盾构隧道施工对邻近承载桩基影响研究

Study of influence of shield tunneling on neighboring loaded piles

针对苏州轻轨1号线成层非均质土地基,选用Mohr-Coulomb弹塑性本构模型,建立三维有限元数值模型,研究非均质土中盾构隧道施工对邻近承载桩基工作性状的影响规律。数值计算结果表明,随着成层非均质土中各土层软硬程度差异的增大,隧道开挖会在邻近承载单桩引起明显反弯点,且桩体沉降亦随之增大;位于上软下硬成层土中的承载单桩桩身正弯矩更大,且该正弯矩出现在桩身中上部的反弯点部位,而上硬下软成层土中的承载单桩下部出现更大的负弯矩;与均质土中同位置承载单桩相比,位于上软下硬成层土中承载单桩桩顶及桩端轴力均更大,而位于上硬下软成层土中承载单桩桩顶轴力则更小。不同竖向集中荷载作用下,非均质土中盾构隧道开挖引起的承载群桩中前桩水平位移沿桩身分布与同位置承载单桩重合,后桩挠曲程度小于承载单桩;盾构隧道施工对承载群桩内力的影响明显高于对变形的影响。

By using Mohr-Coulomb constitutive model, a three-dimensional numerical model was established for layered non-homogeneous subgrade of Suzhou Light Rail Transit Line 1 ; and the influential law of tunneling on neighboring loaded piles were also studied. Based on the numerical simulation results, with the increase of difference between soft and hard strata of layered non-homogeneous subgrade, the inflection point appeared at the loaded single pile due to tunneling; and the pile settlement also increased. The upper part of the loaded single pile in upper soft and lower hard strata had larger positive bending moment; while the larger negative bending moment happened at the lower part of the pile disposed in upper hard and lower soft strata. In contrast to the loaded single pile in homogeneous subgrade at the same position, there was larger axial force presented to pile top and pile tip of the loaded single pile in upper soft and lower hard strata; but the smaller axial force occurred at pile top of the loaded single pile in upper hard and lower soft strata. The horizontal displacement distribution of the front pile in loaded pile group which beared different concentrated loads coincided with the loaded single pile at the same position; while the deflection of the back pile was less than the loaded single pile. Besides, the influence caused by excavation of shield tunnel in layered non-homogeneous subgrade to the internal force of loaded oile group was more significant than the deformation.