A secant pile wall is an interlocking system of bored/CFA piles used to create a continuous, watertight shoring or retaining structure. Unlike soldier pile walls, which leave gaps between individual piles, secant walls overlap, with each pile taking a deliberate “bite” into its neighbours to eliminate voids and resist water ingress.
The result is a robust, water-resistant wall that can retain earth and manage groundwater in basements, excavations, and temporary retaining structures, particularly in coastal, sandy, or high-water-table environments where conventional shoring is insufficient.
Secant walls can be constructed using either bored or CFA methods; APG carries both and has the ability in using casings for both applications; and selects the right method based on ground conditions and project requirements.
In loose, water-charged soils, the hard part is keeping every pile within tolerance, so the interlock holds at depth, and you only know you have it once the basement is exposed. APG has delivered that on projects of five to eight basement levels, including a 500-pile secant wall on the Parramatta River to South Australian water infrastructure.
Cronulla, Coogee, Penrith, Parramatta, Adelaide. Our secant wall experience spans coastal sands, riverbed clay, and urban high-water-table environments across multiple states underlaid by strong rock.
Because we specialise in bored, CFA, cased, and secant piling, we can assess whether a secant wall is genuinely the right solution and design the methodology around your specific ground conditions, rather than a standard template.
Where high water tables or permeable ground make standard shoring inadequate, secant walls provide a watertight retention solution that manages water ingress to a controllable level.
Sandy coastal ground allows water to travel rapidly, making secant pile walls the go-to shoring solution for basement construction in Sydney’s eastern suburbs, northern beaches, and coastal regions.
When a project needs to retain a higher level to a lower level during construction, and ground conditions make other retaining solutions impractical, secant walls provide a reliable temporary structure.
A guide wall is installed first to maintain pile alignment and verticality across the full wall length.
Alternate piles, known as soft piles, are drilled and filled with low strength concrete, no reinforcement. These set the interlocking reference points for the wall.
Once soft piles have set, hard piles are drilled between each pair, taking a bite into the adjacent soft piles on both sides. These carry the reinforcement cage and do the structural tension work.
The result is a continuous interlocking wall with no gaps, significantly reducing water flow compared to soldier or contiguous pile walls, and providing a structurally sound retention system.
