Expansive soils, known for their momentous volume changes in change to moisture variations, pose problems for construction and infrastructure projects. Common stabilization methods and techniques generally have high costs and environmental impacts. The research thoroughly examines the physical and chemical interactions between the identified industrial byproducts and agricultural waste in the soil. Coal ash and RHA have been used in this study from (0, 5, 10, 15, 20, and 25%), as it is considered a waste material and, at the same time, a good adsorbent. The rice husk ash increases pozzolanic activity and lessens the behavior of soil swell-shrink. The findings of the laboratory tests show that adding these materials significantly increases the soil’s strength, durability, and stability. As the CA and RHA content increases up to 25% each, the liquid limit decreases from 41 to 29%, and the plasticity index reduces to 2%, indicating a marked improvement in soil stability. The maximum dry density peaks at 1.88 g/cm3 with a 25% CA + 25% RHA mix, enhancing the soil’s load-bearing capacity, while the optimum moisture content decreases from 17% to 10.5%, reflecting reduced water requirements for compaction. These variations highlight the effective stabilization of expansive soil with coal ash and RHA combinations.