既有桩基在邻近盾构开挖下的水平向响应简化计算法

A SIMPLIFIED ANALYSIS METHOD FOR EVALUATING HORIZONTAL DEFORMATION OF ADJACENT EXISTED SINGLE PILE UNDER TUNNELLING

盾构隧道开挖不可避免地会对其邻近桩基产生扰动,因而准确评价桩基在邻近盾构开挖下的水平向响应具有重要意义。基于此,将基桩视为能考虑剪切效应的Timoshenko梁,然后利用两阶段法把盾构产生的附加荷载施加于基桩,建立起在Pasternak双参数地基上的Timoshenko梁的平衡微分方程,通过初参数解、传递矩阵法解出在任意附加荷载作用下的桩基水平向变形解。分析中考虑了当前大多忽略的基桩剪切变形,更符合实际工况,且当Timoshenko梁的等效剪切刚度为无穷大时,Timoshenko梁可退化为Euler梁。最后通过与三维边界元程序GEPAN计算结果的对比,验证了此方法的正确性。分析表明：桩基所受盾构扰动愈大,其剪切效应体现愈明显;剪切变形能够调整桩基内力分布,使得弯矩偏小,位移偏大。

The tunnelling will inevitably disturb the adjacent existing pile foundation,therefore,it is of great importance to accurately evaluate the horizontal response of pile foundation under tunnelling. Based on that,the pile foundation was regarded as a Timoshenko beam which could consider the shearing effect,and then using the two-stage method,the additional load generated by tunnelling was applied to the pile foundation to establish the equilibrium differential equation for the Timoshenko beam on the Pasternak two-parameter foundation. By using the solution of initial parameters and transfer matrix method,the horizontal deformation of pile foundation under any additional load was solved. During the analysis,the pile shear deformations which were overlooked in many cases were taken into consideration and were more in line with the actual conditions. And when the equivalent shear stiffness of Timoshenko beams was infinite,the Timoshenko beams could degenerate into Euler beams. Finally,by comparing with the the computing results by GEPAN,the correctness of that method was verified. The analysis results showed that the larger the disturbance to the piles under tunnelling,the more obvious the piles shear effect. The shear deformation could adjust the internal force distribution of the pile so that the bending moment was smaller and the displacement was larger.