Anisotropy Of Shear Strength Of Undisturbed Malan Loess

Loess is a kind of special structural soil,which is mainly affected by the formation environment and stress history environment,and there are obvious pore structure and vertical joint.The horizontal stratification,the porosity and vertical joints lead to obvious anisotropy of mechanical properties of loess.And for different areas of loess,the mechanical properties under the influence of different factors are also different.The area of loess and loess-like soil on the earth is about 13 million km2,accounting for more than 9% of the total area of the global continent.And loess is widely distributed,especially in the Midwest and the Northern part of China.With the implementation of the national strategy of "West development" and "The Belt and Road",the number of projects in loess area is increasing day by day,and the scale is gradually expanding.In the construction of highway,railway,bridge,tunnel and other transportation infrastructures,various of problems of loess will appear.Therefore,the study of mechanical properties of loess is becoming more and more important.The samples used in this paper are undisturbed Malan loess taken by artificial exploration pit.Based on previous researches about shear strength and anisotropy of loess,the anisotropy of Malan loess in this area is explored and the reasons are discussed through the physical test of dry density,void ratio,particle weight,liquid plastic limit,particle size analysis and laboratory direct shear test.The sample used in the direct shear test is the dry undisturbed Malan loess(the moisture content is 0).Then the standard cylindrical samples were obtained through the cutting by wire cutting machine and polishing of fine sand paper.Direct shear tests were carried out on the samples taken from 7 pits respectively in three directions: vertical,east-west(strike)and north-south(dip)direction.Three samples were cut in each direction,and 63 groups of direct shear samples were used.The shear strength and the vertical displacement during the shearing process were measured respectively.The results show that the Malan loess in this area is obviously anisotropic.For the undisturbed Malan loess in this area with 0 moisture content sheared from different directions,there is no obvious law of the vertical displacement of the sample during the shearing process.The vertical density and shear strength are obviously greater than that of the horizontal direction,and the vertical shear strength is about 1.15 times that of the horizontal direction.There is little difference in the shear strength between the east-west(strike)and north-south(dip)direction.It can be concluded that the vertical joint and pore structure have more obvious influence on the mechanical properties of Malan loess in this area.