Influence of foundation piles on narrow excavations stability in soft soil areas

Narrow excavation is a common type of excavation which is widely used in urban comprehensive pipe corridor projects, while little research exists. In this paper, the finite difference software Flac3D is used to study the influence of foundation piles in the excavation on the stability of narrow excavations, taking a typical section of Nansha comprehensive pipe corridor excavation in Guangzhou as the prototype. The results show that the existence of foundation piles in the excavation will increase the stability of the excavation to a certain extent, and the foundation piles in the excavation will be subjected to bending failure when the excavation is unstable. The analysis without considering the plastic bending failure of the foundation piles will overestimate the stability of the excavation to a certain extent. As the width of excavation decreases, the safety factor of excavation increases, but the effect of foundation piles decreases. Foundation piles are placed close to the retaining structures and the increase of pile diameter will improve the stability of excavation. The effect of pile length on the safety factor of excavation depends on the strength of embedded soil, and when embedded in hard soil, the safety factor of excavation will be greatly improved. A new simplified calculation method is proposed to evaluate the basal heave stability of excavation with foundation pile.