| Since the reform and opening up,the highway and railway tunnels in China have experienced rapid development.The proposal of "Build China into a Transportation Power" strategy in the new era has pushed the transportation industry into a new stage,and put forward higher requirements for the utilization form and construction technology of underground space.Twin-arch tunnel,a large-span tunnel structure,is designed to meet the special construction needs during the rapid development of highway tunnels.It is characterized by smooth alignment,small floor area and high space utilization ratio.Compared with the traditional separated or small-spacing tunnels,twin-arch tunnel has significant advantages in line connection,adaptability to various terrains and environmental protection.However,due to the large excavation span and the interaction between the left and right tunnel,the surrounding rock is disturbed frequently and the load conversion of supporting structures is extremely complex and changeable,which contributes to the increasing difficult in tunnel stability control.Twin-arch tunnel of Xiamen Second West Passage represents one of the most technically challenging projects in China.Its double-line span is 45.7 m,the shallowest buried depth is only 5.6 m,and the largest single tunnel cross-section is up to 257.2 m2,which represents the largest excavation of twin-arch tunnel in the world.This thesis applies the twin-arch tunnel as the case project to study the construction deformation control technology of ultra-shallow-buried twin-arch tunnel with super-large cross-section under complex conditions.Literature research,field testing,theoretical analysis,numerical simulation and field monitoring were applied during the research.The specific contents and main conclusions are as follows:(1)Grouting reinforcement in advance is the prerequisite of deformation control for super-large cross-section tunnel construction under complex geological conditions.It studied the technology of one-off grouting through the full hole for advance reinforcement of composite strata by controlling the grouting area of cross-section control in composite strata.The mechanism of different grouting forms is analyzed and the common used grouting technology as well as its applicable strata is discussed.The twin-arch tunnel grouting form and grouting scheme are proposed.The grouting material,slurry ratio,and grouting parameters are determined.The grouting parameters includes reinforcement scope,grouting pressure,grouting amount,grouting rate,the distance of grout diffusion,the arrangement of grouting holes and the thickness of grout retaining wall.The analysis method and drilling inspection method are used to evaluate the grouting reinforcement effect,and a complete technological process of full hole one-off grouting technology for advance reinforcement of composite strata by controlling the grouting area of cross-section is summarized.(2)Excavation by stages and headings is the central part of deformation control for the construction of ultra-shallowly-buried tunnel with super-large cross-section.It studied the optimization of the excavation process of the ultra-shallowly-buried twin-arch tunnel with super-large cross-section.Combined with numerical simulation and field monitoring,the surrounding rock deformation and structure stress of two excavation schemes are analyzed,and the final scheme was determined by considering surrounding rock stability,structural safety,and construction duration.The three-dimensional numerical simulation of tunnel-entering and-exiting is carried out,and the cross passage stability is evaluated by analyzing the surrounding rock deformation and the structure stress.The results show that the structural stress of cross passages and the deformation of the surrounding rock both satisfy the safety control requirement,and the stability of the surrounding rock is well controlled.(3)Reasonable support parameters and support time are the key to control the deformation during the super-large cross-section tunnel construction.It studied the optimization of the supporting system of ultra-shallowly-buried twin-arch tunnel with super-large cross-section.The interaction principle between the tunnel supporting structure and surrounding rock is analyzed,and the design concept of the supporting structure is summarized.Based on the numerical simulation,the initial support parameters are optimized and the stress release ratio of surrounding rock in different construction stages is investigated according to the analysis of surrounding rock deformation and structure stress.Based on the fitting processing and regression analysis of the vault settlement measurement data,and combined with the optimization results of stress release ratio of surrounding rock,the reasonable supporting time of the second lining of twin-arch tunnel is determined.(4)Reasonable step-by-step control standard and fine control measures are the basis and guarantee for quantitative deformation control during super-large cross-section tunnel construction.It studied the strata deformation regularity and the step-by-step control standard of ultra-shallowly-buried twin-arch tunnel with super-large cross-section.The three-dimensional numerical simulation of the twin-arch tunnel construction is carried out.Combined with the simulation results and monitoring data,the surrounding rock deformation and ground settlement are analyzed.The dynamic relationship between the ground settlement and key construction steps is established.Based on the principle of displacement distribution,the overall control objective of the strata deformation is assigned to each construction stage,and the step-by-step control standard was derived,which realizes the fine control of the whole process of disturbance deformation during twin-arch tunnel construction.The multi-steps and-stages deformation control measures taken during the twin-arch tunnel construction is summarized. |
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