隧道洞口段开挖面失稳模式及塌方演化机理

Failure Mode and Collapse Evolution Mechanism of Excavation Surface at Tunnel Portal Section

针对隧道洞口段开挖面失稳塌方问题,基于有限元极限分析法,从边坡自身的安全性出发分析隧道开挖对边坡的扰动影响,揭示隧道洞口段开挖面失稳塌方模式和机理,进一步分析台阶法施工以及管棚预支护措施对于隧道开挖面安全性的影响,验证隧道洞口段长大管棚施作的必要性。研究结果表明:考虑张拉剪切同步折减的边坡安全系数计算方法,能够真实模拟边坡的失稳;边坡安全性影响因素的显著性从大到小依次为边坡高度、黏聚力、内摩擦角和边坡角;隧道洞口段开挖面失稳塌方模式为典型的滑移式失稳塌方,在隧道开挖面前后位置分别形成滑移区和顶部塌方区;隧道洞口段管棚应能够穿过边坡的滑移线,采用60 m管棚超前支护,台阶法和全断面法施工进洞25 m时边坡安全系数分别为1.392、1.317,此时隧道和边坡安全得到有效保障。

Aiming at the instability and collapse of the excavation surface at tunnel portal section,based on the finite element limit analysis method,considering the safety of the slope itself,the disturbance effect of the tunnel excavation on the slope was analyzed. The instability collapse mode and mechanism of the excavation surface at tunnel portal section were revealed. The influences of bench method construction and pipe shed support measures on the safety of tunnel excavation surface were analyzed,the necessity of long and large pipe shed construction at tunnel portal section was verified. The results show that,the calculation method of slope safety factor considering the simultaneous reduction of tension and shear can truly simulate the instability of slope. The significance factors affecting slope safety from large to small are slope height,cohesion,internal friction angle and slope angle. The instability collapse mode of the excavation surface at tunnel portal section is the typical sliding failure mode,with a sliding area and a vault collapse area formed in the front and the back of tunnel excavation surface respectively. The length of pipe shed at the tunnel portal section should be able to pass through the slip line of the slope. With the advance support of 60 m pipe shed adopted,the slope safety factor is 1.392 and 1.317 using bench method and full section construction method when tunnel surface is 25 m far away from the tunnel portal. At this time,the safety of tunnel and slope is effectively guaranteed.