Experimental Analysis And Micro Theoretical Study On The Full Suction Range Of Soil-Water Characteristic Curve

Most of the soils in the nature are unsaturated,and a large number of unsaturated laterites and granite residual soils are also distributed in Jiangxi Province.The suction of unsaturated soil has great influence on the shear strength and permeability of unsaturated soil,which has a great influence on the stability of slope,foundation and retaining structure.Because of the complexity of the suction change and the difficulty of the test,it becomes the key and difficult point in the study of unsaturated soils.Therefore,to carry out the research of unsaturated soil water characteristic curve has very important engineering significance and research prospects.The data measurement of soil water characteristic curve generally needs to be obtained through indoor test,but in the experiment,the soil water characteristic curve test is mostly used by single test method because of various factors such as equipment,test time and so on.However,it is difficult to get the soil water characteristic curve of the full suction range only by one test,and the soil water migration law of a full suction range should be analyzed in the actual project.Therefore,in this paper,the soil water characteristic curves of the full suction range are determined by pressure plate method,filter paper method and saturated salt solution method,taking Jiangxi laterite and granite residual soil as the research object.At the same time,the influence of dry density,particle diameter and drying wetting cycles on the soil water characteristic curve in the full suction range is analyzed.The most suitable mathematical fitting model for suction section and full suction range of different tests is discussed.Then the shear strength model of unsaturated soil,which is suitable for the full suction range of red soil and granite residual soil,is obtained by combining the data of the direct shear test and the soil water characteristic curve test of the full suction range.And the shear strength parameter?~b of unsaturated soils are discussed with the variation of matrix suction in the full suction range.Finally,the theoretical solution of soil water characteristic curve is deduced through theoretical analysis,and the influence of particle gradation and contact angle on micro soil water characteristic curve is analyzed.The main contents are as follows:(1)Taking Jiangxi laterite and granite residual soil as experimental objects,the basic physical and mechanical index tests are carried out respectively.By three methods of pressure plate method,filter paper method and saturated salt solution method,the soil water characteristic curves of each suction range under the influence factors of dry density,particle diameter and dry and wet cycle are measured and analyzed.Through the pressure plate test,the filter paper test and the saturated salt solution test data combination,the soil water characteristic curve of the full suction range under different factors can be obtained.It shows that this method is feasible to measure the soil water characteristic curve of the full suction range.(2)The best fitting model of soil water characteristic data fitting for different suction range and full suction range is studied.On the basis of Gardner model,VG model and FX model,the test data of soil water characteristic curve of each test suction range and full suction range under different influence factors are fitted,and the fitting results are evaluated on the basis of comprehensive consideration of the fitting precision and the number of model parameters.It is found that VG model is most suitable for fitting pressure plate test data and saturated salt solution test data.Gardner model is most suitable for filter paper test data fitting.The VG model is the most suitable for data fitting of soil water characteristic curve in the full suction range.The research also indicates that the measured data of filter paper test can better reflect the soil water characteristic curve of the full suction range if it is fitted with Gardner model.(3)The shear strength of Jiangxi laterite and granite residual soil under different dry density is tested at different dry density.The shear strength of unsaturated soil is analyzed with the previous full suction soil water characteristic curve test data.The results show that the shear strength parameter?~b of unsaturated soils are not certain,and decrease with the increase of matrix suction.Under the same low matrix suction range,the larger the dry density sample is,the larger the?~b is,but the influence of dry density decreases with the increase of matrix suction.And the relationship between the shear strength parameters and the suction matrix of the full suction range is obtained by fitting.The shear strength model of unsaturated soils under the full suction range is derived,and the correctness of the model is verified.(4)Based on thermodynamic equation and two-dimensional fluid bridge calculation theory,the theoretical solution of soil water characteristic curve of three unequal particle size soil particles is derived.The influence of particle size and contact angle on soil water characteristic curve is analyzed.The research shows that under the same matrix suction,the larger the Cu is,the smaller the volume moisture content is.In the larger section of the curve slope,the worse the gradation is,the larger the Cc is,the smaller the volume moisture content.Under the same matrix suction,the smaller the contact angle is,the larger the water volume and volume moisture content is,and the air entry value of the curve decreases with the decrease of contact angle.