Secant piles are concrete cast-in-place drilled shafts installed so that they overlap to form a continuous wall. The installation sequence starts with drilling and pouring every other shaft: these are called the “primary shafts.” Once the concrete is set in the primary shafts, the drill returns to drill and pour the “secondary shafts.” An interlock is created between the primary and secondary shafts as the secondary shafts are drilled and poured, creating an impervious wall.
Secant pile walls make it possible to advance through man-made and natural obstructions (such as reinforced concrete, bed rock, cobbles, boulders, and dense soil), while avoiding any risk to settlement that could damage adjacent structures.
Secant pile walls and coffer dams can be poured with soft or hard concrete. They can be permanent and incorporated into the permanent structure as walls and foundations, e.g. the foundations, shear walls and underground parking of large buildings.