| A large number of tunnels practice shows that if tunnel in the location such as fault fracture zone and its influence zone,or strong tectonic movement zone and in-tensely weathered zone in the shallow-buried section,or accumulation body section and loose sand body section above the tunnel,when it is excavated ,wall rock loose and fall off,produced a large amount of plastic deformation in a short time,extremely easy to damage in the form of discrete such as rib spalling,tunnel face instability,vault collapse,and other engineering disasters.However, for the present studies,it can not make perfectly reasonable explanation for the mechanical behavior in the loose bro-ken wall rock tunnel construction process.Therefore, it is necessary to simulate this type of tunnel excavation and support process, analyze its impact on the surrounding rock stability, and used to guide the construction.In this paper, with Du ye tunnel of Ji Huai Highway at K34 +200 ~ K34 +250 section,carry on related deformation and mechanical behavior for the shallow granular rock during the construction process,to provide a theoretical reference for design and construction of such tunnels.The main research work and conclusions are as follows:(1) Introduced the concept and characteristics of granula surrounding rock,analyzed the failure mode and stability characteristics of granula surrounding rock tunnel.Summarizes Construction methods commonly used and its characteris-tics,and analyzed the interaction mechanism of wall rock with supporting structure.(2) Made a small pipe grouting Physical Model Experiment,The results of the study show that the small pipe grouting supporting can significantly improve the mechanical properties of granular rock,enhance the bearing capacity of the surround-ing rock itself,reduce the settlement and deformation of the vault.(3)Proceed numerical simulation to different excavation and supporting process with rock engineering software FLAC3D,research the stability of granular rock of different construction methods.By comparing the results of numerical analysis, the excavation method using a large cross section will have a large disturbance at the granular rock and is not conducive to its stability,especially tunnel face emerge large inner vacancy displacement,the vault and surface subsidence is not easy to con-trolled.when used the excavation step by small cross section, such as CD method and CRD method excavation,the surrounding rock relatively stable,the vault and the sur-face subsidence is small,but the pressure surrounding support structure beared in-creased,and the construction process is complicated, construction progress is slow, the projects is high cost.When used the core of earth reserved steps excavation,we can reduce the disturbance of the surrounding rock,especially in the core soil effect the horizontal displacement of tunnel face surrounding rock is under controled,inhibit the vault and surface subsidence, the stress state of tunnel face significantly and the sta-bility of surrounding rock improved.As far as supporting measures be concerned,as a result of the poor stability of granular rock,if it isn't support advance, the excavated rock will emerge a large area of plastic yield,resulting in surrounding rock conver-gence deformation is too large or the overall unstable failure before initial support take effect. With advance support, the bulk mechanical properties of surrounding rock significantly improved and the overall strength improved,in the action range of ad-vance support, forming a stable load-bearing arch has a specified volume of resist compression effect,effectively improve the bearing capacity and stability of granular surrounding rock itself.(4) By analyzing the excavation monitoring results of the test section of the tunnel,it shows that using positive bench excavation method of reserved core soil for excavation,vault crown settlement is small,but using super-short bench method for excavation,vault crown settlement is large.Because of restrictions on the length of the core soil,horizontal convergence of the tunnel is bigger than another,accord with nu-merical simulation results. |
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