Study On Shrinkage And Cracking Of Road Base Red Clay Soil And Palm Silk Improvement Technology

Red clay soil is a common special soil in the southern region of China,which is very easy to lose water and crack in dry environment,resulting in various engineering geological disasters such as uneven settlement of red clay soil foundation and slope collapse occurring frequently.In-depth study of shrinkage cracking characteristics of red clay soils and elimination of improvement methods to mitigate cracking are of great theoretical significance and engineering value for the solution of engineering problems in red clay areas.This paper takes red clay soil in Shaoyang area of Hunan Province as the research object,by carrying out indoor free shrinkage test,dry shrinkage cracking test and unconfined compressive strength test,combined with digital image correlation technology and fissure extraction technology,to study the shrinkage characteristics of red clay soil,dry shrinkage cracking influencing factors,and the influence law of fissure and strength of palm silk red clay soil,the following main conclusions are obtained:1.Red clay shrinkage is anisotropic,the size and development of shrinkage in different directions are not exactly the same,and there are differences in the strains generated in different parts of the soil.The shrinkage is greatest in the vertical z-direction,followed by the horizontal x-direction,and the smallest in the horizontal y-direction.The shrinkage of the soil body in the horizontal x,y direction is divided into 2 main stages:linear shrinkage stage and shrinkage stabilization stage;the shrinkage in the vertical z direction is divided into 3 stages: soil surface arching stage,linear shrinkage stage and shrinkage stabilization stage.The strain at the edge of the soil sample is larger than the strain at the center of the soil sample,and the tensile strain at the surface of the soil is mainly at the early stage of drying,and the tensile strain will change to compressive strain and increase gradually at the middle and late stage of drying.2.The shrinkage rate of red clay is related to the size of the specimen.An increase in the width of the soil sample from 10 to 50 mm and an increase in the shrinkage in the width direction from 10% to 12.5%;The thickness of the soil sample increased from 10 mm to 50 mm,and the shrinkage in the thickness direction increased from 9.6% to 17.4%.The shrinkage index of red clay should be based on the actual engineering needs using appropriate specimen size.3.The initial water content and specimen thickness to diameter ratio have significant effects on the final fracture morphology,the initial water content increases from 20% to70%,the fracture rate increases by 298.1%,the fracture length increases by 40.5%,and the fracture morphology develops from "fine-dense" to "coarse-sparse " and then to "coarsedense".The thickness to diameter ratio increased from 0.033 to 0.1,the fracture rate increased by 174.5%,the fracture length decreased by 20.8%,and the fracture pattern changed from "fine-dense" to "coarse-sparse".The effects of ambient light intensity and wind speed on the final fissure morphology are not obvious,and the increase of wind speed and light intensity only accelerates the fissure development process.4.The palm silk can better inhibit the fracture development of red clay as well as enhance the compressive strength of red clay.The 4.5‰ dose of 20 mm length of palm silk had the best comprehensive improvement effect on the red clay soil.Compared with the plain red clay soil,the fracture rate,fracture length and fracture width of the improved red clay soil decreased by 53.8%,23.2% and 38.8%,respectively,while the unconfined compressive strength increased by 42.1%.Palm silk improved road base red clay has strong promotion value in highway and railroad and other transportation projects.