Study On The Variation Law Of Reinforcement Prestress In Railway Prestressed Subgrade

Prestressed subgrade is a new type of roadbed structure.Its main function is to constrain the embankment slope and increase the horizontal confining pressure by applying prestressed steel bars,at the same time improve and enhance the long-term static and dynamic performance of the roadbed and the local and overall stability of the slope.Our research group has carried out a series of researches on the reinforcement performance,mechanism and design theory of prestressed subgrade and achieved many research results.As the core element of this new subgrade structure,the level of prestress is related to the long-term stability of the project.In this regard,this thesis studies the variation law of prestress in the subgrade,and the main work is as follows:(1)By analyzing the working mechanism of the prestressed subgrade structure and its engineering application characteristics,the change of the steel prestress is divided into two characteristics: prestress loss and fluctuation change,and the main influencing factors of the loss and change of the steel prestress in the prestressed embankment are summarized.(2)Construct a 1:5 large-scale prestressed subgrade model test system.Through the experimental research on the instantaneous loss,short-term loss and long-term loss of steel prestressing in the subgrade,the loss rule of the steel prestressing in the prestressed subgrade is verified,and the steel reinforcement is given,and gives the relevant suggestions for the compensation of steel prestress loss.(3)Based on the theory of elasticity,a calculation method for the additional stress on the horizontal path behind the center point of the contact surface between the prestressed subgrade side pressure plate and the embankment slope is proposed.The analysis shows that the horizontal additional stress on the characteristic path exhibits a good exponential function decay relationship with the increase of the distance from the center point of the plate-soil contact surface.Based on the above attenuation law and the creep behavior of the embankment soil,the calculation formula of the creep deformation of the embankment soil is deduced,and the loss model and calculation method of the embankment prestress are established by combining it with the coordination of the retraction deformation of the prestressed steel bar,and the validity of the model is verified based on numerical simulation.(4)Based on the test model of the prestressed subgrade after the steel prestress is stabilized,the variation law of the steel bar prestress under the cyclic action of four typical train loads is studied.At the same time,the numerical model of the prestressed subgrade was established by using large-scale finite element software,the response characteristics of the prestressed steel bars in the embankment under the dynamic load of the train were analyzed,and the transient response law and the spatial distribution characteristics of the steel bar prestressed in the embankment were proved.(5)Based on the prestressed subgrade test model after the steel prestress is stabilized,the effect of temperature on the steel prestress level in the embankment is carried out,and the variation law of the prestress level with temperature is verified.