Numerical Study on the Effect of Large Deep Foundation Excavation on Underlying Complex Intersecting Tunnels

Abstract

The effect of large deep foundation excavations on the surrounding existing tunnels is a problem that cannot be avoided in the current construction background. This effect is difficult to assess precisely, especially when the geometry of the tunnels and pits is complex. In this paper, a three-dimensional (3D) finite element model has been developed based on a case containing four complex intersecting tunnels and a large deep foundation pit. The model used the hardening soil model with small-strain stiffness (HSS) and the Hoek–Brown (HB) model to describe the mechanical properties of the soil and rock, and various methods including the standard penetration test (SPT) and heavy dynamic penetration test (HDPT) were used to determine the model parameters. The results of the analysis are as follows: the excavation of the foundation pit caused the tunnels to heave and the heave deformation conforms to the normal distribution; the maximum heave of numerical simulation is 3.1 mm which is consistent with the field data; the horizontal displacement, horizontal convergence, and vertical convergence of the tunnels caused by the excavation of the pits are small, and all kinds of deformations meet the control requirements; the intersection of multiple tunnels shows obvious stress concentration when the tunnels were constructed, and the lining stress slightly decreases as excavation progresses.