| From the 1980 s to the end of 2020,China completed 12412 tunnels with a total length of approximately 17621 km,marking the official entry of China’s railway construction technology into a period of rapid development.However,currently there are still a series of technical difficulties in tunnel construction caused by long excavation lengths,large construction sections,and complex geological conditions.In view of this,this article relies on the Zhongwei-Lanzhou Railway project of China Railway Beijing Engineering Bureau Group Co.,Ltd.(ZLZQ-2-QT-(2021)-026),selects the test section for geological feature extraction and analysis,and based on this,conducts model experimental design and numerical simulation modeling.By combining multiple methods,the deformation mechanism of the tunnel face during excavation using the three step method is analyzed,and the reasons for the deformation of the tunnel face during tunnel construction are analyzed in detail,Select reasonable support methods based on the deformation situation and analysis results,and compare and study the effect of advanced reinforcement.The obtained results have improved the ability to identify and prevent tunnel deformation under similar geological disaster conditions,laying a foundation for the evaluation and prevention of tunnel surrounding rock deformation,and ensuring construction safety.The main work and conclusions of the article are as follows:(1)Collect and organize the overall geological overview and on-site construction situation of the tunnel site area,select the section DK43+925～DK44+000 of Xiangshan Tunnel as the experimental section,and extract and analyze the geological characteristics of the experimental section.It is believed that the deformation of the tunnel face is caused by multiple factors together.(2)Based on the lithology of the experimental section,an orthogonal ratio test was conducted to determine the soil material and similarity ratio.Model tests were designed using a simulated on-site excavation method to conduct research on the deformation mechanism of the tunnel face.After excavation of each step,it was found that the maximum axial stress always appeared at the top and bottom of the deepest excavation face.The maximum vertical stress initially appeared at the top and bottom of the upper step face,and then shifted from the center to the bottom.(3)Based on model experiments,numerical simulation modeling and calculations were conducted,with a focus on analyzing the extrusion deformation of the palm face and its impact on the soil ahead,as well as the deformation impact and soil stress changes during step excavation.After excavation of each step,it was found that the maximum axial stress always appeared at the top and bottom of the deepest excavation face.The maximum vertical stress initially appeared at the top and bottom of the upper step face,and then shifted from the center to the bottom.(4)Based on model experiments and numerical simulation results,the deformation mechanism of the tunnel face was summarized and analyzed.It was found that the deformation of the tunnel face is caused by the high self weight stress of the deep buried tunnel,which releases stress during excavation and leads to rock deformation.Under the action of groundwater,the strength of the rock mass is reduced,and these factors are coupled and formed together.(5)A comparative experiment was conducted on excavation using two methods: small conduit support and anchor rod support.By comparing and analyzing the deformation phenomenon of the face under different support methods,extrusion displacement values,and changes in soil pressure response at each measuring point,the reinforcement effect was analyzed.Strain sensors were installed on specific anchor rods to study the parameter characteristics of the anchor rods themselves.It was found that the reinforcement effect was best under anchor rod support conditions. |
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