暗挖车站零距离下穿既有隧道施工的应力分析

Stress Analysis of Underground-excavated Station Zero-distance Under-passing Existing Tunnel Construction

目的:某大断面平顶直墙暗挖地铁车站零距离下穿既有地铁矩形区间隧道施工,需分析施工过程对既有隧道的应力影响。方法:以零距离密贴下穿既有地铁矩形区间隧道的新建大断面平顶直墙暗挖地铁车站工程为背景,对洞桩法暗挖站工程施工进行设计;利用有限元分析软件建立有限元计算模型,对新建车站零距离下穿既有隧道的施工过程进行模拟分析,研究施工过程中既有隧道最大主应力、最大拉应力及最大剪切应力的变化规律及发生位置;进一步分析区间隧道混凝土结构塑性破坏区范围;比较应力监测值与模拟值的变化趋势及发生位置,通过拟合度来佐证了模拟的准确性和可实施性。结果及结论:随施工步骤进行,既有隧道结构最大主应力、最大拉应力及最大剪切应力均逐渐增大。根据实际监测结果,从步骤1到步骤5,三者增大幅度均很小;从步骤5到步骤6,三者分别突然增大到62.15、84.62、47.62 MPa,增大比例分别达315.0%、351.0%及378.1%;随后,三者分别缓慢增至68.75、89.61、51.03 MPa。既有区间结构底板区间b段靠近变形缝1处附近混凝土结构表面有微小裂纹变化。实际监测数据与模拟计算结果基本吻合。监测结果还表明,采取适当减缓施工进尺并及时进行支顶等措施,能有效防止既有结构混凝土表面裂纹的出现,进而对既有隧道起到保护作用。

Objective:In the construction of an underground-excavated metro station with large cross-section,flat roof and straight wall that under-passes the existing metro rectangular interval tunnel,it is necessary to analyze the stress impact of construction process on existing tunnel.Method:Taking the construction of a newly-built station similar to the above as research background,the construction of PBA(pile-beam-arch)method station project is designed.A finite element analysis software is used to establish a calculation model simulating and analyzing the above construction process of the newly-built station.The variation law and locations of maximum principal stress,maximum tensile stress,and maximum shear stress in the existing tunnel during the construction process are investigated.Furthermore,the range of concrete structure plastic failure zone of the interval tunnel is analyzed.The variation trends and locations of the stress monitored and simulated values are compared,and the simulation accuracy and feasibility are confirmed through goodness of fit.Result&Conclusion:With the progress of construction steps,the maximum principal stress,maximum tensile stress,and maximum shear stress in the existing tunnel structure gradually increase.Based on the field-monitored results,from step 1 to step 5,the increases in the above three are relatively small.However,from step 5 to step 6,they suddenly increase to 62.15 MPa,84.62 MPa,and 47.62 MPa,with increase ratios of 315.0%,351.0%,and 378.1%,respectively.Subsequently,they slowly increase to 68.75 MPa,89.61 MPa,and 51.03 MPa.Minor cracks and changes are observed on the concrete structural surface of the existing interval structure bottom plate segment b that is near the deformation joint 1.The field-monitored data is in good agreement with the simulation calculation results.The monitored results also indicate that adopting appropriate measures to slow down the construction progress and timely implementing supporting measures can effectively prevent the occurrence of cracks on the concrete surface of existing structure,thus protecting the existing tunnel.