Dependence of macro mechanical behaviour of gypsum on micro-scale grain-size distribution

The exploitation of gypsum by both open pit and underground quarries requires a close evaluation of the mechanical features and variability. However, gypsum rock testing often neglects the natural heterogeneity. The result is an inaccurate mechanical characterisation that averages the strength values of different materials leading to an underestimation or overestimation of the stability conditions, without offering a real representation of the mechanical behaviour of the rock. Grain-size, grain-sorting, mineral composition and porosity significantly influence gypsum mechanical behaviour. The individuation of textural and compositional features that primarily influence the variation in mechanical parameters may offer an interpretation key of the phenomenon. In this study, the relation between the features at the microscale and macro-mechanical behaviour of gypsum rock was analysed with a multiscale approach. Relationships between uniaxial compression strength (UCS), grain-size distribution and porosity were analysed and discussed. Microscopic observations on thin sections were performed, developing an image analysis procedure for correlating textural and structural parameters with UCS.