Competing effects of wetting and volume change on G in compacted loess

This paper explores the relative contributions of wetting (suction reduction) and its associated volume change on the small-strain shear stiffness, G₀, in compacted loess from Xi’an, China. Results from one-dimensional compression tests with measurements of the shear wave velocity upon wetting and loading paths are presented. The experimental results show that the softening caused by wetting compete with the densification caused by plastic deformation and their effects on G₀ are strongly controlled by stress level applied prior to wetting. Below the compaction stress, suction effects are dominant and G₀ reduces irrespective of the magnitude of the collapse strain. With the increase in the stress level, the reduction in G₀ caused by saturation is compensated by the plastic deformation triggered by soil collapse. This behaviour is clearly observed when the soil is first loaded to the compaction stress, where the maximum collapse strain is measured upon wetting. Volume change is dominant once the compaction stress is exceeded so that G₀ tends to increase upon wetting. A wetting-induced stiffness factor D is defined to demonstrate that the change in G₀ varies linearly with the stress level and this behaviour is independent of the compaction conditions.