Performance Of Anchored Pile Walls For A Deep Cut

The Banora Point Upgrade Project in NSW Australia comprised key features including two interchanges, a 300m long viaduct, a large cutting through Sexton Hill with an associated 100m wide Land Bridge and retaining walls reaching 490m in length and up to 22m high. The geology at Sexton Hill comprises a volcanic succession of variably weathered basalt flows and agglomerate deposits overlying Mesozoic sedimentary rocks at a depth of approximately 48m beneath the crest of the hill. Two types of retention system were selected to support the Sexton Hill cutting and were required to suit the ground conditions, satisfy the performance criteria and consider the narrow project corridor. These included cantilever/anchored piled retaining walls and soil nail walls. The paper focuses on the design approach and numerical modelling techniques and compares the predicted and actual performance of the anchored pile wall system based on the monitoring data collected during and post construction. Numerical analyses using computer programs PLAXIS, Phase² and WALLAP have been undertaken to model the behaviour of the anchored pile wall including wall deflections and anchor loads. In addition, the analyses sought to determine whether neighbouring residential properties were adversely affected by the construction of the cutting. The predicted values of anchor loads and wall deflections have been compared with actual performance and are presented. A back analysis has been performed focusing on a portion of the retaining wall section where the predicted and actual performance differed significantly. The results from the back analysis revealed that the deflections displayed by the piles are particularly sensitive to small changes in stiffness of high strength rock just above the final excavation level.