Secant Piled Walls
Secant piled walls are typically used to control and reduce the ingress of groundwater. Often used in basement construction, but can be used in various other scenarios where vertical retaining structures are required be it earth, water or both. The secant wall will normally but not always form a part of the permanent works. As you can see below a secant wall is made up of interlocking bored piles. The hard piles (males) are reinforced with the soft piles (females) form the joint and have no reinforcement.
Contiguous Piled Wall
These are similar to piled secant walls with the exclusion of the female piles. Contiguous walls are normally suitable in dry soils where only earth or other materials require retention. A contiguous piled wall can be used for all the same applications as a secant piled wall but normally where ground water control is not required.