Featured Application This research paper encourages repurposing waste material for ground improvement. The results of this study contribute towards a greater understanding of the strength and durability performance of treated soils under normal, fluctuating, and adverse moisture conditions.Abstract Expansive soil underlying structures pose a significant risk to the integrity of superstructures. Chemical soil stabilization can be used to strengthen soils due to the cost and impracticality of mechanical approaches. Waste materials such as recycled gypsum and rice husk ash have been considered alternatives because of their sustainable and economic advantages. A combination of these additives was used to address the high absorption of gypsum and the lack of cohesion of the pozzolan. The study assessed the short-term and long-term performance of expansive soil treated with recycled gypsum and rice husk ash under normal and fluctuating moisture conditions. Direct shear tests indicated ductile and compressive soil behavior with improved shear strength. A good approximation of stress-strain response was made with a modified hyperbolic model for treated soils that exhibited strain hardening and compressive volumetric strain. Durability and water immersion tests were performed for samples after varying curing periods and cycles of capillary soaking to assess the behavior when exposed to varied environmental conditions. Samples under the modified durability test experienced significant strength loss, with decreasing compressive strength as curing durations increased. Specimens in the modified water immersion test experienced significant strength loss; however, it was determined that curing durations did not contribute to the change in the strength of the sample. Expansion index tests also determined that the treatment effectively mitigated expansivity and collapsibility in all samples. Despite improvement in shear strength and expansion potential, further investigation is needed to enhance the durability of soil treated with gypsum and rice husk ash.

By conducting undrained cyclic triaxial tests on fibre-reinforced very loose and loose saturated sand, we investigated the build-up of excess pore pressure and the flow liquefaction responses. The test results show that unreinforced very loose and loose saturated sand has a high potential for liquefaction, with flow liquefaction occurring in all unreinforced samples under undrained cyclic loading. The presence of fibre reinforcement has a positive impact on the resistance to flow liquefaction of sand. Fibres provide both a densifying effect and a confining effect to the sand skeleton. However, the confining effect of fibres depends on the loading path imposed on the samples and the deformation mode of the samples. The presence of fibres alters the evolution law of the residual excess pore pressure in saturated sand. When fibres impose a strong confining effect on the sand skeleton, the evolution of residual excess pore pressure along with the normalized loading cycles follows a curve with an 'inverted L' shape, being significantly different from an 'S' shape curve which is followed by the unreinforced sand. Under the two-way symmetrical and one-way cyclic loading, the significant fibre stress contribution is mobilized, leading to the effective stress of the sand skeleton being much greater than 0 after the 100% build-up of excess pore pressure. As a result, the strength loss of the reinforced sample remains below 11% and thus the fibres prevent liquefaction from developing.