Fractures are widespread phenomena on loess slopes in northwestern China. Fractures are of various types and have different distribution patterns, and they are important factors affecting the mechanical properties of loess. In this paper, the effect of different fracture distribution modes (fracture angle, fracture position and fracture combination) on the shear strength of loess is investigated by carrying out consolidated undrained triaxial shear tests. The results show that the existence of fractures in loess can significantly weaken the strength of the soil under consolidated undrained conditions. Compared with unfractured loess, fractures weaken the shear strength of loess mainly by weakening the cohesion. The internal friction angles of fractured loess, however, are hardly affected by the existence of fractures and the fracture distribution mode. Furthermore, a comparison of three fracture distribution modes, namely, the fracture angle, position and combination, reveals that the fracture angle is the most significant factor weakening the loess strength, followed by fracture combination, and the least is fracture position. In addition, confining pressure increments can greatly improve the shear strength of both unfractured and fractured loess, and confining pressure increments can inhibit the weakening effect of fractures on loess strength.
It is of great signi cance to study the time-dependent mechanical properties of loess, as loess landslides are closely related to them. The purpose of this study is to investigate the effect of moisture content on instantaneous and time-dependent deformation, strength and failure behaviors of undisturbed loess specimens from Nangou in Yan'an City, Shanxi Province, China, via triaxial shearing tests and multi-loading triaxial creep tests under moisture contents of 5%, 10%, 17% and 22%. The results show that the timedependent deformation of loess increase with the moisture content, while the time-dependent deformation rate decreases slowly. The soil deformation is divided into four stages based on the peak strain rate. Furthermore, the instantaneous and long-term strength of loess decrease with increasing moisture content, and the instantaneous strength decreases more than the long-term strength. The failure mode of undisturbed loess changes from shear failure to homogeneous failure with increasing moisture content; when the failure mode is shear failure, the thickness of the shear band that forms at the specimen surface over time is smaller than the corresponding thickness that forms instantaneously. Finally, the macroscopic morphology and microstructure of loess specimens were considered together to analyze the effect of moisture content on the instantaneous and long-term mechanical behavior of loess and to discuss the process of loess deformation to failure.
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