Unsaturated shear strength properties of a compacted expansive soil from Regina, Canada

The main objective of this research was to investigate the unsaturated shear strength properties of the compacted expansive soil from Regina (Saskatchewan, Canada). Laboratory investigations on a typical expansive clay (liquid limit of 77% and plastic limit of 27%) were conducted using both saturated and unsaturated samples. Results indicated that the SWCC had one AEV of 10 kPa for w and θ and two AEVs for S: 10 and 7000 kPa due to drainage through inter-clod pores and soil matrix, respectively. Most of the shrinkage occurred around S ≈ 80%, whereas desaturation before and after this value was associated with small changes in void ratio. Likewise, the peak stress on the dry side of optimum along with the initial gradient of the stress-displacement curve of up to 250 kPa and 13,350 kPa/mm, respectively, decreased to 170 kPa and 5670 kPa/mm on the wet side of optimum. The variation in cohesion followed the compaction curve and increased from 24 kPa on dry side to 65 kPa at optimum and then decreased to 33 kPa on wet side. The friction angle followed an L-shaped trend and decreased from 44° on dry side to 29° at optimum and to 27° on wet side. Finally, the S-shaped ϕ ^b curve was in agreement with compaction characteristics and the SWCC. The ϕ ^b curve comprised 1° increase on dry side (and approaching residual suction), 12° increase around optimum (between AEV and residual suction), and 2° increase on wet side that tended to approach ϕ near saturation.