Experimental investigation and numerical simulation of wetting-induced volume changes of sandy soils from lignite opencast mining dumps

This study investigates the wetting-induced volume change (collapse) behaviour of two sandy soils originating from a lignite opencast mining dump. The influence of varying boundary conditions, including applied vertical stress, initial degree of saturation, initial density, and scale effects, on the wetting- induced collapse is analysed based on one-dimensional collapse tests. The influence of scale is examined through oedometer and column tests on samples of different sizes. The hydraulic properties of the materials are evaluated using soil-water retention curve (SWRC) tests, employing hanging column and axis-translation techniques. The results indicate that initial density has the most significant impact on wetting-induced volume changes, while the initial degree of saturation is of secondary importance and the effects of vertical stress and scale are rather small. The coupled hydromechanical model proposed by Tafili & Machaček [1] is used to simulate the wetting-induced collapse behaviour. For this, the model is linked with two different hydraulic models for the SWRC, which do or do not consider volume change during hydraulic loading. Simulations demonstrate the capability of the coupled model to accurately replicate the experimental observations, irrespective of the choice of the hydraulic model.