小净距隧道群下穿既有运营隧道离心模型试验研究

以深圳地铁7号线、9号线四条小净距隧道近距离下穿既有地铁1号线工程为研究背景,通过离心模型试验方法,分析了小净距隧道群施工对周围土体应力影响规律,揭示了盾构多次近距离穿越施工引起既有线变形及受力变化机理。研究表明:(1)小净距四线隧道开挖具有明显的"群洞效应",隧道群的形成会导致松动区扩大、土拱向上扩展,从而引起新建隧道承受竖向土压力增加;(2)既有隧道沉降随穿越次数的增多而增大,最终沉降为4次穿越叠加的结果,峰值位置基本位于4条隧道中心线正上方,盾构隧道每次穿越引起沉降增幅为13%~48%,穿越区域横向影响范围可达60 m以上;(3)新建隧道的开挖对既有隧道环向弯矩的影响不大,弯矩变化不超过10%,而对既有隧道纵向弯矩影响较大,随着穿越次数增加纵向弯矩明显增大,这也是隧道下穿施工引起纵向裂缝和渗漏水的主要原因。结合数值模拟计算进行对比分析,得到规律与试验相一致,进一步验证了试验结果对实际工程的可靠性。

Centrifugal model test of group tunneling with small spacing beneath existing tunnels

The existing metro line 1 in Shenzhen is under-crossed by four shield tunnels of metro line 7 and line 9 in close proximity. Based on the physical modeling of centrifuge tests, the influences on the stress of surrounding soil from construction of multiple tunneling in close proximity are analyzed. The deformation mechanism and stress characteristics of the existing tunnels induced by multiple under-crossing construction are investigated. The study shows that: (1) The group tunneling with small spacing can cause the ‘group-hole effect’ in the non-crossing region. The expanding of disturbed zones is the main reason for the soil pressure increasing above the new tunnels. (2) The settlement of the existing tunnels increases with each excavation process and reaches the final settlement as a result of four under-crossing superposition. The maximum settlement is above the center-line of four tunnels with the settlement trough width of more than 60 m. (3) The four shield tunnels in close proximity cause a significant increase in the longitudinal bending moment of the existing tunnels, while the circumferential moment changes a little. Therefore, segment fracture may appear after under-crossing construction. The test results are compared with the simulated ones, and they exhibit a similar change rule.