The diagenesis of welded tuffs is a process in which volcanic debris undergoes degassing, compaction, and quenching, and vitreous rheologic, which indicates that the welding occurred in a high-temperature, high-pressure diagenetic environment and that different temperatures and pressures result in different degrees of welding in the welded tuffs, which can also result in differences in the mechanical properties of the rock. In this study, based on petrographic identification, mineral composition analysis, and pore structure characterization, uniaxial compression combined with linear accelerator CT and Brazilian splitting tests was carried out to investigate the influence of the welding degree on the strength and failure modes. The test results showed that although they had almost similar mineral composition and porosity, the uniaxial compression strength and tensile strength of the strongly welded tuffs were greater than that of the weakly welded tuffs. Their failure modes were also different. Fractures in the weakly welded tuffs developed gradually, while the strongly welded tuffs showed a higher brittleness with sudden failure. The results of this study shed light on the influence of the diagenetic environment on the mechanical properties of rock from a geological perspective and can provide a mechanical basis for rockfall risk evaluation in scenic areas of welded tuff.

Welded tuffs have a wide range of welding degrees and show significant variability in mechanical behavior. However, the detailed influence of welding degree on the meso-mechanical behavior of welded tuffs remains unclear. Based on petrographic and pore-structure analysis, we conducted a series of meso-mechanical experiments on weakly to strongly welded tuffs by utilizing a mesoscale real-time loading-observation-acquisition system. The results indicated that the strongly and weakly welded tuffs showed a small range in mineralogical composition and porosity, while the meso-mechanical behavior exhibited significant variability. Strongly welded tuffs showed lower uniaxial compression strength, weaker mechanical anisotropy, and smaller fracture surface roughness. In contrast, weakly welded tuffs exhibited higher uniaxial compression strength, stronger mechanical anisotropy, and rougher fracture surface roughness. Welded tuffs with strong packing and welding of glass shards tended to have fractures propagating along the maximum principal direction, while those with weak packing and welding of glass shards may have had failure along the alignment of glass shards. The influence of welding degree on the meso-mechanical behavior of welded tuffs probably originates from their diagenesis environments, mainly depending on the combined effect of the pyroclastic properties and pseudo-rhyolitic structure. The findings reveal the meso-mechanical differences of welded tuffs and shed light on improving tuffs for stable and durable construction.