Study On Properties Of Strength,water Drainage And Deformation Of Unsaturated Undisturbed Loess In Constant Suction Triaxial Test

Based on the theory of unsaturated soil mechanics,the characteristics of strength and the characteristics of deformation and the informations of change of water of undisturbed Q₃ loess in Yangling were studied through conducting conventional triaxial test of unsaturated undisturbed loess and triaxial test for equal suction of unsaturated undisturbed loess with GDS stress path triaxial apparatus and AutoPore IV 9500 mercury injection apparatus.The following main research contents and innovative conclusions are obtained:?1?The isotropic consolidation test and the conventional triaxial drainage shear test and isobaric consolidation test and triaxial drainage shear test for equal suction were carried out.The test results show that when the suction are the same,the volume deformation in consolidation shear tests improved with increase of net confining pressure and when the net confining pressure are the same,the volume deformation in consolidation shear tests improved with increase of suction.On the other hand;when the suction are the same,the strength of samples improved with increase of net confining pressure,with decreaing of void ratio after consolidation;when the net confining pressure are the same,the strength of samples improved with increase of suction.,but with increase of suction.In general,the positive effect of suction on shear strength is greater than that of porosity ratio on shear strength.In addition,CSL lines of loess samples with different suction were presented in the p-q plane,and it was found that CSL lines of saturated soil gradually exceeded CSL lines of unsaturated soil under low suction.The reason was that with the increase of p value and the increase of net confining pressure,the decrease of porosity ratio of saturated soil was gradually greater than that of unsaturated soil.The contribution of small porosity ratio to shear strength is gradually greater than that of unsaturated soil suction to shear strength.?2?The informations of change of water on constant suction consolidation shear test were recorded and analyed with the soil water characteristic curve models proposed by HUANG et al.,HU et al.and Fang et al.The test results show that shear rate has an effect on displacement and the first two models are suitable for the case with slow shear rate and sufficient drainage when fitting the model parameters proposed by HUANG et al.,HU et al.with the data after consolidation test and the predicting the shear displacement.The model parameters proposed by FANG et are impacted by shear rate.?3?Mercury injection experiment?MIP?were carried out with the samples which experience the different stress path test to study the variation law of microcosmic pore characteristics of loess.A loess deformation calculation method based on the variation of pore distribution was established with the macroscopic mechanical conditions of the sample.The results show that there is a strong correlation between the scaling of the peak in the pore distribution curve and the sample deformation,and a loess deformation calculation method with Barcelona hardening parameter as the stress state variable and intergranular porosity ratio as the strain state variable is established.