Deformation, strength and water variation characteristics of unsaturated compacted loess

The bearing capacity and safety of geotechnical structures are determined by the shear strength of soil. Soil is usually unsaturated in nature, and variation in unsaturated strength is very complicated. To investigate the unsaturated shear strength characteristics of compacted loess, a series of triaxial consolidated shear tests were conducted on compacted loess from the 6th loess layer in Yan’an, China, using GDS unsaturated soil triaxial apparatus. The saturation, volume and moisture change of compacted loess were analyzed, and the influence of matric suction (ua-uw) and net confining pressure (σ3-ua) on the deformation and strength characteristics of compacted loess were discussed. It was found that the deviatoric stress versus deviatoric strain curves exhibited a strain hardening state, and the volumetric strain transitions from shear contraction to shear dilatancy. In the testing pressure range (ua-uw ≤ 100 kPa, σ3-ua ≤ 400 kPa), both matric suction and net confining pressure significantly influence the deformation and strength characteristics of compacted loess. Under certain matric suction conditions, the shear strength of the compacted loess increased with increasing net confining pressure, the peak value of the shearing shrinkage increased, and the shear dilatancy decreased. Under a constant net confining pressure, the shear strength increased with the increasing matric suction. However, the peak values of shearing shrinkage and shear dilatancy decreased with increasing matric suction. In the unsaturated shear test, φ increased with the matric suction. The cohesion of unsaturated soil is affected by many factors and the data points from this research are limited owing to time constraints, hence, further analysis of cohesion strength is needed. The data used to support the findings of this study are available from the corresponding author upon request.