Theoretical prediction of the potential plastic zone of shallow tunneling in vicinity of pile foundation in soils

摘要

It is often unavoidable for metro tunnel constructions to disturb and be affected by nearby existing structure foundations. In order to predict and control the interactions between the tunnel construction and the mechanical behavior of the existent structures, it is necessary to evaluate the degree and extent of tunneling disturbance to the ground, especially the shape and range of the potential plastic zone in tunneling-induced secondary stress field. In this regard, existing theoretical solutions are in general all based upon the premise that the ground is free from structure foundation loads. The present study, assuming homogeneous and isotropic ideal elasto-plastic soil, presents a theoretical procedure for prediction of the secondary stress field and the related potential plastic zone caused by tunneling in the vicinity of pile foundations. The procedure involves superimposing the analytical solution for tunneling in greenfield with the analytical solution for pile foundation loads. Calculations are conducted as examples to compare the theoretical results with corresponding numerical simulations and to demonstrate the effects of the position, magnitude and pattern of pile foundation loads on tunneling induced plastic zones. The calculations reveal that the proposed theoretical calculation procedure produces similar results as from numerical simulations, and that pile foundation loads of sufficient magnitude, if close enough to the tunnel, may significantly alter the potential plastic zones caused by nearby tunneling.