| In recent years,with the rapid development of China's infrastructure construction,the proportion of high-stress soft rock tunnels is also increasing,and many problems are exposed in the construction of high-stress soft rock tunnels.For example,the deformation of surrounding rock is large.The deformation lasts for a long time,the initial support deformation is serious,the intrusion limit is easy to occur,and the shot top concrete is detached and broken.Therefore,how to safely and stably under high-stress soft rock conditions,to ensure the quality of the project has become a construction focus and difficulty.In this paper,based on the Weiwu high-speed Muzhailing tunnel as the project,the comprehensive analysis method of surrounding rock deformation measurement,theoretical analysis and finite element simulation is used to discuss the construction method of high-stress soft rock tunnel,so as to the Weiwu high-speed Muzhailing The construction method of the tunnel is optimized.The main work and achievements are as follows:(1)The creep model of high geostress soft rock is expounded.The mechanical mechanism of high geostress soft rock deformation is briefly analyzed.(2)Analyze the settlement and horizontal convergence of the arch of the Muzhailing tunnel in Weiwu Expressway by monitoring the measured data,combined with the existing high-stress soft rock tunnel engineering case and the same area Muzhailling railway tunnel to deform the high ground stress soft rock.The characteristics and internal and external factors of deformation are analyzed.The internal factors are: the characteristics of soft rock,the squeeze of high ground stress,water,etc;the external factors are: construction disturbance,excavation method and so on.(3)According to the actual situation of the Muzhailing Tunnel in Weiwu Expressway,different deformation control measures and optimization methods are proposed.In the aspect of deformation control measures,the three-dimensional finite element numerical simulation of the thickness of the shotcrete(21cm,28 cm,35cm)and the pre-reinforcement range(90°,127°,180°)in front of the face is controlled from the control of surrounding rock deformation and support.Structural stress,surrounding plastic zone and other aspects of comparative analysis;in the optimization of engineering methods,the excavation method(ring core excavation reserved core soil method,three steps seven steps reserved core soil method),step height(3m,3.5 m,4m),step length(5m,6m,7m),support timing(the timing of support is synchronized with the construction,the support timing is delayed,and the support time is delayed by two)The numerical simulation is carried out,and the deformation of surrounding rock,the force of supporting structure,the plastic zone of surrounding rock and the extrusion displacement of the face are compared.(4)Through numerical simulation,it is found that the stability of high-stress soft rock tunnel is closely related to the release of ground stress.Excessive stress release will increase the extent of the plastic zone.Once the plastic zone is increased,the strength of the surrounding rock will decrease rapidly and softening will occur.Therefore,excessive release stress will cause tunnel instability.(5)Propose reasonable deformation control measures and engineering optimization schemes,namely: three steps and seven reserved core soil methods,with 5m step length,3m step height,180° pre-reinforcement range,28 cm shotcrete thickness,support timing II(Deferred support),the combination is the best solution. |
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