Ring Shear Tests On Strength Properties Of Loess In Different Regions

Landslides, slope instability and other phenomena are the result of the formation and development of slip zone soil and it has an important role for the study of the development of landslide deformation, slope stability evaluation. But when the landslide started, the deformation and the destruction of initial structure generated under the shear stress, then it should be take the residual strength as the soil strength. On the one hand, loess is a kind of soil with the special nature, on the other hand, with the widely distribution in our country and the varied deposition situation, the loess characters are diverse in different regions, leading to its strength properties are also significantly different, so the analysis and research of different loess residual strength has important academic and engineering significance for the stability analysis of the slope and the comprehensive prevention and control of the landslide.Taken the loess in Jingyang, Zizhou and Lanzhou as the research objicts,this paper carryed out the ring shear tests with different moisture content, dry densities, effective normal stress and shear rate by HJ-1 type ring shear apparatus, the main conclusions are as follows:(1)Effect of different factors on the three loess of peak strength and residual strengthThe impact of effective normal stress on the three loess of strength characteristics is unified. At the start of the test, the shear stress increases rapidly reached the peak strength, the higher the effective normal stress, the larger the achieved residual strength. With the high moisture content and effective normal stress, the sample was extrude out of the shear box during the shear test.The moisture content affected on the three loess both the peak strength and the residual strength, mainly showed that with the low moisture content, the peak strength was high, but with the higher of the moisture content, the residual strength taken a trend of first decrease and then increase.In this test, dry densities has little effect on the residual strength of the three loess, the main reason is that the density is similar after the particles form a new orientation near the shear zone.The peak strength is close under different shear rate, so the shear rate has no effect on the peak strength of the three loess in this test, but the needed time to reach the peak strength is different, while the shear rate has little effect on the residual strength.Summarizes four factors on residual strength found that the effective normal stress has more obvious effect on the residual strength, followed by the moisture content, shear rate, dry density.(2) Comparison of residual strength in different regions of loessCompared the loess residual strength of three areas, it is shown that for Lanzhou loess with a large amount of silt content, the residual strength is larger when the moisture content is 19%, for Zizhou loess with lots of coarse content, the residual strength is greater when the moisture content is less than the optimum moisture content while the dry density is 1.63g/cm~3, for Jingyang loess with a number of clay content, the residual strength is more considerable when the moisture content and dry density are little.Compared the average value of residual cohesion and internal friction angle in three regions of loess, it was found that the magnitude relationship is just opposite. The brittleness indexes are all small, and the phenomenon of softening is not obvious, in addition, there are some no softening.