Simulation Analysis Of Formation And Evolution For Longitudinal Cracks In Permaforst Roadbed Along The Qinghai-tibet Railway

There are many longitudinal cracks that appear on the slope and top surface of permafrost roadbed in Qinghai-Tibet Railway during the period of construction and operation due to the cryogenic course of frozen soil, which have severity negative impact on the permafrost roadbed. The current research of longitudinal crack mainly focused on the formation and evolution from the perspective of qualitative or indirect analysis based on field monitoring and traditional FEM. In fact, the traditional FEM neither accurately simulate nor really reflect crack as the crack is discontinuous problem. Therefore, this dissertation has firstly simulated formation and evolution of longitudinal cracks in permafrost roadbed along Qinghai-Tibet Railway via XFEM. The research results not only provide theoretical foundation for the prevention and management countermeasures, but also have important implications for other proposed road engineering in permafrost region.First of all, this dissertation has quantitatively analysed the unsynchronized phenomenon during the melting and freezing processe after the construction according to the principle of thermodynamics.Secondly, this paper has simulated formation and evolution of longitudinal cracks under the effect degree in sun radiation based on the maximum normal stress damage criterion through XFEM after establishing the thermal-mechanical sequentially coupled model. The results have revealed that the tension stress zone on subgrade surface appeared primarily in thawing period, which effected by the thermal radiation conditions, except for slope toe impacted by concentration of stress; and the crack on the the shoulder of sunny-slope have underwent four stages; and compared with the crack on the the shoulder of sunny-slope whose depth is about 4.5m, the depth of crack on the the shoulder of sunny-slope is lower; and the shape of crack is vertical in general,and it appear fluctuations in part, which are consistent with engineering practice.Finally, on the basis of the above analysis, this dissertation has analysed the three major factors for the formation and evolution of longitudinal cracks:filling properties, thermal radiation conditions, load. The results indicate that improving tensile strength of filling is effective way to retard the development of cracks; and lowering degree of asymmetry of temperature fields plays a limited role in controlling the development of crack; and the load has obvious effect on the longitudinal crack; and the expansion depth and open degree of the longitudinal crack increase with the load.