Rehabilitation following open-cast mining aims to build a long-term functional and sustainable soil cover for a stable landscape development. The objective of this study was to assess changes in soil recovery of rehabilitation performed at different times (1980, 1998, 2009, 2016, 2017) measured as soil hydraulic and mechanical properties (shear stress) at an open-cast Yallourn mine site in south-east Australia (Victoria) in 2021. Soil hydraulic properties (SHP) were determined using the extended evaporation method and the water retention and hydraulic conductivity curves were fitted using the van Genuchten-Mualem model. The vane shear tests were performed at two depths (0-8 and 10-18 cm) combined with soil water content measurements. The results of the SHP showed a shift in the soil water retention curve when comparing 1980 and 2017 sites. While the saturated water content i.e., total porosity was the same, the saturated hydraulic conductivity (Ks) decreased from 36.7 to 1.02 cm day-1, respectively. This was mostly connected to the textural pore size distribution, as large differences in clay and sand content among the sites were observed. The vane shear test showed also large differences with rehabilitated sites indicating a larger variation compared to the reference site (exception 2016 site) and having generally higher shear resistances. The observed small-scale heterogeneity of the rehabilitated soils is most likely explained by soil heterogeneity and disturbance due to excavation activities and rehabilitation as well as availability of uniform soil material. Inevitable heterogeneity of the soil hydraulic and mechanical properties should be taken into consideration during the design and construction of various landforms as well as when implementing soil monitoring schemes.
