Strength Study Of Unsaturated Soils Based On Microscopic Properties Of Pore Water

With economic development and increasingly developed infrastructure,unsaturated soil engineering theories are facing more and more challenges in engineering practice,and the study of engineering properties of unsaturated soils has become a popular topic for researchers both at home and abroad.Existing research has developed numerous strength theories,but their applicability conditions as well as their accuracy are influenced by soil type and many extraneous variables.For the study of shear strength of unsaturated soils,the Bishop effective stress coefficient theory and the Vanapalli and Fredlund dual stress variable theory have been applied more often.In this study,the shear strength of Wuhan clayey soil is investigated based on the Bishop effective stress principle.In the existing studies,the effective stress coefficient is usually associated with soil saturation,and the concepts of saturation S,effective saturation Se,and capillary saturation coefficient Scap have been proposed in turn throughout the exploration of the values of effective stress coefficient.In recent years,researchers have found that the accurate classification of pore water types in soils and the definition of the form of contribution of various water to soil strength are important processes in determining the effective stress coefficient.In this paper,the relationship between adsorbed water content in soil and matrix suction,i.e.,the adsorption water retention curve(AWRC),was determined by volumetric bottle method tests,indoor evaporation tests,and low-field NMR tests on clayey soils in Wuhan.The capillary water retention curve(CWRC)can be obtained by extracting the AWRC from the soil water characteristic curve.The obtained CWRC was applied to the shear strength prediction of Wuhan clayey soils with dry densities of 1.50g/cm3,1.60g/cm3 and 1.70g/cm3.The shear strength of the three dry density soil samples when subjected to four sets of matrix suction was measured using a common triaxial meter and a GDS unsaturated soil triaxial meter.The measured and predicted values were compared,and the accuracy of the prediction results was evaluated using the root mean square error(RMSE).The results showed that the predicted shear strength values obtained by the NMR method were more accurate compared with the other two methods,and the prediction accuracy was less sensitive to the dry density of the soil samples and the surrounding pressure.