Design, Construction, and Performance of an Anchored Tangent Pile Wall for Excavation Support

Excavation for a building in Washington, D.C. required support systems to limit the deformation of several adjacent structures. One adjacent structure would have been difficult to underpin conventionally because column footings are located approximately 13 feet behind the face of the excavation. A geo-support system consisting of tangent piles and two rows of tieback anchors was presented as an alternative to direct underpinning. In order to predict potential ground movements adjacent to the 27-foot deep excavation, tangent piles were analyzed as beam-columns subjected to lateral earth pressures, footing surcharge loads, and anchor loads. Deformations of the adjacent building were monitored during construction for comparison with the predictions. In addition, the drilled shafts of the tangent pile wall were used as a permanent foundation for the new building columns. This paper describes the design, analysis, construction and performance of the anchored tangent pile wall. This case history demonstrates the effectiveness of using this configuration of drilled shafts to limit ground movements in deep excavations close to existing structures.