| CZ railway is the first high-speed railway connecting Tibet Autonomous Region and Sichuan Province.The railway runs east-west and crosses mountains from Sichuan Basin,which is of epoch-making significance.Among them,the construction of Lhasa-Nyingchi section is particularly critical.The construction of Lhasa-Nyingchi railway is of great significance to Tibet.The connection between Lhasa-Nyingchi railway and Qinghai Tibet railway connects Nyingchi with the mainland of China,laying a solid foundation for the docking technology and construction preparation of other sections of Lhasa-Nyingchi railway,Yunnan Tibet railway and Gansu Tibet Railway in the future.Most of the strata crossed by Zhongshan Ridge Tunnel of Lalin railway have complex and diverse geological conditions,especially the overall strength of surrounding rock in weak strata is low,which is easy to cause the problem of surrounding rock instability and deformation.The process of tunnel excavation is affected by construction conditions,geological conditions,water temperature environment,tunnel section,buried depth and other factors,among which the selection of economic and applicable construction methods is particularly important.If the tunnel excavation method is not selected properly,it will not only cause the instability and deformation of surrounding rock and the collapse of tunnel face,affect the construction safety,but also affect the construction speed and increase the cost of tunnel.Taking the Langzhen No.2 soft rock tunnel in the Lhasa Nyingchi section of the national key Lhasa-Linzhi railway as the research object,through data collection and ANSYS finite element numerical simulation,this paper analyzes the stress and deformation characteristics of the surrounding rock and initial support of the tunnel whose excavation section passes through phyllite stratum,selects different excavation methods for numerical simulation calculation,and compares and selects the excavation method suitable for this soft rock tunnel,It provides some reference for the design and construction of similar tunnels.The specific work of the above research is reflected in the following points:1.Analyze the site monitoring data of Langzhen No.2 soft rock tunnel,and study the size,growth mode and distribution of internal forces in soft surrounding rock tunnel bearing surrounding rock pressure and initial lining.The influence of tunnel cross section position on surrounding rock deformation is analyzed,the deformation position of tunnel dangerous section is predicted,and the tunnel cross section monitoring point in the numerical simulation process is determined.2.Taking langzhen No.2 soft rock tunnel as the prototype,using ANSYS finite element analysis software,this paper studies the general law of the stress characteristics of the surrounding rock and lining structure of xialangzhen No.2 tunnel excavated by the upper and lower steps,compares it with the field measured values,and analyzes the similarities and differences between the stress modes of the surrounding rock and lining structure of the upper and lower steps method and the measured results.3.The numerical calculation and analysis method is used to study the deformation and failure law of surrounding rock,the stress state of surrounding rock and the stress characteristics of support structure under four tunnel excavation methods.The comparative analysis method is used to compare the excavation and support process of upper and lower steps method,upper and lower steps reserved core soil method,CD method and CRD method,so as to provide corresponding reference for the design and construction of other projects in the future. |
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