Study On Dynamic Characteristics And Numerical Simulation Of Saline Soil Under Temperature Change Condition

Qinghai as the main province for the distribution of saline soils in the west,which has a large area of saline soils,and the engineering mechanical characteristics of saline soils are significantly different.When the saline soil is used as the subgrade base and filler in engineering,engineering diseases of different degrees will occur.it has special circumstances such as repetitiveness and difficulty in treatment.At present,the research focus of saline soils in Qinghai is mainly on the causes,distribution rules,physical and mechanical characteristics and strength characteristics of saline soils,calculation and prediction methods of settlement and settlement of foundations in saline soil areas,and treatment methods for disaster problems.The research on the dynamic characteristics of saline soil under temperature changes is few,especially the failure mechanism of saline soil subgrade under cyclic dynamic load,and no systematic research results have been obtained.The study of the dynamic characteristics of special soils is also an important branch of the development of soil mechanics theory.Therefore,the study of this subject is of great significance for the development and improvement of the dynamic characteristics of saline soils,and can provide a theory for the construction of saline soil areas in Qinghai.This article takes the subgrade saline soil in Chaerhan area of Qinghai as the research object.Based on the GDS dynamic triaxial test system,the cyclic sinusoidal dynamic load under different temperature conditions is applied to obtain the dynamic stress-dynamics of saline soil under different experimental conditions.Strain,dynamic shear modulus,dynamic damping ratio and other parameters that reflect the dynamic characteristics of the soil.Explore the evolution of dynamic stress,strain,and strength of saline soil under dynamic loading,combined with SEM micro-electron scanning test and PFC particle flow.The numerical simulation test summarizes the failure mechanism and development law of saline soil under dynamic load.The following main conclusions were reached:(1)Saline soil in Chaerhan area is a strong chloride salty soil and also contains a small amount of sulfate.Such salty soil is easily soluble in water and has strong hygroscopicity.Very strong cementing ability,due to the presence of a large amount of chloride,the freezing point of the soil will drop significantly.(2)From the dynamic triaxial test in the laboratory,the kinetic data of the saline soil is obtained by analyzing the test data through the hyperbolic model.The increase of the strain amplitude increases,the dynamic shear modulus decreases with the increase of the dynamic shear strain amplitude,and the dynamic damping ratio and the change trend of the dynamic shear modulus are just opposite.The causes of the changes in the maximum dynamic shear modulus,final shear strain amplitude,and maximum damping ratio at positive temperature,negative temperature,moisture content,compaction,and confining pressure were further analyzed.(3)Through the SEM images of the samples before and after the dynamic triaxial test are compared.It is found that this type of saline soil is mainly composed of needle-like rods,prisms,and crystalline salts.These materials are further wrapped and cemented with each other,inlaid and overlap each other.Under different test conditions,the salty soil transformed into a flocculated aggregate with fine structure and fragmentation.The pores,structural unit bodies,microstructures,and roundness of the soil changed significantly,which was closely related to the changes in macromechanics.(4)By numerical simulation of particle flow(PFC),the meso-mechanical parameters of the saline soil numerical simulation are analyzed.From the particle movement displacement,rotation,and particle contact force changes,it is obtained that with the application of cyclic dynamic load,the sample particles gradually move,and the inside of the sample gradually becomes inclined.Cracks and damage,as the deformation gradually increased,multiple groups of shear bands were formed inside the sample later,and the shear bands continued to develop and expand from local to overall.Particle movement and contact fracture between particles in the sample are the inherent causes of macroscopic failure of the soil sample.