Temperature Effect And Size Effect On Crack Evolutionof Guilin Red Clay

Red clay is a kind of special soil which is easy to shrink and lose water.It is easy to be affected by temperature and size.Southern China is in a humid and hot subtropical monsoon climate,and the variation of temperature has a great impact on the engineering properties of soil.Red clay distributes in most provinces of the south.It is urgent to study the influence of ambient temperature and size effect on the crack evolution of red clay.Taking Lingui red clay in Guilin,Guangxi as the research object,combined with laboratory tests and theoretical analysis,the evolution law of cracks during the drying process of red clay at different temperatures and sizes was studied.Fissure image processing was carried out by PCAS software,and the characteristic parameters of fissure development of Guilin red clay were quantitatively analyzed,and combined with structure of red clay mineral crystal layer and change of double electric layer thickness are explained.The main contents are as follows:(1)Self-developed HD automatic camera and weighing device,the fracture development of Guilin red clay was photographed automatically,The obtained fissure images were binarized by PCAS software,image miscellaneous point removal,fissure repair,block recognition and fissure recognition,and the characteristic parameters of fissures were quantitatively analyzed.(2)The evaporation process of red clay is mainly divided into three stages: constant rate stage,variable deceleration rate stage and residual stabilization stage.With the increase of temperature,the evaporation rate of soil sample increases,and the time for soil moisture content to reach residual stabilization stage becomes significantly shorter.The three stages of water evaporation increase with the size of red clay.(3)Crack evolution at different temperatures which can be divided into three stages: the initial stage of micro-fracture generation,the stage of fracture propagation and the stage of fracture stabilization.The temperature effect of the fissure evolution of Guilin red clay is obvious.With the increase of temperature,the three stages of the fissure evolution of Guilin red clay become shorter,the critical moisture content of initial cracking decreases,the growth rate of fissure area increases,with the increase of temperature,the number of final fissure blocks decreases and the final fissure rate increases(4)The fracture evolution of guilin red clay also has a certain size effect.At the same temperature and the initial soil sample height,the surface crack rate of red clay samples with different diameters increased with the increase of sample size.At the same temperature,the growth rate of the crack rate of different sizes is basically the same.The larger the sample size,the longer the time for the red clay to reach the crack stability stage,the smaller the boundary effect of the crack,the more the number of blocks in the crack,and the larger the WSC of the critical moisture content of the initial crack.(5)The XRD test results show that the maximum temperature of 60? does not change the intergranual spacing of the soil.Based on the principle of double layer,the suitable equation of diffusion double layer is deduced.As the temperature increases,the Zeta potential increases and the thickness of double layer increases.The variation of gas-liquid interfacial tension(surface tension)between soil particles is an important cause of shrinkage and cracking of red clay.In the process of shrinkage and cracking of red clay,the interior of red clay undergoes three states: saturated state,unsaturated state(water-gas-particle interface)and dry state.Based on the data of initial cracking moisture content of red clay at different temperatures,the corresponding empirical formulas are fitted.