| It’s inevitably encountered in shallow buried and soft rock tunnel during the construction. By carrying out monitoring in the shallow buried and soft rock tunnel constructed with different methods including CRD, two-step and three-step, we studied ground surface settlement, stratigraphic layering settlement and initial support’s internal forces in Hejie Tunnel, then combined with FLAC3D to get the following conclusions:(1) By analyzing the measured data, we satisfied that the surface subsidence in shallow tunnels through soft rock ahead deformation stage-accelerating deformation stage-steady deformation stage, scale and impact distance of the settlement ahead of the excavation are mainly influenced by the span of excavating face; this paper also compared and analyzed the effect of different advancing reinforcement measures to rock deformation, it indicated that the surface jet grouting pile would made settlement reduced by55%, anti-slide pile has a very significant role in the control of the partial pressure, surface subsidence trough symmetrical to the centerline of the tunnel after reinforced with anti-slide; it’s of great significant to close initial support timely in weak rock tunnel; the relative settlement of stratigraphic to surface subsidence experienced preliminary stage-accelerated deformation stage-slow uplift phase-stabilized stage, which slow "uplifting" means that the ground deformation is under control.(2) By on-site monitoring, we satisfied that the self-bearing capacity of the overlying strata of shallow buried and soft rock tunnel is very weak, so early support-rock contacting pressure increase rapidly for its loose rock, and the pressure in the early stage of the construction approximately equal to full weight of the overlying soil column; in addition, rock excavation will lead to arch falling and then leading to the sudden change of internal forces of initial support concrete, it is a very bad thing.(3) By analyzing the test data on surrounding rock’s deformation law and rock-support contacting pressure, we knew the relationship between the real crown settlement and the contacting pressure, and we defined the reasonable range of ground’s settlement;(4) Based on the variable bit allocation principle, we simulated the tunnel construction constructed with various methods to obtain the ratio and value of rock deformation of different stages, then combined with the measured data, we realized the control of the crown settlement and optimized crown’s allowance settlement value, it not only ensured the lining’s thickness but also cut the construction cost sharply. |
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