Study Of The Water Content Effect On Shear Strength Of Loess Slope In Gan Su Area

Loess in Gan Su area has a wide distribution and a large thickness, which is more than 300 meter in some area. Controlled by stratum lithology, the engineering geology problems is very serious.So the stability analysis is necessary in slope engineering, embankment engineering and excavation treatment etc. The shear strength parameters are the essential index in engineering stability analysis.Studying on shear strength parameters has been got a very important significance.By the measurement of limit slope, sampling and doing direct shear test and triaxial compression test of undisturbed soil and repeated shear test of remoulded soil under different water content, this paper presents three kinds of shear strength parameters of loess in Gan Su area. The test results show that:1.In direct shear test, the water content has a larger effect on the cohesion and has a relatively small effect on the internal friction angle; However in triaxial compression test,the water content has a larger effect not only on the cohesion but also on the internal friction angle. It shows that the internal friction angle has the largest value when the soil has the middle water content, but has a small value when the soil has a smaller or larger water content. It is result from the different failure modes of soil of direct shear test and triaxial compression test:In direct shear test, the shear plane is inherent; but in triaxial compression test, the failure mechanism varies with the water content, the shear plane is not inherent, and the normal stress of the shear plane varies relatively large.2.According to the result of repeated shear test, the value of cohesion of residual shear strength is close to zero, which doesn't vary with the water content. But the value of internal friction angle decreases with the water content and clay content increases.It is shown that the value of cohesion is determined by the structure strength, and the value of internal friction has great relationship with the clay content and soil particles oriented arrangement during the shear process.3.Based on the back analysis of the limit slope, a correction method of direct shear strength is proposed. In the paper we use the shear strength parameter of triaxial compression test under the starting water content to correct the direct shear strength parameter. The results show that the correction value of cohesion of the direct shear strength decreases as the liquid limit and plastic limit and clay content increases, but the internal friction angle doesn't effected by these index. The correction value referred a method to slope protection design and treatment.