Train-induced Dynamic Response And Permanent Deformation Of Embankment In Permafrost Region Along Qinghai-tibet Railway

With the completion of the Qinghai-Tibet Railway, several damages induced bythe traffic loads have been occurring to the permafrost subgrade, and the safe-operationdemand and speed-increasing scheme of the railway will therefore be affected seriously.In view of this, considering the background of the long term operating performance ofthe ice-rich permafrost sloped-subgrade along the QTR subjected to traffic loads andannually changing climate, the present thesis attempts to present relevant fundamentalresearches on such key issues as the dynamic performance of frozen and thawing soil,the vibration response of the subgrade, and the permanent deformation induced bytraffic loads. Laboratory tests, theoretical analysis and numerical simulation are takenas the main technological measures to perform the investigation. The original work ispresented in detail as follows.(1) Based on the Cyclic-dynamic triaxial tests, the dynamic behavior of frozen siltclay of the QTR subgrade subjected to the variation of dynamic stresses, of externalenvironmental conditions, and of physical features of soil is examined, and emphasis isalso given to the evolution of elastic deformation and cumulative plastic deformation offrozen silt clay induced by vibration loads. Specifically, a resilientmodulus-based-model is established on the basis of the obtained data, and the relationmodel between cumulative deformation and such parameters as dynamic stresses,number of vibration, and frozen temperatures is proposed as well, taking criticaldynamic stress as the normalization factor.(2) With the above-mentioned tests performed, a further research of the influenceof freezing-thawing cycles, thawing temperature, amplitude of dynamic stresses on themechanic features of the frozen silt clay of the QTR sloped-subgrade is carried out, inview of the characteristics of seasonally frozen soil and traffic loads. Special attention ispaid to the development of elastic and cumulative deformation of silt clay subjected toboth freezing-thawing cycles and traffic loads, and another relationship model ofresilient modulus, cumulative plastic deformation and freezing-thawing cycles isobtained, which together with the model mentioned above can provide theoreticalfoundation for the later calculation of permanent deformation of the QTR sloped-subgrade.(3) A three dimensional finite element-infinite element model on the vibrationresponse of the QTR sloped-subgrade is established. Our team’s train-track-subgradevibration program is adopted to simulate the traffic loads, that is, the calculatedtrack-sleeper forces, and the obtained forces are then imposed on the three-dimensionalsloped-subgrade model so that the temperature field can be coupled with the stress field.The effects of primary parameters such as travelling velocity, train axle, and subgradeon the vibration response of sloped-subgrade are compared based on the simulationresults, and the sensitivity analysis of parameters is performed trough intersectionexperiment design principle, by which the mechanism on the dynamic characteristics ofthe sloped-subgrade of warm permafrost region is further clarified.(4) On the basis of the established cumulative-permanent-strain model of frozenand thawed silt clay subjected to cyclic traffic loads, the Drucker-Prager-basedvisco-elastic plasticity sub-program CREEP is developed. Taking the well-obtaineddynamic stresses of subgrade as the initial state variable, the numerical model on thepermanent deformation of the QTR subgrade considering both the effects of groundpressures and dynamic stresses is built, based on which the permanent deformation ofsloped-subgrade induced by traffic loads is predicted, and the influence of train axle,traveling velocity, and vibration numbers on the permanent deformation is investigated.