Study On Construction Technology And Surrounding Rock Deformation Control Measures Of Large Section Tunnel In Red Bed Geology

With the rapidly development of national transportation construction,there are more and more large-section highway tunnels.For three-lane highway tunnels with large cross-sections and large excavation sections,the structural stress is more complicated,and engineering disasters such as large deformation,collapse,and cracking of the lining structure often occur.In order to ensure the safety of construction,a large-section tunnel under complex geological conditions needs to be systematically studied in combination with the actual engineering for its excavation method and surrounding rock stability.In this paper,the key construction technologies of large cross-section highway tunnel are analyzed and studied by numerical simulation and on-site monitoring and measurement based on the project of Shangchongqing tunnel of Yishi highway in Yunnan Province:(1)This paper systematically summarizes the geological age of the formation of red beds in central Yunnan,its distribution area in China,structural characteristics and engineering properties,and briefly introduces the geological overview of relying on the project-Shanchongqing Tunnel.(2)The numerical simulation method was used to simulate the construction stability of the grade IV surrounding rock section of the Shanchongqing Tunnel under four different excavation methods including the full-section method,the step method,the three-step method,and the cross-middle partition method.Under different excavation methods,the deformation of surrounding rock,the stress of spray-mixed structure,the stress of anchor structure,the range of plastic zone of surrounding rock,and the advantages and disadvantages of various methods are comprehensively compared and analyzed.It is recommended that the step IV of the surrounding rock section of Shanchongqing tunnel be adopted Method construction.(3)Six sets of working conditions with different step heights(4m,4.5m,5m,5.5m,6m,and 6.6m)and four sets of working conditions with different step lengths(6m,8m,10 m,and 12m)were developed.The excavation parameters(step height and step length)of the method were optimized.Based on the numerical simulation results and comprehensive comparison and analysis from the aspects of surrounding rock deformation and supporting structure stress,it is recommended that the height of the upper step of the IV rock section of the Shanchongqing tunnel be 6.6m and the length of the step be 6m.(4)The numerical simulation method was used to simulate the construction stability of the V-level rock section of the Shanchongqing tunnel under three different excavation methods,such as the three-step method,the cross-middle partition method,and the double-side guide method Under different excavation methods,the surrounding rock deformation,the stress of the mixed structure,the stress of the anchor structure,the range of the plastic zone of the surrounding rock,and the advantages and disadvantages of various methods are comprehensively compared and analyzed.Step method construction.(5)Based on the monitoring and measurement data of the grade IV surrounding rock section and grade V surrounding rock section of the Shanchongqing tunnel,the changes of the surrounding rock deformation,the surrounding rock stress and the axial force of the steel arch are analyzed.A comparative analysis was carried out to verify the rationality of the construction scheme adopted in the IV and V surrounding rock sections.