Drilled concrete pile walls, also known as secant walls, are created when the individual drilled caisson holes intersect and are called secant or caisson walls. These walls are more expensive than most shoring solutions but offer minimal movement.
These walls are constructed by drilling overlapping caisson holes. Primary piles are first drilled at a specific spacing and filled with concrete. Secondary or Soldier Piles are drilled in between the primary piles such that they overlap by a set amount, drilling out part of the concrete from the primary piles on each side. The soldier piles typically have an h-beam or rebar cage placed inside to provide reinforcement. After the hole is drilled and reinforcing placed, concrete is then poured as the casing is raised, creating a strong interlocking wall of circular caissons. As can be seen in the picture below, once excavated the curved face is often chipped off to make a flat surface inside the excavation.
These walls are usually paired with tie-backs drilled through the wall to provide stability and sometimes have whalers along the exposed face.
Bermingham has extensive experience building these walls, typically utilising 880 mm to 1500 mm diameter tooling and as deep as 42 metres (136 ft). In one recent condominium project Bermingham used this technique for the first eight-storey underground parking garage in downtown Toronto.
Bermingham utilises its fleet of Euro-style drill rigs for this work.