Bio-stabilisation of soft soil using cattle manure

Environmentally friendly materials are being explored as alternatives to lime and cement binders in ground improvement. Biological treatment methods are environmentally friendly as they rely on the natural activity of ubiquitous microbes to produce extracellular polymeric saccharides (EPS) and calcite cements. EPS extruded by microbes exhibit strong adhesion from growth of fibrous bridges and bonds between surfaces. In situ polysaccharide secretion in soils to improve their engineering properties has not been examined. In this study, pulverised dried cattle manure (CM) are is used for in situ EPS production in a synthetic soft soil specimen. The indigenous facultative anaerobes and aerobes in animal waste produce negatively charged EPS molecules in the soil specimen. Bridging of sand particles and embedment of CM fibres in kaolinite aggregates caused an immediate increase in unconfined compressive strength (UCS) of the stabilised specimen. EPS cementation improved soil strength by filling pores and engulfing kaolinite aggregates into bonded mass. Fibre reinforcement and bio-stabilisation by CM increased the UCS of the soil by 740%. Replacing C-intensive lime/cement binders by CM as a stabilising agent has the potential to prevent release of 1 t of carbon dioxide to the atmosphere per tonne of lime/cement consumed.