Abstract: Sandstone, a widely distributed sedimentary rock, is extensively used in engineering. It is essential to study the macroscale physical and mechanical properties of sandstone from the microscale. A numerical model is proposed to predict the uniaxial compressive strength and longitudinal wave velocity of sandstone from the mineral crystal scale. First, a microscopic rock mechanics test system, consisting of optical microscope, automatic mineral analyzer, and nanoindentation instrument, is established to obtain the mineral composition, microstructure, and mechanical parameters of the major diagenetic and cementing minerals in sandstone. Then, an accurate grain-based model of the sandstone is developed using the obtained results. The stress evolution in the minerals, and the whole process from the initiation of microcracks in the cementing minerals kaolinite and muscovite to their expansion and then to overall shear failure of the model, can be visually shown through the uniaxial compression simulation. Wave velocity simulation intuitively demonstrates that the propagation characteristics of P-waves in sandstone are primarily influenced by micropores. Results show that the simulated uniaxial compressive strength and longitudinal wave velocity of sandstone are similar to the results of laboratory uniaxial compression test and ultrasonic test, which verifies the feasibility of using microscopic rock mechanics test results to establish an accurate grain-based model for predicting these properties. This method provides a new perspective of cross-scale analysis from mineral crystal scale to macroscopic mechanical properties in sandstone research. It also provides a theoretical basis for sandstone engineering application and interpretation of geological evolution history.

Key words: sandstone, microscale rock mechanics test, accurate grain-based model, uniaxial compressive strength, wave velocity