盾构开挖下邻近既有桩基的竖向响应分析

Vertical response analysis of adjacent existing single pile under tunneling

当桩顶作用有不可忽略的上覆外荷载时,通过桩身向周围土体传递的荷载必然会较大地改变桩周土体的应力状态,因此邻近隧道开挖引起的地层位移将会与自由场差别明显,为探究既有桩基在邻近盾构隧道开挖及桩基上覆荷载同时作用下的响应规律,结合两阶段法,通过引入Boxlucas1指数函数模型来描述桩土间的非线性作用,进而提出了在盾构开挖影响下,一种计算邻近既有桩基竖向响应的简化分析法,分析中考虑了当前研究中大都忽略的上覆外荷载作用,并分析了不同外荷载作用下的桩基响应规律。研究表明:当桩顶无荷载作用时,桩身轴力先增大后减小,最大轴力出现在隧道中心深度附近;当逐渐增加桩顶外荷载时,桩基下部的摩阻力先于上部到达极限,桩基轴力呈现出'先缓慢减小、再急剧减小、最后再缓慢减小'的'三段式'递减规律。

When the pile top is loaded, the load transmitted to the surrounding soil through the pile will inevitably change the stress state of the adjacent soil, so the displacement caused by tunnel excavation will be different from the free soil displacement field. To analyze the vertical response rules of the adjacent existing piles under the collective influences of tunneling and loads above pile, using the two-stage method, a simplified analytical method is proposed by introducing the model of BoxLucas1 exponent function to describe the nonlinear interaction between pile and soil, besides, the loads above piles are considered, which is ignored by the majority of the current researches. The results show that when there are no loads above pile, the axial force firstly increases and then gradually decreases along the pile, and the maximum axial force appears around the center of the tunnel by gradually adding loads above the pile. The skin friction of the lower pile will reach its limit earlier than that of the upper part. The axial force of pile foundation presents a 'three-stage' descending law of 'slowly decreasing, then sharply decreasing, and finally decreasing slowly'.