Double pot cover effect in unsaturated soils

The phenomenon of moisture increase under an impervious cover in soils due to thermal gradients is defined as the pot cover effect, which may lead to an obvious soil moisture increase in the shallow soil. This paper explores a measure of laying an impervious layer at an appropriate depth in the process of foundation treatment to eliminate the potential moisture increase in the covered soil. Because the impervious cover above the soil and the impervious layer inside the soil constitute a “double pot cover” structure, the moisture migration in the covered soil with an impervious layer is generalized as the double pot cover effect. To investigate the mechanism of the double pot cover effect and further determine the optimal depth of the impervious layer, a numerical model is established to simulate this problem. Analysis results indicate that the moisture increase under the cover varies with the depth of the impervious layer. As the impervious layer is laid at a certain depth, the moisture increase reaches a minimum value. Moreover, the double pot cover effect under different boundary temperatures is further discussed. Results show that the moisture increase in the covered soil can be significantly reduced by laying the impervious layer slightly below the freezing front (0 °C).