Shear behavior and microstructural variation in loess from the Yan'an area, China

Abstract The shear behavior of loess is closely related to its microstructural variation. Their relationship is of great significance to better understand the loess landslide mechanism. Consolidated-undrained triaxial tests were performed on natural loess from Yan'an, China, with various initial water contents under different confining pressures to investigate the shear behavior. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were conducted on the specimens before and after the triaxial tests to study the variations in microstructure and pore characteristics and their relationship with the shear behavior. The triaxial tests revealed three different failure modes (shearing, homogeneous and plastic failure) and the corresponding stress-strain response of specimens depending on confining pressure level and initial water content. The cohesion decreases exponentially with increasing initial water content whereas the internal friction angle decreases slightly. This effect is closely related to the weakening effect of water on the inter-particle cementation and water-air interface in loess. The macroscopic shear behavior of loess is essentially the result of the continuous adjustment and change in its microstructure system under loading and wetting. This variation process is related to the confining pressure, initial water content and failure mode of the specimen. This condition is manifested by the softening, dispersion, disintegration and reassembly of cementations, particle movement and rearrangement, the reduction and mutual transformation of the inter-aggregate pore populations larger than 0.05 μm in diameter (macropores and abundant mesopores decrease, small pores increase), and the generation and development of cracks under certain conditions.