考虑微拱效应的隧道管棚受力机制分析与支护效果评价

Mechanical behaviors and supporting effect evaluation of pipe roof in tunneling engineering considering micro-arch effects

考虑管间微拱效应、初期支护滞后效应、应力释放时空效应和基床系数变化特性,将管棚在轴向上划分为不同受力区段,建立深浅埋隧道管棚的力学理论模型,进而通过参数分析揭示管棚力学响应受影响规律。研究表明:(1)管棚在环向上表现为微拱效应,具有承载减跨效果,管棚外载为管间微拱转移的岩土压力;(2)管棚轴向上体现为长梁效应,发挥荷载传递作用,将超前围岩荷载传递至后方初支;(3)基于Pasternak弹塑性地基梁理论,推导了管棚挠度和内力的理论解,较既有理论解更贴近实测结果;(4)提出了围岩/初期支护承载比和管棚挠曲变形以量化评价管棚支护效果,为合理控制管棚变形并有效传递围岩荷载,软岩大跨隧道开挖进尺不得大于2m,拱顶附近30°范围内的管间距较其他部位应缩短5~10 cm。

Considering the micro-arch effects between the adjacent pipes, the delay effects of the initial support, the spatio-temporal effects of stress release of the surrounding rock and the coefficient change of subgrade reaction, the pipe roof is longitudinally divided into different sections. The corresponding mechanical model for the pipe roof is established both in the deep-and shallow-buried tunnels. Then, the mechanical response laws of the pipe roof are revealed through the parameter analysis. It is found that:(1) In the transverse direction, the pipe roof shows the micro-arch effects to bear the loads. The external loads on the pipe roof are the rock pressures transferred by the micro arches.(2) In the longitudinal direction, the pipe roof shows the beam effects to transfer the loads from the forward rock to the initial support.(3) Based on the Pasternak theory of elastic-plastic foundation beam, the analytical solutions for the deflection and the internal force of pipe roofs are derived, and the proposed theoretical solutions are more accurate than the existing theoretical ones.(4) The bearing ratio of the surrounding rock to the primary support and the pipe deflection are proposed to evaluate the supporting effects of the pipe proof quantitatively. To reliably control the deformation of the pipe roof and effectively transfer the loads of the surrounding rock, the excavation length of large-span tunnel should be limited in 2 m, and the distance between pipe roofs within 30° near the tunnel vault should be 5~10 cm shorter compared with that of other parts.