A Study On The Effect Of Clay Content To The Liquefaction Resistance Of Sand

Rainfall, earthquakes and improper development of human are likely to induce the landslide hazard, of which the landslide triggered by rainfall and earthquakes is most common and usually leads to heavy casualties and property losses. China, a mountainous country with plentiful rainfall and frequent earthquakes, is one of the countries in which landslides happen frequently in the world, and suffers great economic losses every year for this. In recent years, due to the need of national economic construction, a lot of artificial slopes are backfilled or excavated in our country. These slopes are not only composed of sand but the fines including silt and clay. For years, field and laboratory studies have shown that, sand with a certain amount of fines, has properties similar to liquefaction of loose sand under certain conditions. Therefore, the study of liquefaction and stability of slopes containing fines under the rainfall and earthquake has a very important realistic and engineering significance in the prediction and prevention of landslides. While the nature of silt is close to sand, clay content can be directly used in considering the effect of fines content on the liquefaction resistance of sand. Accordingly, this paper will focus on the study of influence of clay content on the liquefaction resistance of sand, mainly including the following aspects:1. Both relative density and confining pressure have an important impact on the liquefaction of sand. This paper conducted a series of CU tests of clean sand with different relative density under different confining pressure on the static tri-axial apparatus. The result of tests shows that clean sand is prone to static liquefaction at low relative density and high confining pressure.2. The presence of clay will affect the liquefaction resistance of sand. Therefore the CU tests were done on the saturated sand with different clay content at the same relative density under different confining pressure in this article. The results indicate that the influence law of clay content on the liquefaction resistance of sand is not monotonous under static loading. The curve of shear strength with clay content appears to be a parabola opening upward with a valley value. The sand is most vulnerable to static liquefaction at this value for the shear strength is smallest and thus the liquefaction resistance of sand is the worst. The clay content corresponding to this value should be between5%and10%, while it turns out to be5%in this paper. The reason for this is that the number of groups of clay content considered in the experiment is too few. 3. To investigate the effect of clay content on the liquefaction resistance of sand under cyclic loading, the dynamic tests were firstly done on the specimens with different clay content through the bi-directional vibration three-axis machine named Tian shui hong shan. Then the results were verified by CKC tri-axial instrument under the same confining pressure of200kPa. The relative density of specimens is kept at20%. It can be concluded from the tests that the influence law of clay content on the liquefaction resistance of sand under cyclic loading is the same as the one under static loading, which is not monotonous.4. The instability of slopes in nature and engineering practice is often induced by the static liquefaction caused by continuous rainfall. Based on the permeability characteristics of unsaturated soil and the basic theory of rainfall infiltration, as well as the result of CU tests, the numerical simulation was made by Geostudio in this paper. The simulation demonstrates that the influence law of clay content on the stability of slopes is not monotonous. The curve of safety factor with clay content is a parabola opening upward.