Experimental Study Of Unsaturated Silt Critical State

The critical state of soil is one of the most important concepts in soil mechanics. The soil critical state gives the end of soil deformation process, which is very important for analysis and establishment of the constitutive model of soil. Although the critical state of unsaturated soils was applied in to a number of constitutive models, but its basic definitions and its sufficient conditions which is needed to be met are not clearly given out and relevant test results is extremely scarce. Thus, changes in the law of each state parameters and the basic conditions needed to meet the critical state is reached, the test data will provide support when using the test methods, in unsaturated soils subsequent critical state theory, non-saturated soil engineering problems analyze and solve theoretical basis.Non-saturated silt was used for the study, the unsaturated soil triaxial testing system (GDS) and saturated soil automated triaxial test apparatus were used to study the soil in different dry density under different net stress and suction conditions to critical state,the variation of the soil strength, volume change, water content and saturation and other related state parameters were indicated.On the basis of analyzing and summarizing the experimental data, the establishment method of the critical state theory of saturated soil is established, and the characteristics of unsaturated soil are analyzed, based on the basic conditions to give unsaturated soil shear critical state to be fulfilled, and the establishment of different coordinate plane unsaturated soils critical equation of state specific research results are as follows:1. For each of the state variables for unsaturated silty sand certain initial dry density by undertaking different net stress, triaxial shear tests under different suction the critical state state variables (such as migraine stress, specific volume average net stress, pore water volume ratio, etc.) were obtained. The variation curves reveal the basic condition for unsaturated silty sand and critical state shear to be fulfilled. The results showed that: (1) With the increase of axial strain, different initial dry density silt sample bias stress, physical strain and saturation curve tends to a final stable value; (2) the shearing process the degree of saturation were mainly affected by the variation of the volumetric strain, less affected by changes in water content. Based on the above experimental law, the degree of saturation was analyzed as a suitable evaluation index for critical state condition which means:under the condtion of small water content changes before and after shearing or good permeability of the sample during unsaturated soil shear process, the degree of saturation can be considered as a evaluation index for sample to judge the critical state condition.2. For different initial dry density of unsaturated silty sand, triaxial shear tests were carried out under different stress conditions, comparative analysis of different changes of initial dry density of the sample in the shearing strength and volumetric strain verified for loose sand, their typical mechanical properties of dense sand. The results showed that:dry silt density 1.96g/cm3 exhibits dilatancy and strength characteristics after the peak began to soften; silt dry density 1.6g/cm3 is manifested as loose sand shear shrink characteristics, as well as continued strength characteristics sclerosis.3. Based on the test results of the above studies, the establishment of a q-p’, v-lnp’, vw-lnp’critical state line equation in the plane, presented from three aspects strength, deformation and pore water of unsaturated silt critical the method described in the state comprehensive, revealing the strength of unsaturated silt under critical state conditions, void ratio, pore water variation with the suction volume ratio. The results showed that: (1) q-p’plane of unsaturated soil slope of critical state line suction Ms not affect the size equal to saturated soil slope of critical state line M; intercept μ is the suction function, with different suction The change. (2) v-lnp’plane of unsaturated soil slope of critical state line from suction on λs, equal to the size of the critical state line saturated soil slope λ; intercept F is a function of suction, change with different suction. (3) vw-lnp’ unsaturated soil in the plane of critical state line slope λw and intercept Fw is saturation (suction) function, the function coefficients are equal to X and F.