Consequences of drying on the hydro-mechanical response of fibrous peats upon compression

Abstract

Peats are encountered in waterlogged deltaic areas, where degradation is delayed by favourable environmental conditions. The recent increase in frequency and severity of droughts is expected to accelerate peats degradation, in turn increasing subsidence and flood risk, urging better understanding of the response of peats to drying events. To this aim, compression tests on natural and reconstituted peat samples were performed, supported by X-ray Micro Computer Tomography. The peat fabric is found to be the key factor in the response to drying, with fibres playing the most significant role. Drying in peats starts affecting the macro-fabric, with an irreversible reduction in volume and disruption of the fibrous network occurring under saturated conditions until a threshold void ratio is reached, below which desaturation occurs of the intra-fibres and intra-peds pores. The first drying stage decreases dramatically the compressibility, while the hydraulic conductivity is hardly affected due to enlargement of macropores. Secondary compressibility is affected by the peat fabric besides the organic content. The total organic content does not change substantially over drying, hence, it is not the best proxy to describe the consequences of drying on the response of fibrous peats. The fibre content can be better used to the aim.