Study On The Construction Mechanics Behavior Of Widening Belt Of Soft Rock Highway Tunnel

In recent years,with the rapid development of economic construction in our country,the demand for transportation capacity is becoming more and more high,in order to meet the needs of economic development and the people travel,investment in roads and other infrastructure construction field in our country is becoming more and more big.In the process of highway construction,because of the impact of topography and geomorphology,the use of tunnel through the mountain becomes a common engineering requirement.The study of deformation and mechanical properties of surrounding rock and supporting structure during excavation is of great significance to guide safe construction.Based on Xuankou tunnel engineering,this paper combined the engineering geological characteristics,through the theoretical analysis and numerical simulation method,this paper analyzes the in widening with tunnel excavation process of variable cross-section,the change rule of displacement and stress of surrounding rock and supporting structure stress change rule,optimize the construction methods and steel supporting parameters,for future similar projects for reference.The main research contents and achievements of this paper are as follows:(1)Through the simulation of the whole construction process of Xuankou tunnel widening band,analyzes and sums up the cross-section of the changing law of stress and displacement of surrounding rock and initial support stress change rule,and the bearing capacity of surrounding rock is analyzed.Analysis results show that in the process of widening with excavation,average period of variable cross-section,primary support,stress and displacement of surrounding rock stress relative to the other section change is bigger,and on the left side of the arch waist,arch foot affected relatively more apparent on the right side,the reason is that the widening is mainly on the left side of the widening.By using the yield criterion to analyze the bearing capacity of surrounding rock,the results show that the surrounding rock is in a safe state.(2)When the tunnel was excavated with different steps,the displacement of the surrounding rock of normal section was gradually increased along with the increase of step length,and the stress release gradually increased.By using the yield criterion to analyze the bearing capacity of the surrounding rock of different steps,when the steps length is 6m and8 m,the surrounding rock is in a safe state during the whole excavation process,8 m is recommended for the step length.(3)With the increase of the footage,the displacement of the surrounding rock is gradually increased,and the stress release of surrounding rock increases gradually.Based on the analysis and comparison of the load-bearing capacity of different excavation,the surrounding rock is in a safe state when the excavation scale is 0.8m and 1.6m.In order tospeed up the construction progress and ensure the safety of construction,1.6m excavation is recommended.(4)By comparing the influence of different types of i-steel on the deformation of surrounding rock,it is concluded that the coordination relationship between the model and the spacing of the adjustment sections can better control the deformation of surrounding rock,and it is recommended to use 20 a i-steel in this tunnel,with a spacing of 0.7m.In conclusion,based on the actual project as the research background,theoretical analysis and numerical simulation of the soft rock highway tunnel widening zone of surrounding rock and supporting structure mechanics characteristics,the optimization and analysis of the construction method and the steel support parameters,these results can provide guidance for the design and construction of soft rock tunnel widening place.