Study On The Soil Water Characteristic Curve And Strength Characteristics Of Unsaturated Loess In East Gansu Province

Longdong area is a typical unsaturated loess area with the most completely preserved and the largest area of loess tableland in China,it also has very important research value.However,because of various reasons,the researches on loess in the northwest region are usually concentrated in Lanzhou,Xi'an and other places in the past,there are few researches in Longdong area.Therefore,in this paper,the study is focused on the experimental study and theoretical analysis of soil-water characteristic curve and strength characteristics of Q3 unsaturated loess in Longdong area,which is supported by the building science and technology project of "Super thickness characteristic loess structure and foundation optimization research"(Grant No.JK2014-34)from Gansu province.And the main work and results obtained are as follows:(1)The effects of initial dry density and net mean stress on the soil-water characteristic curve of unsaturated loess are studied.The results show that: When the matrix suction is the same,the moisture content of samples decreases with the increase of net mean stress.The larger the initial dry density is,the smaller the moisture reduction rate is,and the higher the final moisture content is.Through the Van Genuchten model,it can be found that the residual volume moisture content ?r decreases with the increase of net mean stress.The fitting parameter ? and n do not change significantly as the net mean stress increases.The initial dry density mainly has an effect on the parameters ?r and ? of soil-water characteristic curve,but the parameter n is less influenced.(2)The triaxial consolidated drained shear tests are studied on the intact loess and remolded loess in Longdong area,in which the matrix suction and the net confining pressure are constant.The results show that: within the range of matrix suction and net confining pressure in this paper,the matrix suction is certain,when the net confining pressure increase,the curve(?1-?3)-?1 of intact loess gradually changes from the weak hardening model to the hardening model.With the increase of initial dry density,the curve(?1-?3)-?1 of remolded loess gradually evolves from the strain hardening model to the ideal elastic-plastic model and finally to the strain softening model.With the increase of matrix suction,the suction friction angle ?b of intact loess gradually decreases,the cohesion and internal friction angle increase nonlinearly,but the internal friction angle dose not increase significantly.The suction friction angle?b of remolded loess increases with the increase of initial dry density.The matrix suction and initial dry density mainly have an effect on the shear strength of soil by affecting the cohesion of remolded loess.(3)The predicted value of shear strength of intact loess is obtained by soil-water characteristic curve.By comparing the predicted values to the measured values,the accuracy of the predicted formula and the cause of error are analyzed.Finally,based on the measured values of shear strength,the shear strength formula of unsaturated intact loess in Longdong area is obtained by mathematical fitting method.