Research Of The Method On Determining Atterberg Limits Of Soil By Suction Stress Characteristic Curve

At present in the geotechnical basic test items,the determination methods of the plastic and liquid limit can not be unified,the traditional liquid-plastic limit joint method interfered a lot by human factors.Therefore,due to different soil samples and different operators,the result of the plastic and the liquid limit lies in a wide range.The liquid and the plastic limit,and the liquid and plastic index calculated by it are the main physical parameter in the evaluation of fine-grained soil combined with water content,colloidal clay content and engineering classification in soil mechanics.Therefore,the accurate determination for the liquid and plastic limit of soil is of great significance.In unsaturated soils,the research has become very complex due to the presence of suction.Thereinto the Soil-Water Characteristic Curve(SWCC)is an important feature of relations in the study of unsaturated soil.Suction Stress Characteristic Curve(SSCC)is an important constitutive relation,which can describe the soil’s suction and stress states.Through the study of the SSCC,based on the occurrence state of pore water and the mechanism of solid-liquid interaction mechanism,with the increase of water content the SSCC is divided into different stages,and also reveals the intrinsic link between the feature points in each stage and the Consistency limits.Due to the above ideas the work of this paper is as follows:(1)Using the basic test methods to measure the soil’s liquid-plastic limit were studied,analyzing and summarizing the defects of each test method.And also a simple review of the various methods is provided for reference.(2)According to the analysis requirement,we need to reconstruct the soil samples with different initial conditions.The liquid-plastic limit of the soil is measured by the liquid-plastic limit combined method,and then the SWCC of the soil is measured by unsaturated soil triaxial instrument under different initial conditions,also analyzing the variation characteristics of the curve in different dry density and net confining pressure.According to the comparative analysis of the previous test and the test,the accuracy was confirmed.(3)Using RETC software the data of the test are fitted,and obtaining the four kinds of modal parameters,and then analyzing the transformation law of the parameters.According to the experimental data,the relation expression between the suction stress(s?)and the mass water content(w)is deduced combining the method of Lu’s,drawing and analyzing the SSCC under different dry density and the net confining pressure.Finally,according to the van Genuchten equation,the SSCC under different conditions is fitted by the least squares method,and also analyzing the SSCC.(4)The SSCC is divided into five stages,and the correspondence relation between the water content of the characteristic points of each stage and the consistency limits of soil is analyzed,and the physical nature of consistency state and consistency limits are revealed.The detailed relationship between the stages of capillary water and the liquid-plastic limit is discussed in detail.As a comparison,the test data of the existing SWCC are used to analyze the results.The results further show the feasibility of determining the plastic-plastic limit of fine-grained soil based on the SSCC.