Study On Dynamic Characteristics Of Improved Silty Soil Subgrade

There are many rivers in China,and a vast silty alluvial plain is formed along the river basin.Silty sand is used as a roadbed filler for alluvial plains,and its capillary action is strong,which is difficult to meet the requirements of actual engineering.With the development of China's economy and the increasing traffic volume,long-term traffic load damage to the roadbed is also becoming more and more serious,resulting in a series of roadbed diseases.In order to solve the problem of stone shortage in the alluvial plain and damage to the roadbed by traffic load,combined with the actual engineering conditions and the basic properties of silty sand,the silt soil is improved and treated to meet the actual requirements of the project.The engineering properties of the improved soil have changed to varying degrees.Therefore,scientific methods should be used to study the improved soil under different modifiers,different dosages and complex engineering environments to ensure the engineering results.In this paper,the inorganic binder is used to improve the silt soil.Through the indoor test and finite element simulation analysis,the dynamic characteristics of the improved silt soil subgrade are systematically studied.The following research work is mainly carried out:(1)Determine the optimal ratio.The sieving and liquid-plastic limit tests were carried out to determine the physical properties of the silt soil,and the inorganic binder was selected as the modifier to design the orthogonal test.The compaction test was carried out according to the proposed ratio,and the optimum moisture content and maximum dry density of each ratio were obtained.Straight shear and unconfined compressive strength specimens were prepared,and straight shear and unconfined resistance were observed for 7d and 28 d respectively.The compressive strength test obtained the shear strength and the non-lateral compressive strength to determine the optimal ratio.The capillary riser test was carried out according to the determined optimal ratio to determine the water blocking effect after the improvement of the silt soil.(2)Traffic load analysis.The characteristics of the traffic load and the motion law of the mass point in the soil are analyzed.The vehicle model is established by selecting a two-degree-of-freedom quarter vehicle model,and the additional effect of the vehicle on the road surface is obtained.The loading waveforms for the indoor test and the finite element simulation analysis were determined.(3)Analysis of dynamic performance of roadbed filling.Combined with the stress state at different depths of the subgrade,considering the different confining pressure,compaction degree,water content and load frequency,the GDS dynamic triaxial test was carried out on the modified silty soil to study the cumulative axial strain of the modified soil under long-term cyclic loading.The critical dynamic stress,dynamic strength,dynamic modulus and damping ratio of the improved silty sand were analyzed.Under the influence factors of confining pressure,compaction degree,water content and load frequency,the prediction model of the cumulative axial strain of the improved silt is obtained,and the critical dynamic stress,dynamic modulus and strain as a function of the modified silt are obtained.(4)Dynamic response analysis of 3D subgrade simulation.The finite element software was used to establish the 3D subgrade model.The numerical simulation analysis of the 3D subgrade model was carried out under different conditions of driving speed,water content and compaction.The dynamic stress and vertical displacement of the improved silty soil subgrade were studied by different factors.Influence,the law of the dynamic stress of the subgrade with the depth of the subgrade and the distribution law of the vertical displacement under various working conditions are obtained.