Experimental investigations to evaluate benefits of using compost amendments to modify expansive soils
Composting is a successful method of recycling organic waste materials such as yard trimmings, municipal biosolids, animal manure and organic urban wastes into stabilised materials that could be used for bioremediation, erosion control, landscaping, and roadside vegetation. The process of organic wastes composting is expanding rapidly in the USA and other countries since landfill spaces for disposal of organic wastes are becoming scarce and expensive. Researchers and practitioners always seek new application areas for composts. Compost materials, given their moisture affinity (hydrophilic characteristics) and low permeability characteristics, could provide stabilisation of natural expansive subgrades by mitigating shrinkage cracking and encapsulating subsoil surfaces. In order to verify these advantages, a research study was conducted to measure geotechnical characteristics of composts and Compost-Treated Topsoils (CMTs). Two types of composts, dairy manure and biosolids, and a local expansive soil were studied. This paper presents the laboratory test results, which showed that compost amendments resulted in the reductions of linear shrinkage strains and increase of shear strength and swell strains. Ranking analyses of test results also showed that compost amendments provided low to moderate enhancements to subsoil properties. Currently, field studies are being conducted to address potential applications of CMTs as unpaved shoulder covers to encapsulate and maintain compaction moisture conditions.
Keywords: expansive subgrades, volumetric changes, longitudinal cracking, transverse cracking, stabilisation, organic waste materials, dairy manure compost, biosolids compost, composting, compost amended soils, waste management, environmental management, recycling, reuse, geotechnical engineering, topsoil, bioremediation, erosion control, landscaping, roadside vegetation