Impact of double shield tunnel construction on adjacent pile foundation in silty fine sand strata

Abstract

Abstract Shield tunnel construction inevitably penetrates pile foundations laterally in urban areas, resulting in surrounding ground movements and pile displacements. The engineering accidents occur when the deformation is out of limits, thus it is essential to grasp the pile deformation caused by shield tunnelling accurately. This paper presents a case study on the pile deformation caused by double shield tunnel construction in silty fine sand strata inNantong, China. The field monitoring program was con-ducted to observe pile settlement during the shield construction process. A practical method to estimate the induced pile settlement was proposed and verified. Moreover, a three-dimensional finite element model was established using Plaxis 3D software. The effects of grouting pressure, supporting pressure at excavation face, pile buried depth and other pile-tunnel geometry factors were examined. The re-sults indicated negligible differential settlements between piles and surrounding ground surface in the silty fine sand strata, which were significantly smaller than those in clay strata. The differential settlement of the piles on both sides of the tunnel reached its maximum as the shield tail of preceding tunnel passed through the pile. The supporting pressure of excavation face had most significant effect on the lateral deformation of the pile in the shield tunnelling direction. Moderate increase in the grouting pressure reduces the deformation and force of the pile effectively. The maximum settlement of the pile top was proportional to the diameter and buried depth of the tunnel, but was inversely proportional to the pile length and the horizontal distance between pile and tunnel. Furthermore, the risk status of the pile could be quickly identified by the risk level distribution map of piles, which facilitated the timely protective measures.