Comparisons of Two Approaches for the Design of Retaining Walls Supported on Drilled Piles

Retaining walls supporting lateral earth pressure over more than 6 meter depth may require a wide foundation to satisfy all stability requirements. In urban areas excavation width can be of concern when heavy traffic and nearby existing structures can be seriously affected during project construction period. The design choice of placing the retaining wall on a narrow beam supported by piles is well suited to urban areas where space constraints and damage to adjacent structures are major considerations. This work investigated design approaches using two methods in order to arrive at an optimum geometric design. The first approach treated the retaining wall and beam system as a separate unit and piles as another unit supporting lateral load and moment at the top in addition to axial and frictional loads. The second approach considered monolithic system in which both the piles and retaining walls are treated as a one unit. SAP 2000 program was used to compute all moments and shear forces based on the same input data implemented in the first approach. The outputs of the two approaches are compared and discussed and validation of the final design output is reviewed. Recommendations on selecting geotechnical design parameters for the two approaches are presented.