隧道开挖影响下地层-基础体系的接触力学响应分析

CONTACT MECHANICAL RESPONSE ANALYSIS OF SOIL-FOUNDATION SYSTEM UNDER THE INFLUENCE OF TUNNEL EXCAVATION

针对隧道正交下穿既有结构施工力学响应的预测问题,建立了考虑多体接触作用的隧道施工扰动下地层-基础体系力学响应解析预测方法.该方法将地层视为均匀各向同性的线弹性体,通过引入接触理论考虑地层与基础间的接触作用,并提出"隧道开挖与基础作用换序求解"的新解析思路,确定了最终状态接触压力,解决了隧道开挖及多体接触耦合作用下接触压力难以确定的问题,进而依据弹性力学解的叠加性获得目标问题的解析解答.通过对比该解析解与ABAQUS数值解,发现两者吻合良好.基于本方法开展参数分析,研究了地层参数、隧道埋深、隧道边界径向位移以及外荷载集度对地表竖向附加位移、接触压力和基础内力分布的影响规律.结果表明:本方法可准确预测地层-基础体系的接触力学响应,实现了地层与基础间接触力学行为的量化描述;地层杨氏模量和泊松比对地层-基础体系力学响应的影响分别侧重于变形和受力,而隧道埋深和隧道边界径向位移变化对受力变形均有较大影响;地层位移受隧道开挖扰动与多体接触效应的耦合作用,且接触影响范围局限在接触区域附近;隧道开挖使接触压力产生"中间释放、端部集中"的重分布现象,并由此造成基础内力的大幅增长.当开挖扰动剧烈时,甚至产生竖向位移不连续的脱空接触现象.研究成果对城市浅埋隧道施工影响下地层-基础体系力学响应预测具有重要的理论意义和应用价值.

To realize the theoretical prediction for mechanical response of soil-foundation system due to new tunneling below, an analytical method for the mechanical response of the soil-foundation system under the disturbance of tunnel construction is established, considering the multi-body contact effect. In this method, the stratum is regarded as a homogeneous isotropic medium with linear-elastic property. Next, the contact theory is introduced into the derivation process to consider the contact effect between stratum and foundation, and a new analytical strategy,“exchanging the sequence between tunnel excavation and foundation action”, is proposed to determine the analytical expression of contact pressure in final state. Then, the difficulties of determining the contact pressure under the coupling action of tunnel excavation and multi-body contact are overcame. Finally, the proposed solution is obtained using the superposition of elasticity solution. The analytical results are in good agreement with the numerical results, which verifies the correctness of the analytical solution. Based on the proposed solution, the effects of stratum parameters,tunnel depth, radial displacement of tunnel boundary and external load concentration on the vertical displacement increment, contact pressure and internal force distribution of foundation are analyzed. The results show that the analytical method can accurately predict the mechanical response of the soil-foundation system, and it can realize the quantitative description of the complex contact mechanical behavior between the stratum and foundation. The effects of Young’s modulus and Poisson’s ratio of formation focus on deformation and stress respectively, while the variation of tunnel buried depth and radial displacements along the tunnel boundary lead to significant changes in deformation and stress. The ground displacement is the result of the coupling effect of tunnel excavation and multi-body contact, and the significant impact region is limited near the contact area. Under the influence of tunnel construction, the contact pressure will redistribute, which is characterized by “release in the middle and concentration at the end”. As a result, the internal force of foundation is found to increase greatly, and when the disturbance of tunnel construction is severe, it may even lead to incomplete contact phenomenon with discontinuous vertical displacement. The research has important theoretical significances and application values for the prediction of mechanical response of soil-foundation system caused by the construction of urban shallow tunnel.