How to Use Secant Piles


Secant piles are drilled shafts filled with concrete used as a wall below the ground. A secant is a mathematical term describing a line that intersects a curve or circle at two points. Secant pile walls are constructed with the shafts of concrete overlapping, or intersecting, one another. Applications for secant piles include transferring foundation load through layers of weak soil until they reach a load-bearing soil, for earth retention and as a water control barrier.

Things You'll Need

  • Pre-installed guide wall
  • Vibro-hammer
  • Auger
  • Crane
  • Casings
  • Steel-reinforced cages
  • Slow-setting concrete
  • Bentonite slurry
  • Install a casing through every other opening (1, 3, 5, 7, etc.) in the guide wall. Use the vibro-hammer to push the casing down into the earth. Approximately 1 meter of the casing should remain above ground.

  • Remove the soil from inside the casings with the auger. This will create the primary boreholes. Bentonite slurry can be used as a support to the ground below the casing if the casing is not long enough to reach the designed depth.

  • Pour slow-setting concrete into the first two primary boreholes until it reaches ground level. Before the concrete is set, use the auger to drill and remove the soil from between the primary casings. Remove the casings from the two primary piles (columns) using the vibro-hammer.

  • Install a casing into opening 2. The toothed edge of the casing will cut into the still-unset concrete of the primary piles, overlapping them on both sides by 3 inches (8 cm).

  • Lower the steel-reinforced cage into the casing of opening two using the crane. Pour concrete into the secondary borehole.

  • Continue building the secant wall by repeating the following steps. Use the auger to remove the soil from the next primary borehole. Pour concrete into the borehole until it reaches ground level. Use the auger to remove the soil from the next secondary borehole. Remove the casing from the primary borehole. Install a casing in the secondary borehole. Lower the steel-reinforced cage into the secondary casing and fill the casing with concrete.

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