced chemical grouting operations at the highest point along the rock-sheet pile interface using water-activated polyurethane resin and systematically stabilized soil conditions around the perimeter of the shaft to prevent soil or water from infiltrating.
The shaft sinking contractor was then able to install steel plates to reinforce the grouted openings prior to continuing with the excavation work. The grouting crew continued working to systematically eliminate problems at lower elevations with quicksand inflows until the entire perimeter was sealed.
The final stage of grouting work was to stabilize a ring of soil outside the shaft at the soil-rock interface so that the shaft collar would withstand subsequent rock blasting within the shaft.
After 10 days of chemical grouting work that consumed over 1,500 kg of chemical grout, all the shaft bottom had been excavated down to solid rock with no further water infiltration.
“Shaft Collar Construction Through Quicksand Ground Conditions” – by Peter White, P.Eng.