盾构近接施工对摩擦桩基承载性能的影响机制及控制技术研究

Mechanism of influences of shield construction nearby friction pile foundation on its bearing capacity and its controlling techniques

针对盾构近接施工对邻近摩擦桩基建筑物的扰动问题,基于盾构隧道开挖前后地层应力场的变化,建立了隧道-地层-桩基相互作用下既有摩擦桩基承载力解析计算模型,揭示了盾构近接施工对摩擦桩基承载性能的影响机制;以一地铁盾构隧道侧穿摩擦桩基老旧建筑物施工为工程背景,分析了盾构近接施工扰动下摩擦桩群的变形特征,论证了地层加固对控制邻近桩基变形的有效性。研究结果表明:隧道开挖后地层水平应力和剪应力的变化是影响摩擦桩基承载性能的根本原因,桩基承载力损失与隧道施工时的地层损失率呈正比;地层加固可有效控制隧道施工引起的地层损失,从而降低地层和既有桩基的变形,有效控制盾构近接施工时摩擦桩基建筑物的安全。

Aiming at the disturbance problem of the adjacent friction pile foundation buildings caused by shield tunneling,based on the changes in the stress field of the strata before and after shield tunneling,an analytical calculation model for the bearing capacity of the existing friction pile foundation under the interaction of tunnel,stratum and pile foundation is established,revealing the influence mechanism of shield tunneling on the bearing performance of friction pile foundation.Taking the construction of an old building with friction pile foundation at the side of a subway shield tunnel as the engineering background,the deformation characteristics of the friction pile group under the disturbance of shield tunneling are analyzed,and the effectiveness of ground reinforcement in controlling the deformation of adjacent pile foundations is demonstrated.The research results indicate that the changes in horizontal and shear stresses in the strata after tunnel excavation are the fundamental reasons affecting the bearing performance of friction pile foundations.The loss of bearing capacity of pile foundation is directly proportional to the loss rate of formation during tunnel construction.The ground reinforcement can effectively control the ground loss caused by tunnel construction,thereby reducing the deformations of the ground and the existing pile foundations.