Influence of size on the compressive strength of tuff under different dry and wet conditions

This paper addresses the issue of tuff strength degradation under repeated rainfall. Cylindrical specimens with varying diameters (30–70 mm) and different numbers of wet-dry cycles (0–21 times) were used for uniaxial compression tests. A coupled “size-cycle number” model was established through regression analysis. The results indicate that the uniaxial compressive strength of tuff decreases exponentially as the size increases; the more the number of wetting-drying cycles, the more pronounced the strength reduction becomes. Based on the size effect model, the characteristic size decreased from 894.63 mm to 232.60 mm, and the corresponding characteristic strength decreased from 74.55 MPa to 21.52 MPa, both exhibiting a significant exponential decay pattern. The fluctuation coefficient and normalized curve further indicate that as the sample size increases, the strength dispersion decreases, and the size effect gradually weakens. This study quantifies the variation characteristics of size effect of tuff under wetting-drying cycles and proposes a strength prediction model and key parameters. These can be used for slope strength attenuation assessment, critical size determination, and instability risk warning during rainfall processes, providing a direct quantitative basis for related rock engineering. Revealed the overall impact of repeated wetting-drying cycles on the strength evolution of tuff. Multiple wetting-drying cycles can weaken the influence of size on rock strength. The study provides a reference basis for evaluating the stability of reservoir slopes in wet environments.