MECHANIC RESPONSE OF A SHALLOW-EMBEDDED AND DOUBLE-ARCH TUNNEL UNDER PARTIAL PRESSURES DURING CONSTRUCTION
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摘要:
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。
Abstract: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, (σy)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.
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Key words:
- 3D numerical simulation /
- partial pressure /
- vault displacement /
- plastic zone /
- stress concentration
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