Study On Interaction Between Surrounding Rock And Supporting System Of Large Section Loess Tunnel

With the rapid development of China's economy,the construction of road network has gradually entered the provinces with less developed economies.During this period,the loess tunnel is often an important structure of the traffic line in the Liangzhu-Gully area,and the construction of the loess tunnel has steadily increased.The Menghua Railway is a railway coal transportation line from Mengxi to Central China.It is a major transportation infrastructure in China's “Twelfth Five-Year Plan”.There are 63 loess tunnels in the whole line,accounting for 27.6% of the total length of the tunnel construction.The deformation control effect of its loess tunnel is good.On the basis of this,through the convergence constraint method as the theoretical basis,the deformation characteristics of the surrounding rock of the large-section loess tunnel,the surrounding rock deformation control measures,the surrounding rock pressure characteristics,and the bearing characteristics of the supporting structure(initial support and secondary lining),got the following conclusion:(1)On the basis of literature and engineering case investigation,the displacement of the large-section loess tunnel of Menghua Railway is only 30%~50% of the large-section loess tunnel of Zhengzhou Passenger Dedicated Line,and its construction method and construction technology are further And analysis of processes and construction quality control.On the basis of the project,the finite element software is used to simulate the actual excavation process,and the deformation law of the arch under different working conditions is obtained.Combined with the numerical simulation results,the specific engineering application of the deformation control measures of the large-section loess tunnel is studied.Finally,The field monitoring data is analyzed,and the deformation law of large-section loess tunnel under space and time effect is obtained.(2)Through the field test,the surrounding rock pressure characteristics of the large-section loess tunnel under time and space effects are obtained.Through literature investigation and theoretical analysis,the surrounding rock pressure of the supporting project is obtained.The main reasons are: The measured surrounding rock pressure is the deformation pressure rather than the loose pressure.The theoretical calculation formula based on the loose medium balance theory is not suitable for the large-section loess tunnel.(3)Through the literature research system,the mechanism and mechanical properties of each component in the initial support structure are analyzed.The finite element software analyzes the large-section loess tunnel in the excavation under the condition of micro-step method and deformation control measures.The stress-bearing process of the initial support structure of the branch support,and the safety evaluation of the initial support structure by the calculation method of the concrete lining safety factor;Finally,the field test was carried out to obtain the force-bearing space of the shotcrete and grid steel frame.And the law of time distribution.(4)Through the field test,the spatial distribution characteristics of the secondary lining subjected to surrounding rock pressure,concrete stress and steel stress are obtained,and the initial support and secondary lining reinforcement and concrete stress are compared,indicating the mechanism of secondary lining..(5)Under the current technical level conditions,for the large-section loess tunnel: through the pre-supporting reinforcement of the surrounding rock and with the support of the initial support,the two together maintain the long-term stability of the tunnel,at this time,pre-complement The strong surrounding rock and initial support are the main body of the tunnel structure.The secondary lining structure is used as a safety reserve,embodying the design concept of “strong initial support and weak second lining”,which is in line with the design concept of the new Austrian law.