| Red clay and expansive soil are two typical types of expansive soil in Guangxi.Among them,red clay has the characteristics of high liquid-plastic limit,strong hydrophilicity and severe shrinkage deformation.Expansive soil has the characteristics of water absorption,swelling softening,water loss,shrinkage and dry cracking,which are closely related to the shape and content of bound water.By studying the testing methods of bound water in soil and the types and contents of bound water in the above soil samples,it is helpful to solve the important influence of the special engineering performance on geological hazards and slope stability.In this paper,Guilin red clay,Liuzhou red clay and Nanning expansive soil in Guangxi are taken as the research objects.The testing methods of bound water in soil,the influencing factors of bound water content and the effects of bound water on the macroscopic properties of soil are studied.The main research results are as follows:1.Aiming at the problem of accuracy and temperature influence of volumetric bottle,a correction method of volumetric bottle measurement combined with water is proposed,which can greatly improve the accuracy of experiment.When the content of strongly bound water in soil is very low,volumetric bottle method is not recommended,because the human error and mechanical error will have a greater impact on the test results.2.Isothermal adsorption tests were carried out on Guilin red clay,Liuzhou red clay and Nanning expansive soil,and two inflection points RH=0.066 and 0.908 on the isothermal adsorption curve were determined according to the results of volumetric flask method,which were the boundaries of strong-bound water and weak-bound water,weak-bound water and free water,respectively.It was found that the density of hydrated soil changed with relative humidity and isothermal adsorption curve.The law is the same.The curve changes steadily in the range of RH=0.066~0.908 and steepens immediately after RH=0.908,which verifies the correctness of the determination of bound water by isothermal adsorption line.3.Reasonable test conditions for determining bound water in soil by thermal analysis method are determined through experimental analysis.The test results of soil samples show that both electrolyte and high temperature treatment at 250 have a great influence on the characteristic temperature of DSC curve partition;high temperature treatment at 250 can reduce the hydrogen bond bonding strength of soil samples and the amount of strongly bound water adsorption.4.By comparing and analyzing three methods of combined water testing,i.e.volumetric bottle method,isothermal adsorption method and thermal analysis method,it is found that volumetric bottle method is not accurate enough to distinguish strong and weak combined water;isothermal adsorption method is time-consuming,low humidity and maximum humidity are difficult to control,and it is possible that the characteristic boundary points of partial humidity are difficult to distinguish accurately;thermal analysis method is the most accurate and economical of the three methods.The optimum method of soil sample pretreatment without high temperature is proposed.5.Through the analysis of the bound water content of Guilin red clay,Liuzhou red clay and Nanning expansive soil,it is found that the colloidal group in the granular group has the greatest influence on the bound water content;mineral composition is the decisive factor affecting the bound water content;liquid-plastic limit is the macroscopic appearance of the bound water content,and its plastic and liquid limits correspond with the bound water content of strong and weak respectively;the bound water content is the influencing factor of the soil.Shear strength is an important internal factor. |
