考虑衬砌渗透性的盾构下穿既有隧道纵向结构错台变形研究

目前针对盾构开挖下穿既有隧道的解析理论研究一般基于Winkler地基模型，且未考虑既有隧道衬砌渗透特性，常常忽视地基剪切变形和既有隧道渗漏水的影响。基于体现土体剪切特性的Pasternak地基模型，首先计算了既有隧道渗漏水影响下盾构开挖在既有隧道轴线处产生的附加荷载。在此基础上，通过能量变分法建立由抗拉弹簧及剪切弹簧共同连接相邻管片环的既有隧道变形模型，获取隧道纵向结构剪切错台响应规律。选取多个工程实例，将理论解析结果与现场实测数据进行对比后发现，考虑地基剪切变形及既有隧道渗漏影响的理论解析结果更加贴近实测数据。此外，针对既有隧道异常渗漏区间渗漏程度、异常渗漏范围、异常渗漏位置进行了影响因素分析，并依据环间错台量及环间转角对既有隧道进行安全等级评估。通过参数分析发现：随着异常渗漏区间衬砌渗漏程度的增大，既有隧道纵向结构变形显著增大，当异常渗漏区间衬砌-土体相对渗透系数为0.1时，已有小范围环间错台量及转角被纳入安全评估等级Ⅲ；随着异常渗漏范围的扩大，既有隧道纵向结构变形增大，更大范围的环间错台量及转角达到安全评估等级Ⅲ；异常渗漏位置向远离新建隧道中心轴线方向发生偏移，既有隧道纵向变形逐渐减小，纵向结构变形峰值沿异常渗漏位置偏移方向发生偏移。

Dislocation Deformation of Existing Longitudinal Tunnel Structure Induced by Shield Tunneling by Under-crossing Considering Influence of Lining Permeability

At present, studies on shield tunneling under-crossing existing tunnels are generally based on the Winkler foundation model, and the permeability of the existing tunnel lining is not considered. The impacts of the shear deformation of the foundation and existing tunnel leakage are often neglected. Based on the Pasternak foundation model, which reflects the effects of shearing deformation of the foundation, the additional loads on the axis of the existing tunnel due to seepage and shield excavation were calculated. On this basis, an existing tunnel deformation model with a tensile spring and shear spring connected to the adjacent segment ring was established by the energy variation method to obtain the shear displacement response of the longitudinal tunnel structure. Several engineering examples were selected to compare the theoretical analysis results with measured field data, and it was shown that the theoretical analysis results considering the effects of the shear deformation of the foundation and the leakage of the existing tunnel are close to the measured data. In addition, the factors influencing the extent of abnormal leakage, abnormal leakage range, and abnormal leakage position were analyzed. The security level of the existing tunnel was evaluated according to the segment-joint rotation angle and dislocation displacement. Parametric analysis indicates that the larger the degree of leakage of the lining in the abnormal seepage zone, the larger the longitudinal structural deformation of the existing tunnel. When the relative permeability coefficient of the abnormal seepage zone was 0.1, a small range of the segment-joint dislocation displacement and rotation angle was included in evaluation grade Ⅲ. With the enlargement of the abnormal seepage zone, the longitudinal structural deformation of the existing tunnel increased, and the larger segment-joint dislocation displacement and rotation angle reached evaluation grade Ⅲ. As the abnormal leakage position shifted from the center of the existing tunnel away from the central axis of the new tunnel, the deformation peak value of the longitudinal structure deviated along the direction of the abnormal seepage position.