Dynamic Characteristics And Cumulative Deformation Of Coarse-grained Soil Filled Subgrade For High Speed Railway

The rapid development of China’s high-speed railways,with new technologies constantly leading new developments,has become a symbol of China’s leadership in the world.However,with the increase in train running speed and axle weight,the accumulated deformation and settlement of the roadbed has also accelerated,which has put forward more stringent requirements on the roadbed structure.Therefore,it is important to strengthen the research of roadbed and improve the deformation resistance to ensure the safe operation of high-speed railways.In this thesis,the static dynamic characteristics of saturated coarse-grained soil and its cumulative deformation under different fines content conditions are investigated by using indoor triaxial tests.The results can be used as a reference for railway design.The main research content of this thesis contains three aspects.(1)The consolidation undrained triaxial compression test was carried out to consider the development of stress-strain and pore water pressure of coarse-grained soils under different fines content and effective envelope pressure conditions,and to derive the shear strength of three coarse-grained soils.The results show that,with constant fines content,the specimen breaking partial stress gradually increases with the increase of effective envelope pressure;when the effective envelope pressure is the same,with the increase of fines content,the breaking partial stress of the specimen gradually decreases.The superporous water pressure is shown to increase and then decrease to a negative value,the absolute value of superporous water pressure gradually decreases with the increase of the fines content when the effective surrounding pressure is constant.(2)In the dynamic triaxial test,the cumulative deformation of the coarse-grained soil specimens increased with the reduction of the fines content,and the strength of the specimens became lower and lower,the cumulative strain of the specimens decreased with the increase of the surrounding pressure,and increased rapidly with the increase of the dynamic stress amplitude,and reached the peak value rapidly after 1000 times of loading and could gradually stabilise,showing the phenomenon of strain hardening.The modulus of elasticity increases with the increase of fine grain content and increases with the increase of the surrounding pressure,especially in the low dynamic stress conditions,the influence of the surrounding pressure is more significant,with the increase of the dynamic stress amplitude,the modulus of elasticity of the specimen will increase.Dynamic pore pressure development is generally divided into four stages:rapid growth,slow growth,stabilisation and decline.All other test conditions being equal,the modulus of elasticity of the specimen increases with increasing fines content,decreases with increasing effective envelope pressure and increases with increasing dynamic stress amplitude.A prediction model for cumulative plastic deformation considering the stress ratio is proposed based on the data after the first 1000 cycles of loading.(3)Using ABAQUS finite element software,a 3D finite element model of highspeed railway structure was established to study the dynamic response of coarsegrained soil subgrade under high-speed train moving loads.The study found that the dynamic stress on the subgrade is saddle-shaped in the transverse direction and symmetrically distributed about the center of the subgrade,decreasing with depth;vertical displacement and acceleration attenuate in a similar manner with depth as dynamic stress.Under different mechanical characteristic factors,the dynamic response of the subgrade shows different variation patterns.With an increase in fine-grained content,dynamic stress gradually increases while vertical displacement decreases;as the effect of fine-grained content on the subgrade weakens,both decrease with an increase in elastic modulus.Additionally,velocity also has a significant impact on the dynamic response of the subgrade.The dynamic response of the subgrade exhibits significant fluctuations with increasing speed;both dynamic stress and displacement increase with speed but there is a critical velocity.Before reaching critical velocity,both are positively correlated with speed,but once the speed exceeds the critical velocity,they exhibit anomalous behavior and gradually decrease with increasing velocity.