Abstract: The variation of the disintegration characteristics of red-layer soft rock with changes in water content has significant engineering importance. To accurately describe the disintegration characteristics, it is necessary to propose appropriate disintegration indices. Currently, widely used disintegration tests under drying-wetting cycles cannot measure the continuous process of disintegration rate as water content changes. Commonly used disintegration indices, disintegration resistance index Id and disintegration rate DR, are unable to accurately measure the degree of disintegration or distinguish differences in disintegration characteristics. To address this issue, a method for calculating the surface area of granular materials was derived. A new disintegration index, the disintegration surface release rate (DS), was proposed, and the differences between various disintegration indices were compared. Water immersion and disintegration tests were conducted to study the impact of the number of drying-wetting cycles on D_S. Discrete element method (DEM) simulations were performed to study the impact of moisture content on D_S. The results show that DS has an accurate physical meaning and accurately describing the influence of particle size on the disintegration rate. With the increase in the number of cycles, the DS change rate reaches its maximum after the second drying-wetting cycle, and DS tends to stabilize after the fifth disintegration cycle. As disintegration time (t) increases, D_S exhibits a nonlinear change, initially increasing and then stabilizing. D_S shows a linear relationship with saturation (Sr). This research is of great significance for the engineering application and disintegration prediction of red-layer soft rock.

Key words: red-layer soft rock, disintegration characteristics, disintegration indices, discrete element simulation