| The Yangtze River Delta region has a solid economic foundation and a complete urban system,which is shouldering the national mission of constructing a new development pattern and leading the high-quality economic development in the new era.The corresponding urban underground rail transit construction is also in the booming stage,but the special geological conditions in the Yangtze River Delta region is worth considering,Due to the strong consolidation and creep of soil and the variation of underground water level leakage,the operation safety of metro tunnels in the Yangtze River Delta region is facing more and more risks and challenges.Based on the engineering of Nanjing subway tunnel as the background,using the field measurement data,determine the creep is a key factor to the subsidence of soil,soil and soft soil layer is studied from the perspective of the deformation of tunnel under long-term problems,reveals the stratum deformation backing the mechanical response of the tunnel,finally focuses on the tunnel horizontal convergence and segment disease characteristics such as open,The relationship between segment opening disease and lateral convergence is established,and the safety evaluation method of shield segment is put forward,which provides guidance and theoretical basis for prevention and treatment of circumferential segment opening and water leakage and other diseases and for ensuring tunnel operation safety.In this paper,the relevant mechanism of segment opening disease of shield tunnel operating in soft soil area is studied,which includes the following aspects:(1)Based on the monitoring data of Nanjing metro in operation and its stratum mechanical properties,the long-term settlement law of the stratum in this area and its influence on the tunnel structure are analyzed,and the influencing factors of long-term settlement of the tunnel structure in operation are summarized.SPSS software is used to analyze the influence degree of timeliness,train load,accumulated settlement,underground water level and other factors on the existing tunnel structure.It is pointed out that creep is the most critical factor affecting the long-term settlement of existing tunnels in soft soil area of floodplain,which lays a foundation for the subsequent research.(2)Modification of Burgers constitutive model.Taking shield tunnel in creep soil in Nanjing area as the research object,the existing Burgers model was modified to make it more suitable for the characteristics of soft soil layer in flood plain,considering that creep stratum has the characteristics of both hardening and hysteresis,which can pave the way for subsequent theoretical derivation and numerical simulation.(3)Theoretical and numerical methods are used to analyze the mechanical response of tunnel structure in creep stratum.Based on the theory of viscoelastic mechanics,the viscoelastic solution of mechanical response between stratum and shield tunnel in soft soil area is derived.By introducing the revised Burgers viscoelastic constitutive model and developing the ABAQUS subprogram,a numerical calculation method suitable for the characteristics of soft soil in floodplain was proposed.The viscoelastic analysis of the internal force,transverse and longitudinal convergence and joint opening of shield tunnel segment in soft soil area was carried out and compared with the theoretical results.The validity and accuracy of the model are verified.(4)The safety evaluation method of shield tunnel segment is proposed and verified in practical engineering.Firstly,the possible diseases of common segment joints are identified.Then,the relationship between lateral convergent deformation and bolt yield,water leakage and other diseases of shield tunnel is established by numerical method.Combined with the specification and material strength requirements,the segment safety critical value is proposed and its safety level is determined,thus providing theoretical guidance for the prevention and control of shield segment disease. |
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