Study On The Changes In Physical And Mechanical Properties Of Silty Clay After High Temperature Heating

Thermal desorption treatment technology is an effective means to treat organic contaminated sites,among which ectopic thermal desorption technology is a technical method to remove contaminated soil,use direct or indirect heating method,and heat contaminated soil to vaporize pollutants by controlling temperature and heating time,so as to achieve the separation and removal of target pollutants from soil particles.The physical and mechanical properties of soil change after thermal desorption heating.In order to explore the evolution law of soil physical and mechanical properties after different heating temperatures and different heating times,this paper takes silty clay in Changchun area and Funing area with different organic matter content as the research object,and according to the low temperature ectopic thermal desorption heating environment,The change of physical and mechanical properties of soil after heating at100℃-300℃for different time was studied,so as to provide theoretical support for minimizing the influence on engineering properties of soil under the premise of ensuring the heating effect of thermal desorption.In this paper,the experimental research method was adopted.After screening the soil samples from Changchun and Funing areas,the soil samples with the same density and moisture content were prepared by means of the percussion sample method.152effective samples of each soil were made,and the samples were divided into groups and heated at a constant temperature of 100℃,200℃and 300℃in high temperature oven.The constant temperature heating time was 3h,6h,12h,24h,48h,96h.After different heating time,8 soil samples were taken for basic physical property parameter experiment,direct shear experiment,unconfined compression experiment and consolidation test.8 samples were taken to test the basic characteristics of the soil before heating.Finally,the two kinds of soil were heated at a maximum heating temperature of 300℃for 96h,and the microstructure and chemical composition analysis experiments（SEM and XRF）were conducted before and after heating to analyze the influence of high temperature heating on their structure and material composition.The details are as follows:（1）Through the physical property experiment,the mass loss rate,particle size composition and liquid limit and plastic limit water content of the soil under different heating conditions were tested.The results show that the mass loss of soil will be caused by heating.The mass of soil sample decreases with the increase of heating time.The higher the temperature is,the shorter the time it takes to stabilize the mass.Due to the agglomeration of clay particles to powder particles at high temperature,the percentage of sand particles does not change much with the increase of heating temperature,the percentage of powder particles increases,and the proportion of clay particles decreases.However,in the particle size range of 0.002mm<d<0.005mm,the percentage content of Funing soil increases,and the percentage content of Changchun soil decreases.The liquid limit and plastic limit of soil decrease with the increase of heating time and heating temperature.The variation of plasticity index of Funing soil with temperature is small,while that of Changchun soil is large.（2）The cohesive force,internal friction Angle,unconfined compressive strength and compression coefficient of soil under different heating conditions were tested through mechanical property experiments.It is found that the silty clay soil cohesion decreases with the increase of time temperature,the internal friction Angle increases with the increase of time temperature,and the unconfined compressive strength decreases with the increase of heating time and heating temperature.The compression coefficient decreases with the increase of heating time and heating temperature,while the compression modulus increases with the increase of heating time and heating temperature.（3）Through SEM and XRF experiments,the microstructure and chemical composition of the soil samples heated at 300℃for 96h were analyzed before and after heating.The experimental data show that with the increase of heating temperature,the micropores between units and particles decrease and the macropores increase.The contact mode between particles is changed,and some particles aggregate to form lamellar or granular aggregates or lamellar or plate-like aggregates.The formation of new chemical and mineral components in soil samples,as well as the eutectosis between compounds,cause the chemical composition of silty clay to change.It shows that the content of Si O₂ increases with the increase of heating time,while the content of Fe₂O₃ and Al₂O₃ increases first and then decreases with the increase of heating time.