Case Study on the Design and Construction of ACIP Piles to Remediate a Slope Failure and Construct a Permanent Retaining Structure

This is a case study for a site near downtown Houston, Texas, where augured cast-in-place (ACIP) piles were used to remediate a slope failure and to construct a permanent retaining wall to reclaim land lost from the slope failure in an urban environment. A small scarp along the top edge of a 30 ft (9.1 m) deep ravine was first seen in 1977, and progressive failure resulted in a 17 ft (5.2 m) high scarp by 2006. The movement along the slope resulted in residual soil parameters in two clay layers that reduced the available shear strength for remedial repair. The failure scarp was very close to an access road, and future progressive slope failures that would damage the road could not be tolerated. The initial phase of construction was to build a temporary wall using ACIP piles between the failure scarp and the access road to stabilize the slope, and for construction of a work access ramp down into the ravine. The work area at the base of the slide was so confined and the clay subsoils were so soft that a small track-mounted ACIP rig was required to drill the piles for the permanent retaining wall. The ACIP piles were reinforced with steel "W" beams due to the high shear and bending stresses, and to act as shear keys to prevent a deep seated slope failure. The 20 ft (6.1 m) retaining wall structure has been in service for more than 15 years, and no problems have been reported. This case study will summarize the history, identify the critical problems, discuss the use of finite element analysis (FEA) for the design of the retaining wall, and discuss the construction of the retaining wall.