Unconventional Drilled Pier Underpinning

An “unconventional” earth retaining system consisting of drilled underpinning piers, was used successfully to underpin a four- story building in Redwood City, California. Considerations to other conventional underpinning systems and their feasibility at the subject site are also examined. An in-depth discussion of the unconventional underpinning system selected for the project is presented with details of the construction sequence and difficulties encountered. Post-construction performance of the underpinning system and the relative costs of the “unconventional” underpinning system are also presented