Secant piled shafts are the preferred method of constructing watertight shafts in depths of up to 25 metres. The shaft wall is formed by drilling holes of approximately 1.0 metre in diameter and filling them with concrete. The caissons are drilled overlapped to provide watertightness and structural integrity. A steel pile may be inserted in the concrete caisson to provide additional shaft strength.
Technicore is atypical in the tunnel industry in that it maintains its own drilling equipment and constructs its own secant-piled shafts and excavation supports.