UH Model For Clays And Granular Soils

Soil is the most common material for geotechnical engineering,and geotechnical problems are caused usually by deformation and failure of soil.Therefore,it is very important to research the stress-strain behaviors of soil,and the constitutive model of soil has been paid more and more attention.Due to the differences in the mechanical behaviors of clays and granular soils,the corresponding constitutive models are also different.However,clay layers and granular soil layers distributed alternately in practice.Therefore,the study on unified constitutive model for clays and granular soils has been a research focus in soil mechanics to facilitate analysis and solve geotechnical problems.In addition,the shear strength of clays and granular soils has been described uniformly.If the stress-strain relationships between clays and granular soils have been also unified described,the constitutive theory and soil mechanics will be promoted.Therefore,it is of great theoretical value to develop a simple unified constitutive model for clays and granular soils.Based on the unified hardening(UH)model for overconsolidated soils,a constitutive model for clays and granular soils,referred to as CSUH model,is first developed by combining the unitifed normal compression line(NCL)equation of calys and granular soils,drop-shaped yield surface and dilatancy equation.Based on the relationship between location of the critical state line(CSL)and stress Lode angle,the CSUH model is then generalized to the three-dimensional(3D)stress condition by the transformed stress(TS)method.Finally,the CSUH model is extended to describe the behaviors of granular soils at extra-large stress level by adopting a limit void ratio.CSUH model:Firstly,by introducing a crushing stress(p_s)into the NCL equation of UH model,the unified NCL equation of clays and granular soils is established.Secondly,a drop-shaped yield surface is proposed by introducing a critical state parameter(?)into the elliptic yield surface.Thirdly,the effect of the current state on the dilatancy is considered by incorporating a dilatancy parameter(m)and a new state parameter(?)into the dilatancy equation of the UH model.The CSUH model is developed by combining the unified NCL equation,the drop-shaped yield surface and the dilatancy equation.When crushing stress p_s,critical state parameter?and dilatancy parameter m are all equal to 0,the CSUH model degrades to the UH model,and further degrades into the modified Cam-clay model when the overconsolidation ratio is equal to 1.3D-CSUH model:Test results have shown that the location of CSL is related to the stress Load angle.Based this phenomenon,the relationship between location of the critical state line(CSL)and stress Lode angle is then established and introduced into the CSUH model.Meanwhile,the CSUH model is then generalized to the 3D stress condition by the transformed stress(TS)method.Comparisons with test data indicate that the CSUH model not only can describe the behaviors of normally consolidated clay and weak/heavy overconsolidated clay,but also can describe the behaviors of granular soils consisting with large particles or small particles,especially the static liquefaction of sands.CSUH model reflected for extra-large stress:A limit void ratio of soil is achieved at extra-large stress.The stress-strain relation of normally compressed soil under the isotropic compressed condition is built by introducing the limit void ratio into the NCL equation of the CSUH model.By incorporating the stress-strain relation,the drop-shaped yield surface and dilatancy equation of the CSUH model,the CSUH model is extended to describe the behaviors of granular soils at extra-large stress level.Comparisons with test data of granular soils with in the confining pressure range from 0.4MPa to 68.9MPa indicate that the extended CSUH model can describe the behaviors of granular soils at low stress,medium high stress and(extra)high stress level.