Study On The Shear Strength Of The Loess In Western Shanxi Province Under Affecting By Moisture Content And Stres State

The soil shear strength parameters play a key role in stability analysis of slope engineering, embankment engineering and excavation treatment, so studying on shear strength parameters is always a hot issue in geotechnical engineering. On the basis of collecting materials, measuring slopes and sampling in filed, by doing direct shear test and triaxial compression test of undisturbed soil under different water content, this paper with the research object of loess in west Shanxi presents different kinds of shear strength parameters of different loess lithography lithology in west Shanxi area. The test result shows that:1. The value of shear strength decreases as the water content increases in direct shear test. The curve of cohesion and water content presents like a chair, when water content smaller than about 12%,the value of cohesion decreases quickly as water content increases. And water content between about 12% and 23%, it decreases slowly as the water content increases. When the water content lager than about 23%, it decreases quickly again. The value of internal friction angle has no obvious change as water content increases. The value of internal friction angle is range from 14°to 32°. The curve of internal friction angle and clay content shows that the envelope big in the end and small in the middle as the clay content increases, and the peak appear when the clay content about 20%.2.1n triaxial compression test, shear strength parameter "c" decreases when the water content increases. With the water content less than 12%, the decreasing tendency is steep, and it is slow as the water content larger than about 12%. With the water content increasing, internal friction angle decreased linearly and has a good correlation. Meanwhile, the value of cohesion of triaxial shear strength under the same soil sample and the same water content is larger than of direct shear test, but the value of internal friction angle has no obvious law.3. According to triaxial compression test phenomenon, the failure forms of soil samples are extension failure, shear failure and creep deformation. We summarize the curve of stress and strain of the failure forms, and analysis the relationship between failure form and the stress, water content.4. Loess is divided into 27 categories through three physical indexes which are clay content, dry density and saturation. Using the data of triaxial compression of Shanxi and Gansu, we get the suggest lower value, upper value and average value of shear strength parameters. 5. We established two-dimensional model about slope with finite element software Midas based on field limited slope's geometric parameters. The shear strength parameters of different test method and water content are imported into the calculated model and the calculation results show that, slope stability analysis should adopt the shear strength parameters when water content approach to plastic limit on condition of direct shear test, and use the shear strength parameters when water content approach to 23% on condition of triaxial compression test.