Dynamic Response And Load Transfer Behavior Of High-speed Railway’s Geosynthetic-reinforced Pile-supported Embankment In Patchy Permafrost

China’s achievements in high-speed railway construction have been recognized by countries around the world.With the development of ‘go global’ strategy and ‘the Belt and Road Initiative’,permafrost problems are becoming more prominent.The Tieli to Yichun passenger dedicated line,the first high-speed railway in the world that runs through the transition zone between continuous permafrost and seasonal frozen regions,is located on the southern slope of the Lesser Khingan Mountains.The permafrost in this area is extremely unstable with high temperature and shallow water level.Therefore,the stability of high-speed railway subgrade and the interaction mechanism between subgrade structure and permafrost are the key issues.In view of this,this research takes the design and construction of the planned Tieli to Yichun high-speed railway in the patchy permafrost region as the application background,discusses the stability of the pile-supported geogrid-reinforced embankment in the patchy permafrost region,and studies the distribution and transfer law of the static and dynamic stress inside the subgrade under gravity and train load.The research contents,methods and results are as follows.Considering the interaction between geogrid and cushion,the relation between relative displacement and frictional resistance of geogrid and cushion filler was systematically studied using large-scale pull-out test apparatus.In particular,the evolution law between the above relation and geogrid type,cushion filler type,vertical pressure,water content and other factors were obtained.On the basis of the pull-out test results,by introducing the Prandtl solution and the concept of key particle size,a formula for calculating the maximum pull-out force considering water content and different particle size for both biaxial and triaxial geogrid was established.Based on this,a calculation model for the interface between geogrid and cushion was proposed and applied to the finite element simulation.A series of static and cyclic triaxial tests were carried out to investigate the behavior of coarse-grained subgrade filler under the impact of temperature.A model based on the time-hardening approach was proposed to predict the accumulated plastic strain considering the effect of the stress history.And then,an elastoplastic constitutive model has been proposed to describe the behavior of coarse-grained subgrade filler considering the effect of temperature based on the progressive damage theory.The finite element model of pile-supported geogrid-reinforced embankment in the patchy permafrost region was established.According to the field monitoring data of several sites,the simulation results of temperature field,gravity stress field and acceleration were compared with the monitoring results,and the availability of the model was verified.The temperature field in 20 years after construction in patchy permafrost region was calculated.The stability of the embankment was verified by the results of subgrade settlement and the strain of geogrid.This thesis studied the variation of static vertical stress field inside the embankment under different embankment heights,pile spacings,geogrid strength and temperature.The concept of passive earth pressure coefficient was introduced to modify the multi-arching model.And a formula was established to calculate the stress in embankment and geogrid deformation under static load in permafrost region.The acceleration and vertical dynamic stress of subgrade was also studied.It was found that the vertical dynamic stress in subgrade was obviously transmitted in two steps.Based on this,an empirical formula for calculating the additional vertical dynamic stress was proposed.This study explains the evolution law of mechanical properties of the geogridsoil interface under different geogrid types,particle sizes and stress states,and solves the problems of soil pressure and geogrid deformation calculation.And tried to solve the problem in the design of embankments under high-speed train load in patchy permafrost region.The results provide basic research data for further study on the theory,and provide reference for design,operation and maintenance.