Determination of Stabilizing Forces Acting on Piles to Reinforce Slurry Trench against Globe Collapse

Concrete piles are used conventionally to reinforce slurry trench against global collapse during excavation in surrounding soft soil layers. In this paper, the stabilizing forces acting on piles were analyzed with the framework of the upper-bound approach of limit analysis combined with a rotational failure mechanism in undrained soil conditions. A trench without pile reinforcement was considered first, and the results obtained in the proposed approach agreed well with those obtained through the limit-equilibrium and variational limit-equilibrium closed-form solutions. It was shown that the trench has a deeper critical excavation depth as the stabilizing force provided by piles becomes greater. In addition, the critical sliding surface tended to be shallower with a decrease in the ground surcharge coupled with a surcharge near the edge of the trench. Finally, the required stabilizing forces were needed to increase rapidly to enhance the safety factor of the trench to 1.0. However, due to the reinforcement of slurry pressure and soil self-stabilization, the stabilizing forces were not always required at all excavation depths; only when excavation exceeds a certain depth could the reinforcing effect of piles be exerted.