During the Holocene, clay has been deposited along the coast and in riverine areas in the Netherlands (Figure 1). These young clays are relatively easy to deform, compared to older deposits that are often more buried. During additional loading, the change in effective stress causes the void space to decline. The gasses and fluids present in the pore space are expelled during this process. Due to the low hydraulic conductivity of clay-rich deposits, the expulsion of fluids and accompanying compaction of the deposits can have a very extended duration. This process is not always reversible, depending on the extent to which the deposit restructures. The void space can also decrease due to increased soil suction, which is induced by evaporation or declining groundwater levels, causing shrinkage of the clay deposits. This process is also partly reversible, but if a soil suction threshold value is exceeded, (part of) the shrinkage is irreversible. In combination with the physical volume change processes, also chemical change of the pore water composition can change the structure of the clayey deposits, changing both volume and compressibility of the deposits. Irreversible volume loss of clay deposits yields land subsidence. As the clay deposits are mostly situated in the low-lying areas of the Netherlands, their permanent compaction would increase the intensity and risk of floods and salt water intrusion. The reversible volume change has also caused a significant amount of damage to infrastructure. Especially during the recent dry summers, indicating the importance of predicting clay shrinkage around infrastructure and in urban areas.
This research focusses on determining the governing soil characteristics with respect to swelling-shrinkage behaviour of clayey deposits and quantifying the irreversible and reversible shrinkage taking place in the deposits, in relation to different physio-chemical conditions. This research project is carried out by Bente Lexmond (UU-GEO), with guidance of dr. Esther Stouthamer, prof. dr. Jasper Griffioen and dr. Gilles Erkens and started in October 2020.
Currently, sample locations are selected for studying the relation between the organic matter content and shrink-swell behaviour of several clay-rich deposits. Several master student projects are set up to study the influence of pore water salinity on shrinkage of fluviatile clays in collaboration with dr. Cjestmir de Boer (TNO).