Experimental Investigation Of The Relationships Between Stress State Variables And Critical State Equations For Unsaturated Sandy Soils

Unsaturated granular soil is one of the widely exist materials in geotechnical engineering practice.Many experimental and theoretical researches in unsaturated soils are required for a better understanding of the mechanical behavior of the sandy soils.The principal objectives of this research were to investigate the critical state behavior for unsaturated sandy soils.The following contributions are given in the1.First,based on the local equilibrium thermodynamics theory,the author gives the necessary conditions for the unsaturated soil to reach the critical state.The research indicated that,in addition to the conditions required for the critical state of saturated soils,the state variables such as suction,saturation,and pore pressure are also constant in the critical state for unsaturated soils.The conditions proposed in this study are more complete and have a rigorous theoretical basis.2.Secondly,the author carried out a series of triaxial tests under drained and undrained conditions on unsaturated sand soil,undrained test,in order to reveal the unsaturated sand under different stress path of the mechanical behavior.Based on the experimental results,the author presents the expression of the relationship between the unsaturated sand and the critical state.These expressions define the variation of the partial stress,the ratio of the volume to the water,with the net stress,the matrix suction and the saturation.3.Finally,we present a comparison between the proposed critical state expression and the other eight critical state relation expressions.In the process of comparison,the experimental results in this paper are used to fit the experimental results of the critical state for the unsaturated sand.The comparison shows that the model is better fitted with the test results because of the influence of suction and saturation.