Gas exsolution and gas invasion in peat

Abstract

Increasing climatic stresses accelerate the degradation of highly organic soils, like peat, by increasing their drying rate above the water table and their decomposition rate under water. Recent experimental studies provide evidence of the consequences of these processes on the hydro-mechanical properties of peat. However, modelling the experimental evidence in a comprehensive framework remains challenging, especially in the case of anaerobic degradation, which is accompanied by gas generation, exsolution and expansion, into an initially saturated matrix of soil. In this research study, experimental results from undrained isotropic unloading on artificially gas-charged peat samples are combined with data from drying tests on the same peat, in an attempt to develop a unified framework encompassing the two desaturation processes. As a first approximation, simple compression laws depending on the average stress acting on the soil skeleton are used to simulate the experimental results. The comparison between experimental data and model simulations suggests the possibility of modelling gas expansion similar to the gas invasion process occurring on drying. The modelling approach, stemming from unsaturated soil mechanics, is meant to offer a possible framework to include the hydro-mechanical consequences of the effects of degradation of peats in the engineering analysis.