| Subgrade is the main bearing structure of the railway.Its quality is directly related to the safety and comfort of railway operations during the period of service.Due to the subgrade constructed is exposed to the harsh natural environment,the engineering properties of the soil,including the elastic modulus,are deeply weakened by the influence of water infiltration,such as rainfall,immersion and so on,which would seriously affects the dynamic response of the subgrade under the train load.Two methods,including indoor unit model test and nonlinear dynamic finite element numerical simulation,were carried out comprehensively to indicate the effect of water infiltration on the dynamic response of ballasted railway subgrade induced by train load.The main work as follows:(1)A simulated rainfall device that can be used to control the rain intensity was developed.An indoor unit model test of track bed-subgrade structure was carried out to analyse the water infiltration mode of ballasted railway subgrade under two controlled conditions of rainfall infiltration and subgrade soaking,the time-space variation law of subgrade soil water content at different depths during water infiltration was studied,and the state of moisture content of the soil in the subgrade after water infiltration was revealed.(2)By using the large hydraulic servo loading system,200,000 cyclic loads were applied to the ballast-subgrade structural unit model under the three conditions of optimal moisture content,rainfall infiltration under the set rain intensity,and roadbed immersion for 10 days.The development history of dynamic response of soil dynamic stress,excess pore pressure,elastic deformation and cumulative deformation of ballasted railway subgrade under three control conditions was compared.The effect of different water infiltration on the dynamic response and service performance of subgrade structure was discussed.(3)The fundamentional theories of the finite element numerical simulation in dealing with the dynamic problems in geotechnical engineering were summarized.Among them,the basic balance equation,load handling,the establishment of mass matrix and damping matrix,and the solution method of motion equation were described systematically.(4)A finite element analysis program for geotechnical engineering nonlinear dynamic problems which based on the Newmark implicit integration method was coded with FORTRAN language.The framework for the composition of the source code,the internal calculation process for each analysis module,and a description of the input data card were proposed.After comparing with the calculation results obtained by the dynamic module of PLAXIS program,the relative errors of the two calculation results were analyzed,which verified the accuracy of the coded program by the author.(5)The train load was simulated by an excitation function which composed of static load and three sinusoidal loads.The finite element analysis model of double track railway subgrade was established.The subgrade performance weakening was simulated by the decreasing of elastic modulus of soil layer.Based on the FORTRAN program,the distribution law of vertical dynamic stress,vertical displacement and vertical acceleration after subgrade soil weakening were discussed.The results obtained in this paper have a certain practical significance for enriching the dynamic analysis method of subgrade structure and guiding the optimize of design,construction,operation,and maintenance of railway subgrade... |
PDF Full Text Request