Mechanical characterisation of new Sand-Hemihydrate rock-analogue material: Implications for modelling of brittle crust processes

Abstract

The analogue materials play a critical role in dynamically scaled experiments, defining the processes that can be simulated and the structures observable in the model. The dynamic scaling enables the direct comparison between the model and its natural counterpart. To obtain such a model the physical and mechanical properties of the analogue material must be scaled with respect to the rock prototype. A large variety of materials have been applied in analogue modelling studies to address the physical and mechanical requirements for the simulation of (i) upper crust, (ii) middle crust and (iii) lower crust and mantle processes. Nevertheless, the development of new model materials represents a continuous improvement of the analogue modelling techniques.We investigated the mechanical and physical properties of a new Granular Rock-Analogue Material (GRAM) (introduced in Massaro et al. (2022)) and its component materials. GRAM is an ultra-weak artificial sandstone composed of quartz sand cemented with gypsum, capable to deform by tensile and shear failure under variable stress conditions. GRAM aggregates in different mixing ratios (from 1% to 4% in weight of hemihydrate powder) were systematically tested with ring-shear tests and uniaxial compression tests. The relationships between the hemihydrate content and the mechanical properties of GRAM were examined. Additionally, the sample preparation procedure of GRAM was investigated, evaluating the impact of the residual water content on the mechanical properties of GRAM aggregates and defining a standard preparation procedure. Finally, GRAM was compared to natural rocks and to other granular materials applied in analogue modelling studies, in terms of physical and mechanical properties, application to physical modelling and dynamic scaling. It was underlined how the application of GRAM aggregates in dynamically scaled experiments can enhance the comprehension of the fault and fracture processes occurring at the scale of the damage zone.