Cyclic wetting and drying behaviour of coal wash treated black soil

The abundance of granular waste materials coupled with their successful reuse in construction fills has provided sustainable alternatives to a rather expensive quarried natural rock aggregate. This study focuses on the application of coal wash (CW) as an admixture to mitigate the undesirable shrink and swell characteristics of expansive black soils under unconfined compression loading. CW is a by-product of the coal industry that requires an enormous area of landfill for storage. These landfills pose a serious environmental problem because coal is still being produced in many parts of the world. A series of unconfined compression tests were conducted on CW-soil mixtures with and without wet and dry cycles; these wet and dry cycles mimic the shrink and swell characteristics of expansive soil observed in the field. Our findings show that cracking and shrinking impact the fabric of CW-soil over time, which reduces their shear strength. The incorporation of CW into black soil reduces its susceptibility to shrinkage and swelling during wet and dry cycles. The relationship between the shear strength reduction after repeated wetting and drying are proposed for consideration in the design. The study shows that the addition of CW can improve the geotechnical properties of expansive soils under unconfined compression and curtail the degradation of the areas used to store the CW.