Deterioration of a compacted soil due to suction loss and desiccation cracking

This paper presents the results of laboratory testing of a clayey soil taken from a road subgrade in Tanzania. The results revealed a reduction in the soil water retention capacity, accompanied by shifts in the water retention curves with successive cycles. These changes affected the soil response to shear loading, resulting in decreased shear strength and stiffness with hydraulic cycles. While the soil experienced suction losses due to desiccation cracks and hysteresis effects, these suction variations alone could not account for the observed changes in shear strength, implying that the development of desiccation cracks contributed to reduced strength and stiffness. The results showed that the degradation effect of crack development on the shear strength and elastic modulus of the soil during hydraulic cycles could be justified using a macroscopic degree of saturation, i.e. the degree of saturation of large pores external to the aggregates, through a microstructural-based effective stress approach. This allowed the increase in the large pores resulting from crack development to be accounted for and hence the successive reductions in shear strength and stiffness with drying-wetting cycles. These deterioration effects need to be considered for design of geotechnical infrastructure to ensure stability, and resilience of infrastructure over time.