Pore property as an indicator of macro-deterioration in slightly weathered tuffs

Abstract Tuff rock is highly heterogeneous due to volcanic activity, hydrothermal alteration, and weathering. It is difficult to explain the deterioration mechanisms of the weathered rocks merely based on mineralogical and chemical parameters. It has been reported that subtle weathering can modify pore structure and subsequently affect the rock mechanical behavior of tuffs. In this work, the pore characteristics in slightly weathered tuffs and fresh tuffs are systematically analyzed based on Nuclear Magnetic Resonance (NMR) and Mercury Intrusion Porosimetry (MIP) tests. Additionally, meso-level uniaxial compression tests were conducted on the tuff samples by utilizing the MTI–LM (miniature tensile instrument–light microscope) system to detect the crack propagation and deformation process. The results demonstrated that additional mesopore (10–50 nm) increases with pore throat expansion during weathering, and the change of pore structure influences the tuff failure mode. Specifically, for the slightly weathered tuff, crack initiates in the altered minerals or matrix and results in shear failure. However, as for the fresh tuff, crack usually initiates in the intact and fresh minerals and matrix, and eventually leads to tensile failure. Therefore, we propose that tuff pore property can serve as potential indicator of the micro-mechanism of substantial macro-deterioration due to weathering.