Strength changes associated with water transport in unsaturated tuff during drying

The impact of water content on the strength of sedimentary rocks is a critical area of research, particularly in the contexts of disaster prevention and the construction of underground structures. Despite numerous factors being identified as contributors to the strength variations in sedimentary rocks caused by water content, a comprehensive understanding remains elusive. Moreover, only a limited number of cases have been discussed on strength changes in these rocks during water transport processes. In this study, one-dimensional water transport experiments were conducted during the drying process on Neogene tuff samples from Japan. The experiments focused on the unsaturated permeation of the porous media and analyzed the variations in advection and diffusion terms relative to saturation changes at multiple points. During the drying process, water transfer occurred primarily through diffusion, although advection was significant in the early stages to equilibrate the hydraulic head at the center of the specimen. Furthermore, the same tuff samples, with adjusted water content during the drying process, were tested using Brazilian and uniaxial compression methods to examine the variations in strength properties owing to the variations in water content. By comparing these results with the water transport data, we observed that significant alterations in strength occurred after the convergence of the advection term. It was shown for the first time that the decrease in strength of tuff occurs only during the water diffusion phase. These results are expected to be applied to more accurate evaluation of rock mass stability and advanced numerical analysis. •One-dimensional water transport and strength tests for unsaturated tuff during drying.•Both diffusion and advection terms occur in water transport in tuff.•Advection terms of water transport occur to balance the positional hydraulic head.•Dramatic change in tuff strength only during diffusion confirmed for the first time.•These results contribute to more accurate evaluation of rock mass stability.