Experimental Study On Structural Parameters Of Guiyang Red Clay Based On Shrinkage Characteristics

Red clay formed by weathering of carbonate rocks is widely distributed in Guizhou Province,it has poor physical properties such as high water content,high porosity,and high limit water content,but also has good mechanical properties.As a special soil,red clay is often involved in engineering construction in Guizhou.This article takes the red clay around Hongfeng Lake in Qingzhen City,Guiyang City as the research object.,through geotechnical test,shrinkage test,unconfined compressive strength test and a series of micro-tests,the influence of shrinkage characteristics of Guiyang red clay on its soil structure is discussed,which has certain theoretical and practical significance.The main research contents of this paper are obtained as follows:(1)The moisture content test,specific gravity test,density test,limit moisture test,compaction test,consolidation test,swelling and shrinkage test were performed on the red clay to determine the shrinkage index,such as physical and mechanical indexes,linear shrinkage,and shrinkage coefficient and so on.Based on the test results,the shrinkage process of Guiyang red clay was analyzed,and the causes of abnormal physical and mechanical indexes of Guiyang red clay were discussed in detail.(2)Conducting shrinkage tests on Guiyang red clay with different initial states,obtain the influence of initial state on shrinkage characteristics of red clay.Soil shrinkage undergoes normal shrinkage,residual shrinkage,and zero shrinkage,analyze the change of soil structure at various shrinkage stages,and clarify the shrinkage mechanism of red clay shrinkage.The shrinkage geometric factor r_s was used to evaluate the anisotropy of the red clay,and found the influence of initial moisture content and dry density on the shrinkage anisotropy of red clay.The G&C model was improved by combining different initial states of the soil.The improved model can completely reflect the change of the porosity ratio during the shrinkage of red clay under different initial states.(3)The unconfined compressive strength tests were conducted,in order to study the macromechanical characteristics of the original,remodeled,and shrinkage-stabilized soil samples of Guiyang red clay,compared the stress-strain curves and failure modes of the samples under different initial conditions,analyze the variation of unconfined compressive strength with moisture content and dry density.Based on the idea of comprehensive structural potential,the soil structure is changed by two methods of disturbance and shrinkage.A shrinkage structure parameter Q_S that reflects the soil structure is proposed,Q_S has a quadratic polynomial function relationship with the comprehensive structural state and shrinkage index.the shrinkage index of the red clay in any initial state can be solved through the shrinkage structure parameters.(4)In order to study the microstructure characteristics of Guiyang red clay,a series of micro-tests were performed on the samples.Through the X-ray diffraction test,analyzing the material composition of red clay,Compared with general clay,the content of montmorillonite is higher,it has stronger swelling and shrinking characteristics.Scanning electron microscopy was used to analyze the microstructure and morphology of the samples,and we can find the characteristics of contact and connection between the red clay particles and pores,it is mainly a flocculated structure and a honeycomb structure,which constitute the pores between the particles or aggregates and the pores within the particles.Through the mercury intrusion test,the changes in the pore characteristics of red clay during shrinkage are given.The shrinkage of red clay mainly occurs in the middle and large pores.The moisture in this part of the pores dissipates,leading to a decrease in the interval between the particles or aggregates.The volume is reduced,and the micropores and pinholes hardly shrink.(5)Considering the shrinkage characteristics of Guiyang red clay,the wall cracks in the study area were investigated and analyzed.It was found that the wall cracks were caused by the uneven settlement of the houses caused by the shrinkage of red clay,and suggestions were made to reduce the occurrence of similar phenomena.In this paper,through laboratory tests,micro experiments and engineering applications,the evolution of physical properties,soil structure and mechanical parameters during the shrinkage of red clay in different initial states is described,and the water loss shrinkage characteristics of Guiyang high-liquid red clay are revealed in essence And the harm brought by it can provide a certain reference for preventing the uneven settlement of projects such as exposed building foundations and red clay embankments.