Evaporation-induced soil water flux to design suction drain for low-carbon ground stabilisation: experimental investigation and modelling

The suction drain is a novel concept for low-carbon temporary ground stabilisation in clayey soils alternative to jet grouting and ground freezing. Boreholes are drilled into the ground and air is injected to the borehole end through a delivery pipe. The air flowing through the gap between the pipe and the borehole surface backward towards the borehole entry removes water by evaporation and, hence, increases the undrained shear strength of the soil surrounding the drain. There are no studies that allow quantifying soil water evaporation generated by tangential airflow for the case of ‘wind tunnel’ only a few centimetres high over an evaporating surface a few meters long. This paper first presents an experimental investigation on water evaporation induced by air flow. A 3m long wet surface was subjected to tangential air flow into a 40mm gap. Tests were carried out by considering different air velocities and inlet air relative humidity. A model was then formulated to quantify the water evaporation rate for any length of the wet surface. The model parameters were calibrated against one experimental dataset and the model was then validated against an independent dataset. Finally, an empirical equation is proposed to estimate model parameters without the need of carrying out experimental tests. This is based on the vapour transfer coefficient established empirically for evaporation from open water (external air flow), which was found to remain valid for confined evaporation (internal air flow). The paper therefore provides a tool to estimate airflow-induced evaporation to successfully design the suction drains.