基坑开挖引起邻近既有隧道变形的影响区研究

Influenced zones for deformation of existing tunnels adjacent to excavations

既有隧道会因邻侧基坑开挖卸荷产生变形,对隧道正常使用和安全产生影响,其变形控制至关重要。基于大量工程案例资料,以天津市某邻近既有隧道深基坑实测资料为基础,采用考虑土体小应变刚度特性的有限元方法对基坑施工对坑外既有隧道变形影响规律进行了参数分析,结合不同规范变形控制标准,划分了不同围护结构变形模式和最大水平位移条件下坑外既有隧道变形影响区。研究结果表明,坑外变形影响区大致可简化为直角梯形形状。根据实际工程基坑围护结构可能产生的变形形式、最大变形和隧道与基坑的相对位置,可根据该影响区预估隧道可能产生的变形。围护结构变形模式和变形控制值相同条件下,变形影响区范围随着围护结构最大水平位移增大而增大;围护结构最大水平位移和变形控制值相同条件下,围护结构悬臂型变形模式下变形影响区范围最小,内凸型和复合型次之,踢脚型最大。

The unloading effect of excavations can cause deformation of the adjacent existing tunnels, which may seriously influence the operation and safety of the tunnels and hence should be strictly controlled. Based on the field measurements of a project in Tianjin and a large number of case histories, the finite element method considering the small strain of soil is adopted to conduct parametric studies on the relationship between the deformation of the existing tunnels and the excavation construction. According to various deformation controlling criteria for the existing tunnels, the retaining side of excavation is zoned with different deflection modes and maximum horizontal displacements of retaining structures. It is shown that the influenced zone can be simply characterized by a right trapezoid, which can be used to predict the deformation of the existing tunnels approximately according to the relative locations of the tunnels, deflection modes and maximum horizontal displacements of retaining structures. For a given deflection mode of the retaining structures and a deformation controlling criterion, the influenced zone expands as the maximum horizontal displacement of the retaining structure increases. Under the same criteria and maximum horizontal displacement of the retaining structures, the range of the influenced zone increases with the variation of deflection modes in the order of cantilever type, convex type, composite type and kick-in type.