Plane Strain Test And Landslide Mechanism Analysis Of Loess From Zizhou Of Northern Shaanxi

Loess is widely distributed in Midwestern China, and northern Shaanxi plateau isimportant component of the world famous "loess plateau". In recent years, the geologicalhazards in loess regions are frequent because of the special formation and the typicalcharacteristics of loess, as well as the geological movement and the increasingly frequenthuman engineering activities. With the characteristics of large-scale, strong hazards, difficultto predict, loess landslide now has become one of the serious geological disasters whichseverely limits the economic and social development of the loess areas. For the specialproperties and the typical structures of loess in northern Shaanxi, the problem of loesslandsilde in northern Shaanxi there is particularly urgent. Therefore, it is essential for theeconomic development and the safety of people’s lives and properties to provide reasonableand reliable designing indicators and parameters of soil through comprehensive experimentaland theoretical investigation of loess landslides.Based on the reformed TS-526multifunction triaxial apparatus, this paper carried out theplane strain test and the unilateral limit plane strain tests which simulated the free face oflandslide of loess from Zizhou of northern Shaanxi. It analyzed deformation and strengthcharacteristics of loess under different initial state parameters as well as the localizeddeformation. And it tried to explore mechanism of loess landslide of Zizhou according to theexperimental conclusions. The main conclusions of the paper are as follows:(1) Deformation and strength characteristics of Zizhou loess under plane strain conditionIn plane strain tests, the specimens did not show obvious localized deformationproperties, and the stress-strain curve of soil mainly reflected hardening type. The volume ofspecimens showed contractive phenomenon at first, and then showed dilatation during theprocess of shearing.Other conditions being the same, the strength of the intact loess is greater than theremodeled loess. With the confining pressure and dry density increase, the strength of loesshas a remarkable increase when other conditions are the same. The contribution of the internalfriction angle to strength is more obvious under low cohesion of soil. When the moisturecontent locates in a certain range, the angle of internal friction and cohesion force change a little, but decreased significantly in the case of nearly saturated moisture content. Matrixsuction of the specimens has a increase tendency when the confining pressure increases or themoisture content decreases. And when the dry density increases, the matrix suction decreases.(2) Localized deformation under plane strain tests with unilateral limit conditionUnder unilateral limit conditions, the specimens did not show obvious localizeddeformation properties, the stress-strain curve reflected softening type when moisture contentis lower, and the stress-strain curve reflected hardening type.All samples during the shear process in the shear zone, various forms of shear bands,shear bands began to appear before the peak of the axial stress and axial strain curve, and theformation after the peak. Shear band inclination randomly distributed between59°to70°.(3) Landslide mechanism analysis in sandy loess regionThe landsilde in this region is mainly because of the steeper slope, larger internal frictionangle, as well as small conhesion in the natural state. And the stability always depends on thelimited conditions, water, human activities and climate change,etc.The landslide mechanism in Zizhou region may be due to the soil itself, and punchinginfiltration as well as artificial excavation which makes the internal stress redistributed. Thiscan induce plastic deformation in the slope foot where the shear stress concentration happens,also the shear band generation as well. In the long term influence of water flow and rainfall,plastic deformation is formed and begins to concentrate. In addition, freezing and thawingenhance the development of the shear band due to ice spilt. As a result, the shear band iscontinuously going along a certain direction and the landslides appears.