Secant piling is used to build concrete retaining walls often utilised for basement construction and flood defences. There are various different methods including hard/soft secant piling and hard/firm secant piling. Eco Foundations generally only install hard/hard secant walls as this method is the only truly waterproof system available. Others are only a compromise and will not achieve the level of waterproofing or get as close to the party wall as the hard/hard secant piling method can.

The continuous embedded retaining wall is constructed utilising alternate male and female piles. Female piles are drilled first using 35 or 40 newton concrete, reinforcing is installed and male piles are constructed the next day with the same concrete and steel overcutting the adjacent female piles.

The piles are drilled using a cased CFA double rotary piling system mounted on a telescopic leader rig. The casing ensures verticality and is designed to core through obstructions, concrete or old foundations. The design of the leader rig allows the wall to be installed within 25 mm of an existing building which when being used to construct a basement results in more square feet of usable space compared to retaining walls constructed with a conventional CFA piling rig which cannot work as close to the party wall.

The wall may well be left exposed in car park basements.