Stimulated decomposition in peat for engineering applications

Abstract

Peat deposits are highly compressible, undergoing significant long-term settlement, particularly for fibrous peat. Since decomposition of organic matter can have a significant effect on compression behaviour, the ability to artificially stimulate and pre-decompose a bearing peat stratum prior to the main construction works may mitigate against increased compression rates reported to occur over the design life. This paper presents a feasibility trial of a technique that accelerates the decomposition process in peat prior to entering into full laboratory and field testing. The main decomposition limiting factors of pH and carbon:nitrogen (C:N) ratio are adjusted by adding sufficient amounts of basic and nitrogenous materials. The proposed technique can be tailored for specific peat deposits and can also be achieved in a more sustainable manner. In the trial on moderately decomposed fibrous Sphagnum peat, different peat blends were prepared using additives of peat pulverised fuel ash (PPFA) and urea. Optimum C:N ratio and pH for decomposition were achieved by adding ∼21 kg PPFA and ∼1·5 kg urea per cubic metre of wet peat. The availability of natural decomposers in the peat was also confirmed pre- and post-treatment using a plate count technique, with measured microorganism populations of the order of 105colony-forming units (CFU)/g dry peat.