| Baiheqiao tunnel of Weiyuan Wudu section of Lanhai expressway is located in Longnan mountain of the West extension of Qinling Mountains.The main stratum of the tunnel body is sand gravel,and the stability of surrounding rock is poor.According to its engineering geological characteristics,code for design of highway tunnel(jtgd70-2004)and classification standard of surrounding rock of tunnel,the surrounding rock of baiheqiao tunnel is determined to be class V,which has typical characteristics of weak surrounding rock tunnel.The selection of its construction method and support structure is complex and special.Taking baiheqiao tunnel as the engineering background,based on the field investigation and practice in the past year,this paper adopts the method of combining theoretical analysis,numerical simulation and field monitoring to systematically analyze the support structure and surrounding rock stability.The main research work and results are as follows:(1)According to the engineering geological characteristics of the soft and broken surrounding rock of baiheqiao tunnel.based on the analysis of the deformation and failure mechanism of the surrounding rock of the tunnel and the design method of the support structure,it is proposed that the effectiveness of the advance support and the initial support structure is the key to control the long-term stability of the soft and broken surrounding rock tunnel in the construction and operation stages.The scheme of advance pre support(advance pipe shed,advance small pipe and r32n self-propelled hollow grouting anchor),the initial support scheme(hanging net shotcrete+steel support+primary formwork lining,etc.),the secondary support scheme and the mechanism of support structure are analyzed.(2)Using FLAC3D numerical simulation method,the paper analyzes the deformation convergence law of surrounding rock in different excavation stages and buried depth under the support structure of baiheqiao tunnel,and further evaluates the effectiveness of the support structure in controlling the deformation of surrounding rock.The results show that the vertical displacement and the horizontal displacement of the tunnel vault vary significantly in different excavation stages.The displacement of the upper and middle steps accounts for 80%?85%of the total displacement Value.(3)Based on the analysis of the displacement monitoring data of three typical sections,it can be seen that the rapid increase stage of tunnel displacement generally lasts for about 10 days,accounting for about 80%of the total convergence value,and is basically stable for about 30 days.The maximum vertical displacement and horizontal displacement are 26.84mm and 32.30mm,which are less than the allowable displacement value,indicating that the surrounding rock of the tunnel is stable,which further indicates that the tunnel adopts the The supporting structure and construction method are scientific and reasonable.Through comparative analysis,it can be seen that the prediction results of numerical simulation are close to the field monitoring results. |
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