| “One Belt and One Road” is one of the important development strategies proposed by China in recent years.The implementation of this strategy has played a powerful role in promoting the economic development in the central and western regions of China.Economic development is inseparable from economic and trade exchanges.Economic and trade exchanges in various regions are built on the basis of unimpeded traffic.In the middle and western regions of China,there are many mountains and the geological conditions are extremely complex.In the course of getting through the traffic lines,it will inevitably encounter a lot of difficulties.Bridge tunnel engineering problems.Deep soft rock tunnels are often encountered during the construction of expressways and railways.Since these tunnel works are often under high ground stress and deep-buried conditions,and the soft-rock stability is extremely poor,plasticity is prone to occur during the construction process.Deformation shows obvious rheological characteristics,and large-scale deformation of tunnel surrounding rock occurs from time to time.In the high-stress soft rock tunnel project in recent years,it is urgent to seek a support plan that is both reasonable,effective,and economical to solve the engineering problems.This paper relies on a highway soft rock tunnel project in the northwest of China,and uses the high-stress deep-buried weak rock tunnel deformation segment as the research object.The following research work was carried out:(1)Analyze the deformation mechanism of soft rock under high ground stress conditions,and point out that the mechanism mainly includes two kinds of extrusion deformation and expansion deformation.According to the actual situation of the large deformation stage of surrounding rock in the construction process,the large deformation of surrounding rock is proposed.The seven major factors are internal factors including the initial geostress field of the tunnel,the buried depth of the tunnel,the ratio of strength to stress of the surrounding rock,and the mechanical and structural characteristics of the surrounding rock.External factors include size effect,unloading mechanical effect,and construction methods.Wait.(2)Conduct on-site monitoring and measurement of the supporting project.By analyzing the displacement monitoring data and stress monitoring data of tunnel surrounding rock andinitial support structure,it can be known that the tunnel's maximum headroom convergence value is 702 mm,and the maximum dome settlement value is 1232 mm.As the deformation is too large,the initial support structure is destroyed,and a serious intrusion phenomenon occurs;the maximum rock pressure is 1.03 MPa,and the maximum stress of the shotcrete is about24 MPa,which is close to the compressive strength value of the C25 shotcrete design.It can be seen that the cracking and falling of the sprayed concrete occur.According to the monitoring data,serious serious deformation disasters have occurred in the tunnel.(3)Three-dimensional numerical simulation of the three-step seven-step method and the CD method are performed using finite element software ABAQUS,and the support parameters and excavation method are used to analyze the clearance of the high-stress soft rock tunnel,the dome settlement,and the surrounding rock mass.The influence of rock pressure and the plastic zone of surrounding rock indicates that the supporting effect of system bolts in soft rock tunnels is not ideal.In comparison,the locking foot bolts can play a greater role in the stability of steel frames.To a certain extent,the deformation of surrounding rock can be controlled.At the same time,comparing the 12 working conditions of the three steps,seven steps and CD method,the reasonable supporting parameters of the two methods are given.(4)Comparing and analyzing the two conditions with the best support under the three steps,seven steps method and CD method,and pointing out that when using the CD method,due to the presence of the septal wall,the soft surrounding rock can be controlled more effectively.The deformation of the tunnel,and put forward more reasonable support parameters to solve the problem of large deformation of the tunnel surrounding rock in the construction process. |
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