| Underground space resources are widely developed and utilized in 21 st century.As a basic form of underground space utilization,tunnels play an important role in traffic road networks such as railways,highways and urban subways.As in recent years China has put forward sustainable economic development,tunnels and underground projects have become the pioneers in the field of transportation construction for their advantages in energy conservation and environmental protection.By the end of 2018,the total number of traffic tunnels operated in China reached 30,776,with a total length of 30,611 kilometers.Among them,there are 17,738 highway tunnels with a mileage of 17,236 kilometers,which is 24.4 times that of 2002,with an average annual growth rate of 700 kilometers.At present,China has become the country with the largest scale,the largest number and the fastest construction of tunnel construction in the world.With the accelerated pace of people's life and the advancement of science and technology,n the demand for safe,comfortable,fast,convenient and economical road transport methods is increasing.In response to the implementation of the sustainable development strategy,more and more single-hole with three-lane and four-lane tunnels have emerged.The construction of domestic super-large cross-section and super-span highway tunnels has entered a new era of development.In 2006,Shenzhen Nanping Yabao Tunnel was successfully completed,which was the first double-hole with eight-lane tunnel in China.Subsequently,some developed cities such as Guangzhou and Shenzhen successively built several double-hole with eight-lane highway tunnels.Compared with the two-hole four-lane and six-lane tunnels,the two-hole eight-lane tunnel has a larger section and a flatter shape with more serious stress concentration in the surrounding rock and support system,which makes the tunnel stability extremely poor.At present,some progress has been made in the construction technology of super-long span tunnels at home and abroad.However,levels of design,construction and disaster prevention and mitigation in long-span highway tunnels still need to be improved.Especially in the complex urban environment,there is still no mature and learnable experience in construction.In this paper,relying on the tunnel group project of Jinan Beltway Exressway and Jinan connecting line of Jinghu Expressway,we focused on the spatial evolution law of mechanical behavior of super-large section highway tunnel construction,the stability of surrounding rock and medium-clip rock wall of small clear section,and the control technology of surrounding rock deformation.Using field test,laboratory test,theoretical analysis,numerical simulation and model test,the mechanical response mechanism of the layered surrounding rock of large-span tunnel is studied in depth,and the construction method and construction parameters of the small clear section are optimized.We proposed the influence area of small clearance tunnel in super-large section and construction is and the control technology of surrounding rock deformation in the super-large section tunnel.A series of research results with theoretical and engineering significance are obtained,including:(1)Based on laboratory tests,the failure modes of horizontal and vertical laminated limestone samples are analyzed,and the anisotropic characteristics of horizontal and vertical two-dimensional physical and mechanical parameters of laminated limestone are revealed.The in-situ test of some mechanical parameters of layered limestone in tunnels is carried out.Combining with numerical simulation analysis of loading process,the in-situ test method is optimized and the test accuracy is improved.Formula method is used to estimate the lateral mechanical parameters of layered rock mass.Based on the estimated results and in-situ measured data,numerical inversion of two-dimensional parameters of layered rock mass is carried out,and the method to determine the mechanical parameters of horizontal layered rock mass is obtained,which provides a basis for the follow-up study of the mechanical parameters of horizontal layered rock mass.(2)Comparative analysis of tunnel surrounding rock deformation,support structure stress and plastic zone distribution characteristics under different excavation methods using full-section method,step method,CD method,semi-CD method and CRD method is studied.The reasonable excavation methods for different surrounding rock grades are determined:The stress of supporting structure of grade III surrounding rock tunnel tends to be stable for a short time,which is beneficial to chamber stability.Grade IV surrounding rock should be constructed by semi-CD method under shallow burial conditions,and 2-step method can be used for deep burial section to speed up construction progress,but arch support parameters should be properly strengthened during construction;The V-class surrounding rock section of the tunnel can be constructed by the CRD method;when the surrounding rock conditions are relatively good and there is no groundwater,the CD method can be considered to speed up the construction progress,but the system anchor must be well done to ensure that the surrounding walls of the two side are stable.(3)A calculation model for solving the plastic zone range of the middle-clipped rock wall in the double-hole tunnel is proposed,and finally the stability judgment process and steps of the middle-clipped rock wall are obtained.Based on the safety degree analysis,the construction proximity zoning of super-long-span and small-clear-distance tunnel is established.By means of numerical calculation and model test,the deformation characteristics and stress state of surrounding rock and middle-clipped rock wall of super-long-span and small-clear-distance tunnel are studied.The deformation law and overload failure law of surrounding rock during the construction of super-long-span tunnel with horizontally layered surrounding rock are revealed,and the blasting disturbance is analyzed.The stability of rock wall in small net distance tunnel with horizontal layered surrounding rock under action can provide reference for the design and construction of similar super-long-span tunnel projects.(4)The research on surrounding rock deformation control technology of super-large section tunnel was carried out,and management criteria of surrounding rock deformation during construction of super-long-span horizontal layered surrounding rock tunnels were proposed.The mechanical effects of tunnel cross-channel opening construction are analyzed,and the control measures,relevant support parameters and support schemes of tunnel cross-channel opening surrounding rock stability is proposed,which will have certain guiding significance for improving construction quality and progress and ensuring construction safety and the smooth passage of tunnels. |
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