Abstract: With the stereo development and utilization of underground space, problems related to structure interaction are increasingly important in underground approaching construction projects. This paper proposed an analytical method based on cavity expansion (contraction) theory in geomaterials to solve the problem of tunnel excavation under-crossing a displacement pile. By adopting the unified clay and sand model and the large-strain assumptions, a mechanical model for tunnel-pile interaction was established in regards to the two dimensional problem. With the influence of tunneling volume loss, a reduction factor of pile bearing capacity was proposed, and the load-settlement response was then employed to predict tunneling-induced pile settlement. The analyses indicated that tunnel volume loss induced the reductions of both pile shaft and pile end bearing capacities, as well as the stiffness of surrounding soil, which all led to pile failure. Additionally, relationships to link tunnel volume loss to tunnel-pile distance, bearing capacity reduction factor, initial safety factor, and soil initial state parameters were obtained at pile failure, which ultimately contributes to understanding of the mechanisms of tunnel-structure interaction and the stability of underground structure.

Key words: tunneling, displacement pile, cavity expansion theory, elastic-plastic model, large strain