Techniques & Systems

Secant Bored Pile Retaining Walls

This system involves constructing interlocking bored piles to form a continuous concrete piled wall suitable for water bearing ground conditions. The un-reinforced primary piles are constructed first, often using Continuous Flight Auger techniques. These piles are drilled on a hit and miss basis to avoid damage to recently cast piles.

The secondary piles are then drilled using cfa or heavy duty rotary rigs to cut into the adjacent Primary piles. The depth of the cut is typically 150mm but will be designed to take into account the depth of the excavation and the verticality tolerances that can be achieved.

Various grades of water tightness can be obtained by the use of a secant piled wall together with an engineered lining or cavity wall.

Where obstructions are anticipated, for example from foundations associated with previous developments, it is possible for the heavy duty rotary piling rigs with segmental casing to penetrate brickwork and lightly reinforced concrete. This will provide an engineered solution to maximise the floor area of the new development up to site boundaries. The need to remove existing perimeter foundations by excavation can be avoided.

Scheme designs can be developed to minimise the requirement for temporary propping by either designing the wall to cantilever as much as possible or by providing for a top-down construction technique.

Reinforcement cages can be designed to suit the retained heights and any propping forces acting on the wall. Special reinforcement can be incorporated into the pile cages to allow connection to be made to floor slabs/beams.