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 10 5 colony-forming units (CFU)/g dry peat.

Effects of decomposition on the compressibility of fibrous peat — A review

“…Pichan and O'Kelly (2013) reported mean microorganism counts of the order of 10 5 colony-forming units (CFU)/g for moderately decomposed Sphagnum peat (dry mass basis); consistent with the value of ~2.6 x10 5 CFU/g reported by Hunter et al (2006). However large variations in microorganism populations in mire naturally occur with depth (Barns and Nierzwicki-Bauer, 1997).…”

Drying temperature and water content–strength correlations

“…It can also be argued that the LL and PL conditions are defined for fine-grained mineral soils, with specific physical meaning, and that these Atterberg limits should not be applied to organic soils (O'Kelly, 2014). For fibrous materials including sewage sludge and fibrous peat, it is often not possible to perform the PL test, in that uniform soil threads cannot be rolled out to 3 mm in diameter on account of scale effects related to the coarse fibrous particles and hence these materials are reported as non-plastic (O'Kelly and Zhang, 2013;Pichan and O'Kelly, 2013;Zhang and O'Kelly, 2014). However, in practice, the bulk materials are readily remoulded over a certain range of water content and therefore they are plastic.…”

Water Content Determinations for Peat and Other Organic Soils Using the Oven-Drying Method

“…According to the modified von Post peat classification system, [25] the Ballydermot peat deposit was classified as SCWPh-H 4-7 -B 3-4 -F 2 -R 2 -W 1 , the Clara peat material as SCN-H 4 -B 3 -F 3 (S)-R 1 (N)-W 1 (N), and the Derrybrien peat material as CErPh-H 3-4 -B 4 -F(Er) 2 -R(CPh) 3 -W 1. Full descriptions of these peat deposits and their geotechnical properties have been reported for the Ballydermot site by Pichan and O'Kelly [26,27] and O'Kelly and Pichan, [23] for the Clara site by O'Kelly and Zhang [28] and Zhang and O'Kelly, [29,30] and for the Derrybrien site by AGEC. [31] Refined Clara peat material (denoted by Cr) was also prepared for oven-drying tests by blending some of the remolded peat material using an electric handheld blender.…”

“…Note the PL condition could not be achieved for the Ballydermot and Clara peats, in that uniform soil threads could not be rolled out to 3-mm in diameter without crumbling/breaking on account of scale effects related to the fibrous particles. [27][28][29] Hence these materials were reported as non-plastic. In practice, however, the wet peats are readily remolded and therefore plastic.…”