深基坑开挖卸荷对既有桩基侧摩阻力影响分析

基坑开挖卸荷导致工程桩桩侧极限阻力降低.建立单桩模型,用Mindlin应力解考虑开挖引起的竖向有效应力变化,分别计算开挖前后的桩侧极限阻力.通过某工程案例,将理论结果与其他结果相对比.最后分析了桩侧阻力降低系数随基坑开挖深度、边长、长宽比及桩长的变化规律.结果表明:桩侧阻力降低系数随开挖深度增加先减小而后缓慢增大,存在谷值临界深度,随开挖边长、长宽比增加先减小而后趋于稳定;增加桩长导致桩侧阻力降低系数增大.

Effect of Unloading on the Shaft Resistance of Existing Piles due to Deep Excavation

The effect of excavation-related unloading on the underlying soil will reduce the ultimate pile shaft resistance. In this study, Mindlin's stress solution was used to allow for the variation of vertical effective stresses induced by excavation around a single pile. The ultimate resistances of the pile shaft before and after the excavation were calculated. The results of theoretical calculation were compared with others through a case study. Furthermore, the variations of reduction factors for shaft resistance with excavation depth, excavation length, ratio of length to width and pile length were analyzed. The results showed that reduction factors for shaft resistance decreased firstly and then increased with the increase of excavation depth, and it decreased first and then tended to be stable with the increase of excavation length and ratio of length to width. With the increase of pile length, the reduction factors for shaft resistance increased.