Study On Mechanical Properties And Microstructure Of Silty Clay Roadbed In Seasonnal Frozen Zone

Zhangjiakou dam area is located in the northern part of Zhangjiakou,with an average elevation of 1400 meters,due to the geographical location of special perennial temperature is lower.With our efforts to increase the development of renewable energy,more and more transportation facilities need to be built in this area,with highways occupying a certain proportion.According to our previous experience in the construction of seasonal frozen area in our country,many problems appeared in the area due to frost damage.For example,roadbed frost heaving caused uneven road surface,after the spring thaw subsidence caused by subsidence,subgrade migration within the water lead to uneven settlement,after repeated freeze-thaw cycles,the mechanical properties of subgrade led to lower bearing capacity.In order to make the construction of frozen zone work smoothly in future,this paper studies and summarizes the mechanical properties and microstructure changes of subgrade soil under the action of freeze-thaw cycles.The main line of this paper is to study the static characteristics and microstructural changes of highway subgrade fillings after freeze-thaw cycles in Zhangjiakou area.In this paper,a high-speed subgrade fill in Zhangjiakou is taken as research object.Through indoor static triaxial test,freeze-thaw test,electron microscopy test,the test results were significantly analyzed to calculate the mechanical properties of subgrade soil greatest impact on the combination of factors,the combination of the specimen after freeze-thaw microstructure changes observed electron microscopy,according to changes in microstructure to explain changes in macro-mechanical parameters the reason.According to the main research article is divided into the following points:(1)Laboratory physical properties of the test,including: particle analysis test,the limit moisture content test,compaction test.According to the test results,the soil is classified according to the project,and the compaction degree and moisture content design of the sample are prepared according to the code for design of highway subgrade and the monitoring data in the actual project.(2)Specimens with water content and compaction set for the freeze-thaw cycle test were designed to reach the designed number of freeze-thaw cycles,then subjected to unconfined and undrained static triaxial compression test.Four factors(freeze-thaw Cycle number,degree of compaction,moisture content,freezing negative temperature)changes in the specimen deviation value,internal friction angle and cohesion parameters of change,the test results were analyzed and significant analysis of the factors that determine the test results The degree of influence,to determine the most influential combination of test parameters.(3)Electron microscopy was carried out on the test pieces made of the combinations with the greatest influence on the test results in the above(2),and the average perimeter of the sample pores,the porosity,the average particle diameter of the soil skeleton particles,The average area and other statistical results,the changes in the microstructure to explain changes in macro-parameters.