What is the difference between tangent piles and secant piles?

Secant piles walls use overlapping shafts that are very stiff and provide an effective barrier in groundwater. Tangent piles are similar to secant piles except the shafts do not overlap.

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Secant Pile Wall Construction and Installation

Secant pile walls are constructed by drilling in a series of alternating primary (drilled first) and secondary (drilled second) overlapping shafts to form a continuous wall. The concrete in the shafts can be all low-strength, all high-strength, or a combination of low-strength primary and high-strength secondary shafts. Steel piles or reinforcing steel is typically placed in the secondary shafts. Unreinforced high- strength shafts can also be constructed in a self-supporting circular ring, such as those frequently used for access shafts to tunnels.

Secant pile walls are relatively impermeable and can be used to control the flow of groundwater into an excavation and limit draw down outside the excavation. Secant pile walls are also very stiff and are often used when there are sensitive structures behind the wall.

An advantage of using secant piles for cutoff wall construction is the ability of Schnabel’s high torque drill rigs to penetrate hard drilling conditions while simultaneously casing the drill hole. These drills can advance a cased hole through man-made and natural obstructions including cobbles, boulders, and reinforced concrete.

When difficult drilling conditions are anticipated, secant piles can be a very economical method for cutoff wall construction. Another benefit is the relatively low cost of mobilization when compared to other cutoff wall types such as slurry walls and soil mix walls. To learn more about whether a secant pile wall solution is right for your project, contact one of Schnabel’s eight regional offices today.

Always innovating new approaches to better solve old problems.

Rondout West Branch Bypass Tunnel Shaft

Schnabel installed secant piles in a self-supporting circular ring configuration to support the construction of a new bypass tunnel under the Hudson River in New York City after an older tunnel started to leak.

Barnes-Jewish Hospital

Schnabel designed and constructed a secant pile wall for the Barnes-Jewish Hospital Parkview Tower on the Washington University Medical Campus in St. Louis, Missouri. The perimeter secant pile wall served as both the permanent structural basement wall and the temporary earth retention system for the new hospital building.

In 31 years of building deep foundation projects for Schnabel, building a 90’ deep reinforced circular shaft was one that was very challenging and deeply rewarding. Looking forward to working on the next one with our client Schiavone.

Paul Davis, Rondout West Branch Bypass Tunnel Shaft

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Schnabel is the sector’s most operationally efficient Geostuctural Design & Construction contractor. We optimize efficiencies by leveraging decades of experience and design/build expertise, to innovate processes and approaches that are consistently proven to deliver optimal outcomes for our clients.

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