Abstract:

To investigate the relationship between the macro-micro structure of sandstones and their mechanical properties, energy evolution characteristics, and failure modes during cyclic loading, the meso-scale observations and cyclic loading/unloading tests were conducted on siltstone and coarse sandstone to analyze the microscopic structure, stress-strain characteristics, energy evolution characteristics, and failure modes of these two types of sandstones. The results indicate that siltstone exhibits smaller grain sizes, denser structures, larger contact areas between microscopic components, and stronger cementation than coarse sandstone, resulting in a 22.15% increase in uniaxial compressive strength. The hysteresis loop migration is less pronounced in siltstone as the number of cycles increases, whereas in coarse sandstone, the hysteresis loop shifts towards increasing strain. As the peak stress rises, the energy per unit volume of the siltstone follows a quadratic function trend, while the elastic energy per unit volume increases linearly. In contrast, both the energy per unit volume and the elastic energy per unit volume of coarse sandstone show a linearly increasing trend. The dissipative energy per unit volume for both siltstone and coarse sandstone shows a quadratic function trend, initially decreasing and then increasing. The failure mode of siltstone is characterized by tensile failure, resulting in poor specimen integrity after failure. In turn, coarse sandstones fail via a single inclined plane shear failure, causing the specimen to split along the plane of the shear failure after failure, maintaining better structural integrity.

Key words: siltstone, coarse sandstone, hysteresis loop, energy evolution, failure mode