With the continuous development of urban underground space construction, it is a common phenomenon to carry out foundation pit construction adjacent to existing tunnels. Excavation of foundation pit will destroy the original in-situ stress field, and then affect the adjacent tunnel, so it is necessary to study the corresponding measures. Based on this, this paper simplified the tunnel as Timoshenko beam acting on the Pasternak foundation, and established the calculation model of tunnel deformation caused by excavation unloading. Taking the deep foundation pit project of Hefei University City as an engineering case, the Plaxis 3D numerical simulation and theoretical model considering the characteristics of small deformation and strain were used for calculation respectively, and the two results were compared with the field measured data. The results show that the simulation results of Plaxis are basically consistent with the measured results, and the maximum deviation is only 0.5 mm, indicating that the constitutive model considering the characteristics of small deformation and strain can well reflect the stress and deformation of soil; In this paper, the calculated results considering the shear action of the tunnel are in good agreement with the measured results, and the calculated results of the analytical method are closer to the measured results than the simulation results, indicating that the proposed theoretical model can more accurately and effectively analyze the influence of the excavation effect on the deformation of the side-lying metro tunnel.

为了减小坑底隆起、支护结构过大位移以及增强稳定性,反压土和中心岛式开挖模式被广泛应用于深大基坑施工.文章采用数值模拟方法,以合肥大学城地下工程为例,研究了反压土和中心岛式开挖联合使用对支护结构、位移和稳定性的影响.研究表明,反压土和中心岛式开挖联合使用能大幅度减小各施工步支护结构的内力和基坑变形,通过设置三道斜撑,在其中预留反压土开挖来降低施工过程中引起的土体沉降,减少了开挖工序时支撑与反压土的相互干扰.采用此种方式可增强基坑整体稳定性,经济合理,施工效率较高,为深大基坑的施工提供参考借鉴.

通过有限元软件建立合肥大学城深大基坑三道支撑开挖三维数值模型,研究了开挖过程中周边隧道和支撑的应力和变形演变规律,并给出相应的控制策略和工程建议.研究表明,随开挖深度的增大,附近隧道同时发生上浮和向基坑方向的侧移两种位移,且基坑中部对应的隧道总位移最大.随着开挖的进行,附近隧道会同时发生向上位移和向基坑侧向位移两种位移,且基坑中部对应的隧道总位移最大,为保护地铁隧道等重要地下工程,建议在开挖前设置地下连续墙和挡土桩.

以某深基坑项目为例,利用小应变硬化模型对基坑开挖全过程进行模拟计算,结合坑外土体三维应力和隧道位移监测结果,研究基坑开挖对邻近既有隧道变形的影响.结果表明:土体三维应力和隧道变形计算结果与实测数据基本吻合,说明了计算模型的可靠性;基坑开挖引起围护结构向基坑方向最大偏移量为25.8 mm,引起邻近基坑地表最大沉降量为17.7 mm;基坑开挖引起左线隧道向基坑方向最大水平位移约为2.3 mm,向深度方向最大位移约为1.3 mm,与实测值基本吻合,符合规范要求;左线隧道管片最大轴力约为680 kN,最大弯矩约为58kN·m,隧道砌筑管片能够满足强度要求;基坑外不同位置的隧道在基坑开挖期间均向基坑方向偏移,竖向位移表现为上浮.

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