浅埋偏压连拱隧道施工的力学响应分析

以江西某高速公路一浅埋偏压连拱隧道为背景,用MARC有限元程序对其出口段进行了动态施工的三维数值模拟。系统研究了塑性区分布和发展、拱顶下沉、正应力与剪应力的集中和转移、中隔墙竖向应力随施工过程的变化规律。研究表明:1.非对称开挖是引起中墙偏压的最关键因素,初衬和二衬的施作对改善中墙偏压作用不大,对称开挖才是最有效途径;2.在浅埋条件下,拱顶下沉有随埋深增大而增大的趋势,位移释放在开挖完成、支护之前就已经大部分完成。3.左右洞上台阶开挖后拱顶出现拉应力区,是易坍方部位,应超前或及时支护;4.由于偏压作用,山脊一侧边墙和中墙墙踵处塑性区更发育,该侧更易失稳;5.施工完毕,隧道两侧边墙附近集中的压应力转移到二衬和仰拱上,使二者成为应力集中部位,从而改善了隧道围岩的受力状况。

MECHANIC RESPONSE OF A SHALLOW-EMBEDDED AND DOUBLE-ARCH TUNNEL UNDER PARTIAL PRESSURES DURING CONSTRUCTION

Taking an expressway in Jiangxi province as the engineering background, the behavior of a shallow-embedded and double-arch tunnel with partial-pressure during construction is simulated.Several aspects, such as stress concentration and transfer, plastic zone distribution, vault displacement and change of vertical stress, (σ_y)of the mid-leading wall with construction are studied systemtically.The study indicates that:1) asymmetrical excavation is the key cause of partial pressure in the mid-leading wall and the construction of the first and second lining can not ameliorate the conditions greatly;2) under conditions of shallow embedment, vault displacement increases with embedment depth and displacement mainly happens during excavation of tunnel before lining construction;3)after excavation of the up-bench tunnel, pulling stress concentrates around the top arch and lining should be constructed promptly or beforehand;4)as a result of partial pressure, when plastic zones around the side-wall and mid-leading wall heel, which are near the mountain ridge, are better developed;and 5) when construction finished, compressive stresses at tunnel side-walls disappear and are transferred to the inverse arch and second lining, making them concentrated by shear stress and normal stress and improving the stability of the tunnel.