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 105 colony-forming units (CFU)/g dry peat.