Effects of Wetting and Drying Cycles on Strength of Latrobe Valley Brown Coal

Water penetration, changes in the groundwater level and moisture content changes can affect the physical and chemical properties of coal in an open pit mine. Water levels in open coal pit mines can vary throughout the year, resulting in a number of wet and dry cycles for brown coal. Wet and dry cycles occurring throughout the year can affect the mechanical strength of the stone's microstructure and macroscopic structure. Loss of strength can have severe negative impacts if such rock is integral component in landform design. Until now, no research has been conducted on the effects of wet and dry loading cycles on brown coal. This study investigates the effect of wet and dry cycles on brown coal's strength by conducting a series of unconfined compressive strength (UCS) laboratory tests. For this purpose, nine laboratory samples with dimensions of 38 x 76 cm were prepared. Samples were placed inside distilled water chambers in a temperature-controlled environment. Afterwards, the samples were subjected to unconfined compressive strength (UCS) tests following 0, and 3 cycles of wet and dry conditions. The results of the UCS test show that as the number of wetting and drying cycles increased, the UCS of the samples decreased from 2150 to 330 kPa after three cycles of wetting and drying. In addition, the results indicate that the elastic modulus of brown coal has decreased from 10500 to 1200 kPa. Also, the Poisson ratio decreased from 0.34 to 0.27. This study confirms the importance of paying attention to the wet and dry cycles in brown coal mines.