Abstract: The effect of further downward excavation beneath an existing building on the pile foundation is different from the one encountered in a newly-created excavation case. Based on the finite-element parameters derived from a case history, a hardening-soil model and a contact-surface model are adopted to simulate the characteristics of soil and the pile-soil interaction, respectively. The three-dimensional finite element framework takes into account the interaction of piled raft foundation, ground and excavation, and is able to investigate the vertical bearing behavior of the existing pile groups after the excavation. The investigation accounts for the effects of end-bearing soil stiffness and excavation depth on the variation trends of pile-head rigidity, pile force, pile shaft resistance, ratio of pile base resistance and soil rebound. The results show that individual piles in an existing pile group subjected to further excavation behaved differently. Increasing the stiffness of the end-bearing soil is crucial to enhancing pile capacity and the critical ratio of pile base resistance. The excavation depth is a key factor that positively influences the mobilization degree of the shaft and base resistances of existing piles. The present results are possible to assist the deformation control of structure underpinning and the design of supplemented pile for further excavation under existing basement.

Key words: existing building, excavation, group-pile foundation, three-dimensional finite element method