南京富水松软地层新建盾构隧道穿越引起的既有隧道工程安全等级划分

Engineering Safety Level Classification of Existing Tunnel Disturbed by Newly-built Shield Tunnel Crossing Water-rich and Soft Stratum in Nanjing

为定量评估既有地铁盾构隧道受穿越施工扰动后的结构安全状态与服役性能,采用MIDAS软件建立了新建盾构隧道穿越既有盾构隧道的三维数值模型。通过调整隧道间的竖向净距,对南京地区以富水砂层、软土层为主的松软地层条件下的盾构隧道穿越施工引起的既有隧道的竖向位移响应进行了定量研究,并根据隧道的力学衰减特性分析了既有隧道的安全等级。结果表明:盾构隧道下穿、上跨施工引起沿既有隧道纵向土体的沉降曲线分别呈“W”型、“M”型,相同地层条件下上跨施工引起的既有隧道变形的绝对值比下穿施工小;南京富水砂层、软土层新建隧道穿越引起既有隧道沉降半槽范围分别约为3.5倍与5.0倍隧道外径;结合既有隧道力学性能衰退特征,以隧道纵向差异变形量作为指标将盾构隧道穿越工程划分为微弱影响、一般影响、显著影响、强烈影响等四类;根据数值模拟和历史变形数据,预测了南京地区3个典型的盾构隧道穿越工程施工完成后既有盾构隧道的竖向差异变形量,据此计算了相应的影响等级及其同等级下的竖向变形余量。

To quantitatively evaluate the structure safety status and service performance of existing metro shield tunnels after being disturbed by crossing construction,a 3D numerical model of newly-built shield tunnel crossing existing shield tunnels is established by MIDAS software.By adjusting the vertical net distance among tunnels,a quantitative study is conducted on the vertical displacement response of existing tunnels caused by shield tunnel crossing construction under conditions of soft soil strata which is mainly composed of water-rich sand and soft-soil formation in Nanjing region,and based on the mechanical attenuation characteristics of the tunnel,the safety level of the existing tunnel is analyzed.The results show that:the curves of soil mass settlement along the existing tunnel longitudinal direction caused by shield tunnel under-crossing and over-spanning construction are′W′type and′M′type respectively,and under the same stratigraphical condition,the absolute value of deformation of the existing tunnel caused by over-spanning construction is smaller than that caused by under-crossing construction;the half-groove range of the existing tunnel settlement caused by the water-rich and soft stratum in Nanjing is approximately 3.5 times and 5.0 times the outer diameter of the tunnel respectively.Based on the characteristics of existing tunnel mechanical performance attenuation,the shield tunnel crossing engineering is divided into four categories using the tunnel longitudinal differential deformation as an indicator:weak impact,general impact,significant impact,and intense impact.Based on numerical simulation and historical deformation data,the vertical differential deformation of existing shield tunnels after the completion of three typical shield tunnel crossing projects in Nanjing region is predicted,according to which the corresponding impact level and vertical deformation allowance at the same level are calculated.