Performance assessment of highly expansive soil‒sand mixture for pavement subgrade

Expansive soils cause damages and distortions to pavements as they swell and shrink. The present study aims to develop an understanding of the mechanical stabilisation of highly plastic expansive soil with sand. The expansive soil was mixed with a wide range of sand fractions, and a series of controlled tests were performed. The results show that the addition of sand can lead to reduced plasticity, swelling and shrinkage. For example, sand inclusions (40%–80%) reduced the swell potential from 124% to a range of 80%–9% and the swell pressure from 850 kPa to 608–150 kPa, representing improvements of 35%–93% and 28%–82%, respectively. Microstructural study indicates that sand aggregates tend to form a likeskeleton-like structure that tends to share increased loading giving rise to enhanced performance. The CBR values indicate that increasing the sand content (40%–80%) improved the bearing resistance of the expansive soil by 87%–452%. Correspondingly, the resilient modulus is found to have increased by 117% to 558%, respectively. A mechanistic-empirical analysis indicates that sand blending of expansive soil subgrades can lead to reduced pavement thickness.