Experimental Studies On Red Clay Soil In Wuhan Under Freeze-thaw Cycles Condition

Red clay soil is widely distributed in China,especially in Yunnan Guizhou Plateau and Hubei Province.As a special soil,red soil clay is the carrier of many projects,and the "disaster" brought by its soil properties will also appear frequently in the project construction.Under the influence of extreme weather,abnormal cold weather often occurs in Wuhan.The outdoor temperature will be as low as below zero.The shallow soil in nature will freeze.When the temperature is raised,the soil will melt again.This repeated freezing and thawing will have a huge impact on the physical and mechanical properties of red clay.At present,there is little research on the physical and mechanical properties of red clay under the freeze-thaw cycle,so this paper takes the remolded red clay in Wuhan as the research object,and studies the effect of freeze-thaw cycle on the mechanical properties of red clay by means of laboratory test.The specific work and research results are as follows:(1)In this paper,a large number of geotechnical tests and X-ray diffraction tests are carried out on the air dried and crushed red clay,and the geotechnical parameters such as density,moisture content and material composition of the test soil samples are measured.(2)Based on the closed freeze-thaw cycle test without water supply,the frost heaving rate and water redistribution of the sample after freeze-thaw were studied.The results show that the frost heave rate decreases with the increase of freeze-thaw cycles,and the decrease range is smaller and smaller,and the frost heave rate finally tends to be stable.After freezing and thawing,the water distribution in the soil is not uniform,showing high water content at both ends and low water content in the middle.With the increase of freezethaw cycles,the moisture content at both ends of the sample is higher,the moisture content in the middle of the sample is lower and lower,and the range of change is gradually smaller.(3)Based on the direct shear test,the shear strength of remolded red clay with different moisture content was measured after 0-5 freeze-thaw cycles.It was found that the cohesive force of soil decreased with the increase of moisture content and the number of freeze-thaw cycles,which was approximately exponential function relationship.The cohesive force decreased significantly after the first two freeze-thaw cycles,and decreased slightly after the last several freeze-thaw cycles.The internal friction angle decreases with the increase of moisture content,and fluctuates up and down with the increase of freezethaw cycles.(4)A triaxial test was carried out on remolded red clay with 25% water content after 0 ? 5 cycles of freeze-thaw,and the test results were compared with the direct shear test under the corresponding water content.It is found that different test methods will not change the basic trend of shear strength index changing with the increase of freeze-thaw cycles,but the cohesion of direct shear test is greater than that of triaxial test,and with the increase of freeze-thaw cycles,the difference between the cohesion is smaller and smaller.The internal friction angle of the direct shear test and the triaxial test have mutual magnitude.The fluctuation range of the former is larger than that of the latter.(5)Combined with the stress-strain curve of triaxial test and Duncan Chang model,the variation of initial tangent modulus and secant modulus with the number of freeze-thaw cycles and confining pressure is obtained.The initial tangent modulus decreases with the increase of freeze-thaw cycles,and finally tends to be stable,and increases with the increase of confining pressure.Secant modulus decreases with the increase of freeze-thaw cycles and increases with the increase of confining pressure.When freeze-thaw cycles and confining pressure are fixed,secant modulus decreases with the increase of axial strain,and finally tends to level.(6)Based on the theory of damage mechanics,Weibull probability distribution,Mises yield criterion and secant modulus,the damage constitutive model of red clay under triaxial loading after freezing and thawing for a certain number of times is established.