Secant Wall

SECANT PILE WALL DESIGN FOR DEEP EXCAVATIONS

Secant pile walls are formed by constructing intersecting reinforced concrete piles. The secant piles are reinforced with either steel rebar or with steel beams and are constructed by either drilling under mud or augering. Primary piles are installed first with secondary piles constructed in between primary piles once the latter gain sufficient strength. Pile overlap is typically in the order of 3 inches (8 cm). In a tangent pile wall, there is no pile overlap as the piles are constructed flush to each other.

The main advantages of secant PILE WALLS are:

• Increased construction alignment flexibility.
• Increased wall stiffness compared to sheet piles.
• Can be installed in difficult ground (cobbles/boulders).
• Less noisy construction.

The main disadvantages of secant pile walls are:
1. Verticality tolerances may be hard to achieve for deep piles.
2. Total waterproofing is very difficult to obtain in joints.
3. Increased cost compared to sheet pile walls.

Secant pile wall design when steel beams are used involves the use of weaker than normal concrete. The pile that is lagging the wall between two main beams has to be examined for shear and compression arching.