Secant Piles Construction Explained
Underground Metro Station constructed using Secant Piles
A secant pile wall is constructed using intersecting cast in-situ bored piles. Soft Piles do not have reinforcement, are constructed firstly alternatingly. Hard piles that have reinforcement are constructed between and are cut into the soft piles.
The secant pile wall forms an underground retaining wall that will support the faces of excavation and hold back the ground water.
The Construction sequence for the Secant Piles is:-
A concrete guide beam is constructed with curved faces, used to locate the pile drilling positions.
The soft piles are bored, bentonite a mixture of water and a special clay is used to support the excavated hole from collapsing and concrete is poured into the bored hole.
The hard piles are constructed as the soft piles with a prefabricated reinforcement cage inserted prior to concreting.
The Excavation & Propping Sequence for the Secant Piles is:-
The reinforcement at the top of the hard piles is exposed and a concrete ground beam is constructed that connects the hard piles.
Excavate to below the steel bracing level
Install Walers and Struts. Alternatively walers and ground anchors could be used.
Excavate to formation
Construct reinforced concrete floors and walls.
Shown is how a reinforced concrete wall is constructed. The activities are reinforcement fixing, erect shutters, pour and vibrate concrete and remove shutters after the concrete has hardened.
Shown is a piling operation and the plant and equipment used