What Is Secant vs. Tangent Pile Wall?
Secant and tangent pile walls are both drilled-shaft excavation support — the difference is the overlap: secant piles interlock (the secondary cutting the primary — the watertight wall), tangent piles touch (the piles adjacent — the soil's arching between, the water passing). The selection: the groundwater (the secant's cutoff vs. the tangent's drainage), the cost (the tangent's economy), and the retention (both cantilevered or braced).
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Secant: the watertight
The overlapping (the 3-6 inch interlock — the continuous concrete; the groundwater cutoff), the sequence (the primary then the secondary — the timing), and the applications (the below-water excavations — the basements, the shafts; the contaminated — the containment). The cost (the overlap's drilling — the premium).
Tangent: the economical
The touching (the piles adjacent — the soil arching; the water's passage — the dewatering designed), the simplicity (the single-pass drilling — the speed), and the applications (the above-water cuts — the hillside; the temporary — the construction support). The limitations (the caving soils — the arching's failure; the water — the inflows).
Selection and design
The groundwater (the deciding — the cutoff needed or not), the retention (both designed for the earth pressures — the structural similar; the secant's water adding the hydrostatic), the construction (the secant's precision — the verticality; the tangent's tolerance), and the cost (the tangent's 20-40% savings where the water allows). The engineer selects by the water — the wall follows the groundwater.
The bottom line
Secant piles overlap forming the watertight cutoff (below-water excavations); tangent piles touch relying on soil arching (above-water, 20-40% cheaper). Select by groundwater.
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