Control Of Cracks At The Edge Of The Loess Terrace On Loess's Permeability And Slope Stability

Loess is the most widely distributed special soil in Western China.Tableland is one of the most widely distributed landform types in loess area.Under the influence of unloading,various kinds of cracks parallel to the platform margin are widely distributed in the surface and loess areas of the platform margin,and the loess landslides are concentrated along the edge of the platform.Obviously,the stability of loess tableland slope is closely related to the permeability of loess,besides the control of slope topography.The latter is controlled by loess structure,especially the development and development characteristics of platform margin fractures.At present,most studies on the permeability of loess are concentrated on the homogeneous loess.The relationship between the fracture development and the permeabilit y of the Loess and the stability of the slope is still the description level of the residence phenomenon,and the systematic study is lacking.It is of great theoretical and practical significance to systematically study the development characteristics of platform margin fractures to control the permeability of loess and control the stability of platform slope.The black square is located in the salt pan gorge town of Yongjing County,Lanzhou City,Gansu Province,which is one of the typical loess tableland in Longxi area.Due to the long-term infiltration of farmland irrigation water and the tight distribution of cracks in the edge zone of the black square platform,the landslides in this area are extremely developed.Luo Jia Po is one of the typical landslides on the edge of the black square platform.In April 2015,two landslides occurred in February 2017.At present,there are still a large number of cracks on the edge of the rojiapo area,so this paper takes rojiapo loess as the research object,and constructs 22 loess samples with different cracks in the laboratory.By means of experimental means,the law of the change of the permeability of the Loess with the length of the crack and the distance from the crack to the surface is systematically studied.With the coupling of the SEEP/W module in GEOSTUDIO and SLOPE/W,the variation of the stability of the rojiapo slope with the characteristics of the fracture development is evaluated quantitatively under the condition of irrigation and the development of the Loess fracture.The main results of the paper are as follows:1)When the fracture is in the same depth,the permeability coefficient increases with the increase of crack width.When the width of the crack is the same,the closer the distance is,the greater the permeability of loess will be.At the same time,the influence of surface cracks on the permeability of loess is much greater than that of hidden cracks on the loess.Although hidden fractures will also affect the permeability of loess with depth changes,the magnitude of impact will change little.In the course of the experiment,the deeper the hidden cracks,the more easy to produce other seepage channels in the process of infiltration of the loess,so it is presumed that the influence of the permeability of the Loess may be smaller when the hidden cracks are buried too deep in the actual process.2)The deformation status of the Luo Jiapo landslide shows that landslides have been generated and the stability coefficient of landslide is Fs<1.At the same time,according to the judgment of the groundwater level and the deformation of the landslides,there are a large number of surface cracks which are larger than 6m,and there are many hidden cracks at the same time.According to the simulation results of the article,it is shown that if long continuous flooding is carried out,Luo Jia Po will slide again.