多结构物下穿上跨同一既有地铁盾构隧道变形控制研究——以深圳市岗厦北综合交通枢纽工程为例

Deformation Control of Multi-Structure Underpassing and Overpassing an Existing Metro Shield Tunnel:A Case Study of Gangxiabei Comprehensive Transportation Hub Project in Shenzhen,China

为解决既有地铁盾构隧道的上下层次先后进行工程建设带来的反复扰动变形大、结构开裂渗漏等一系列问题,指导设计合理的变形控制方案,以深圳市岗厦北综合交通枢纽工程为依托,下层次的暗挖电缆隧道十字交叉近接下穿采用预加固、辅助工程措施、开挖支护关键技术,上层次的地下商业空间平行上跨采用数值模拟不同降水深度、纵向分段跳舱长度、基底加固方案,并通过信息化监测探究上下层次进行工程建设对近接既有地铁盾构隧道的变形影响规律。研究结果表明:1)暗挖电缆隧道20 m范围内受扰动影响较大,可采用长度大于20 m的管棚预加固措施控制变形值。2)提高暗挖电缆隧道拱架的刚度和增加锁脚锚杆数量是降低既有地铁隧道变形的有效措施。3)预加固注浆压力宜控制在0.5 MPa,既有盾构隧道上浮在+2 mm范围内。4)上层次的地下商业空间平行上跨施工开挖至接近既有地铁盾构,大面积卸载在时空效应下会引发上浮变形突变,应缩短结构分段长度及暴露时间。5)降水施工应采取逐级降水达到既有地铁盾构隧道底部的深度,可合理平衡降水引起的土体固结沉降与土方开挖引起的隧道上浮。6)暗挖电缆隧道下穿扰动影响的30 m范围内,地下商业空间平行上跨施工对既有地铁盾构隧道产生的实际变形较数值模拟变形显著,且随着扰动距离增大对既有结构变形影响程度减小。

The construction of structures underpassing and overpassing an existing metro shield tunnel disturbs the existing structure repetitively,resulting in large deformation and crack leakage.Therefore,to address these issues and design a rational deformation control scheme,a case study is conducted on the Gangxiabei comprehensive transportation hub project in Shenzhe,China.Pre-reinforcement,auxiliary engineering measures,and key technologies of excavation and support are adopted for the mined cable tunnel at the lower level,and the numerical simulation of different precipitation depths,longitudinal segment sequence length,and basement reinforcement schemes are adopted for the parallel upper span of the underground commercial space at the upper level.Through informatized monitoring,the influence patterns of engineering construction on the deformation of adjacent existing metro shield tunnel is explored and validated.The results reveal the following:(1)The mined cable tunnel is considerably affected by the disturbance within 20 m,and the pipe roof pre-reinforcement measures with a length over 20 m can be used to control the deformation.(2)The effective measures to reduce the deformation of the existing metro tunnel are to improve the stiffness of the arch frame of the cable tunnel and increase the number of foot-locking anchors.(3)The prereinforcement grouting pressure should be controlled at 0.5 MPa,and the floating of the existing shield tunnel should be controlled within+2 mm.(4)The underground commercial space at the upper level is excavated in parallel to the existing metro shield,and the large-area unloading will cause a sudden change of floating deformation under the timespace effect.The length of the structural segment and the exposure time should be shortened.(5)The dewatering construction should be implemented step by step to reach the depth of the bottom of the existing metro shield tunnel,which can reasonably balance the consolidation settlement of soil caused by dewatering and the floating of tunnel caused by earthwork excavation.(6)The actual deformation of the existing metro shield tunnel caused by the parallel construction of the underground commercial space is more significant than that of the numerical simulation within the range of 30 m under the influence of the disturbance,and the influence on the deformation of the existing structure decreases with an increasing disturbance distance.