Large-Scale 1-g Model Tests on the Interaction Between Excavation Support Structure and Nearby Multi-Type Cushioned Piled Rafts: A Comparative Study

Undertaking new foundation pit excavation in a congested urban dwelling is characterized by the associated unfavourable outcomes in the surrounding area and hence continues to evolve a performance problem involving intricate soil-structure interactions. Despite decades of effort to analyse the response of conventional pile foundations to nearby excavations, performed experiments were limited to either single and group piles or elevated connected piled rafts. This paper intends to collate and examine the in-house 1-g experimental results from the past few years on the performance of supported excavations in close proximity to composite piled rafts, as well as the excavation-induced changes in the load-carrying capacity of foundations with multi-type piles. First, the additional earth pressure on the retaining wall is introduced under the mode of wall translation and/or rotation about the base, taking into account the stress redistribution and shielding effect of the piles, which leads to a reduction of the lateral pressure as compared to estimations from the traditional procedures. Second, the influence of wall movement progression on the load-bearing capacity of the foundations with varying pile lengths/stiffness is compared, demonstrating the reduction of the load borne by the soil beneath the cushion to proportionally transfer onto the piles. Experimental results from centrifuge tests are then compiled to shed light on the influence of excavation execution sequence. Furthermore, parametric numerical analysis findings on the load-sharing and lateral response of the piles are included. The article would assist researchers and practicing engineers to comprehend the mutual interaction between composite pile foundations and new excavations.