Design and Construction of Pile-Supported Mechanically-Stabilized-Earth Slope Stabilization-Paper

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After Hurricane Sandy, a coastal slope in Atlantic Highlands, New Jersey, experienced toe erosion, slumping, and movement of an existing timber wall. Finite-element stability analysis found the slope’s safety factor was below 1.2, less than the local code requirement of 1.5.<br /><br />A three-tier stabilization system was designed to fit the site’s steep terrain, narrow access, and limited budget. Its lowest tier used a grade beam, soldier piles, and concrete lagging, supported by deep piles extending into competent soils. The middle and upper tiers were constructed as geogrid-reinforced mechanically stabilized earth walls. Analysis using the strength-reduction method predicted a safety factor of about 1.8.<br /><br />Because conventional drilled-pile construction was slow and costly in the restricted work area, the team used precast concrete piles installed in pre-augered holes. Grout was injected through tubes cast into the piles to fill the annular space and improve pile-soil contact. Construction sequencing also allowed time for soils near the slope toe to consolidate, reducing pressure on the lower wall.<br /><br />The project was completed in about four months. Eight months of monitoring recorded less than 25 mm of lateral movement and less than 5 mm of settlement. The system therefore met its stabilization objectives while reducing costs from roughly $750,000 for a conventional retaining-wall alternative to slightly more than $200,000.

Keywords

Hurricane Sandy

slope stabilization

Atlantic Highlands

New Jersey

retaining wall

finite-element analysis

geogrid-reinforced walls

precast concrete piles

toe erosion

cost reduction