大跨度双连拱隧道下穿既有地铁近接施工的围岩力学特征模型试验研究

Model test study on mechanical characteristics of surrounding rock of long-span double-arch tunnel underpassing existing subway close-spaced construction

以西安沣河东路市政通道工程下穿地铁5号线区间既有地铁结构为工程背景,采用模型试验和有限元数值模拟相结合的方法研究大跨度双连拱隧道下穿既有地铁结构近接施工的力学特征响应过程。结果表明:随着大跨度双连拱隧道开挖,地表沉降呈现“缓慢增加—急剧增大—趋于稳定”3个阶段;中隔墙处对应地表沉降值最大,对此处的地表变形应加强监测,及时控制;拱顶竖向应力变化也呈现“应力聚集—应力释放—稳定状态”3个阶段,且会在一定范围形成压力拱来承担上部荷载;边墙所受开挖扰动比拱顶大,边墙竖向应力集中及水平应力释放主要在0.3倍~0.5倍单洞开挖跨度范围内,对此部分围岩应及时注浆加固处理;通过试验和数值计算得到U型槽轨道板上下表面应力曲线形状均呈“W形”和“倒W形”,且轨道板最大沉降和翘曲出现在-0.9D~0.9D(D为隧道单洞开挖跨度)处,此处会出现最大拉压应力;此研究成果为本隧道的设计和施工提供了理论依据,同时对今后类似工程的施工提供了良好的借鉴和参考价值。

Based on the existing subway structure that underpassing the section of metro line 5 of Fenghe east road municipal passageway project in Xi an as the engineering background.The model test and finite element numerical simulation were used to study the mechanical characteristic response process of underground double-arch tunnel.The results show that with the excavation of long-span double-arch tunnel,the surface settlement presents three stages of slow increase,sharp increase and tend to be stable,and the corresponding surface settlement value is the largest at the middle partition wall,which should be strengthened monitoring and timely control of surface deformation.The change of vertical stress in vault can also present three stages of stress accumulation,stress release and stable state,and the pressure arch will be formed in a certain range to bear the upper load.The amplitude of excavation disturbance of the side wall is larger than that of the vault.The vertical stress concentration and horizontal stress release of the side wall are mainly in the range of 0.3 times to 0.5 times the span of single hole excavation.Therefore,some surrounding rocks should be reinforced by grouting in time.The test and numerical calculation results show that the stress curves of the upper and lower surfaces of the U-groove track plate are“Wshaped”and“inverted W-shaped”,and the maximum settlement and warping of the track plate appear at-0.9 D to 0.9 D(D is the single tunnel excavation span),where the maximum tension and compression stress occurs.The research results provide a theoretical basis for the design and construction of the tunnel,and also provide a good reference value for the construction of similar projects in the future.