Research on the characteristics of re-crushing and void evolution laws of rock blocks under water-rich conditions

The re-crushing behavior of rock blocks under water-rich conditions is key to ground stability and the diffusion characteristics of grouting filling slurry. Yet quantitative evolution of the void structure between rock blocks and quantitative study of the coupling mechanism among moisture, load, and particle re-crushing remain insufficient. This study conducted a systematic laboratory simulation under water-rich conditions, investigating re-crushing and void structure evolution across three moisture levels (natural: 4.7%, semi-saturated: 6.3%, saturated: 7.9%) and five axial load levels (70-350 kN). A layered filling and graded loading path was adopted. The results show that the compaction strain-load curve exhibits a clear two-stage characteristic: a rapid compaction stage dominated by pore compaction, followed by a slow compaction stage accompanied by particle re-crushing; as the moisture content and load increase, the compaction strain becomes more obvious, with over 90% of the total deformation occurring in the initial rapid compaction stage. Higher moisture content continuously reduces the incremental strain of each loading step, and particle re-crushing is most significant in the 20-25 mm particle size range, transforming the initial normal particle size distribution into an exponential distribution after compaction. The compaction degree and total crushing value show a power-law relationship with the external load. The compaction degree and total crushing value exhibit a strong linear correlation (R 2 > 0.98) under all moisture conditions. The initial voids are large and unevenly distributed. Before re-crushing, moisture slightly homogenizes the pore structure. In contrast, after compaction, large pores decrease sharply, narrow pores increase, and the pore space distribution becomes more uniform - high loads and high moisture content both amplify this effect. Quantitative image analysis confirms that the equivalent diameter of rock blocks and the equivalent diameter of voids both follow a log-normal distribution, and their shape and dispersion are jointly influenced by load and moisture. The research results provide a basis for understanding the re-crushing characteristics and long-term subsidence of water-rich mined-out areas, and offer practical guidance for risk assessment and backfill design of mined-out areas.