| The time and space effect of the deformation law of surrounding rock during tunnel excavation is obvious.The coupling between the dynamic excavation process of the tunnel and the rheological characteristics of rock mass has a great influence on the stability of surrounding rock and tunnel structure.The dynamic excavation of the tunnel is closely related to the construction method.Large-section tunnels often have complicated excavation steps due to the large cross-sectional area,and multiple complex steps such as block excavation-supporting form a mechanical repeated loading and unloading process on the surrounding rock mass.Affect the stability of surrounding rock and lining structure.At the same time,due to the large span of the large-section tunnel and even the super-large-section tunnel,the surrounding rock will undergo continuous deformation during the construction process and the later stage of support.Therefore,this paper relies on the special construction method of the super-large section of the Liantang tunnel,based on the time-varying theory of surrounding rock The plastic constitutive model numerically simulates the whole process of the tunnel,comparatively studies the deformation evolution law of surrounding rock during dynamic excavation of the tunnel and the stress distribution law after lining support,and optimizes the analysis of the expansion method of the joint and the step size of the small clearance step,And confirm the reliability with the measurement results,The main research contents and conclusions are as follows:(1)The survey summarizes the construction status of large-section tunnels at home and abroad,the law of deformation of surrounding rock and lining stress over time during tunnel engineering excavation,and also summarizes the optimization of construction of some large-section tunnels.(2)Combined with the engineering overview of the K1880～K1901 mileage 21 m section of the Liantang tunnel super-large section,the double-wall guide pit and the special process dynamic excavation of the tunnel’s super-section are numerically simulated.The time-varying theory is introduced in the excavation simulation The tunnel excavation was simulated with the viscoelastic-plastic coupled constitutive model of ANSYS software,and the horizontal and vertical deformation of the surrounding rock during the excavation of the palm face was comprehensively analyzed.The law of stress redistribution with time after the initial lining was completed Through the numerical simulation results of two methods and the monitoring and measurement of the surrounding rock deformation data,the advantages and disadvantages of the dynamic construction of the super-large cross-section tunnel special construction method are mutually confirmed.(3)The dynamic simulation analysis of the expansion excavation of K1901～K1915mileage gradual change section.Comprehensive deformation of surrounding rock and stress of anchor bolts found that the use of steel truss as a temporary support in the expansion process has a good effect on controlling the deformation of surrounding rock.At the same time,the optimization analysis of the expansion footage is made and the result of 2.5m expansion footage is the best.(4)The numerical simulation of the double-hole excavation in the small clearance section was carried out by the step method.It was found that the construction of the later excavation tunnel caused greater disturbance to the first excavation tunnel,resulting in a higher stress in the second lining of the first excavation tunnel and a horizontal deformation of the middle rock Excavate the side of the hole.Comprehensive analysis of the surrounding rock deformation and lining stress distribution rules shows that after excavating the tunnel,the 4m step is the best.(5)For the construction method of the super-large section and the joint,the construction sequence and excavation footage of each guide pit block of the palm face are refined,and improvement measures are proposed for the excavation process,which are improved from the perspective of safety measures,quality control,environmental protection measures,etc.The construction method of the super-large section and the joint at the bifurcation of the sandstone tunnel is given. |
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