## 5 Conclusions  
This study proposed an impact-induced strength corrosion calculation model and then incorporated it into the discrete element numerical simulation of broken rock mass subjected to confined compression and water immersion conditions. The deformation and fracture characteristics, as well as the AE features of broken rock mass with different size grading distributions considering impact-induced strength weakening, were investigated, and the evolution laws of layer-by-layer porosity and average porosity in the broken rock mass were analyzed. The main research findings are as follows:  
Figure 13: Evolution curve of average porosity of broken rock mass under compressive load and water immersion.  
(1) The stress-strain curve of confined compressed and water-immersed broken rock mass exhibits an exponential growth pattern, which can be divided into three stages: the initial stage, the slow growth stage, and the rapid growth stage. When the proportion of large-sized rock blocks in a broken rock mass is high (size grading as G5), the stress-strain curve exhibits the highest growth rate. Conversely, when the grading size distribution is classified as G4, which signifies a higher proportion of smaller particles and a relatively larger void ratio after compression, the stress-strain curve exhibits the slowest growth rate. When there is a significant difference in particle sizes (graded as G3), it results in a more stable skeleton structure and, thus, a slower growth rate in the stress-strain curve.  
(2) The increase in AE events in broken rock mass samples considering impact-induced strength erosion is significantly higher than the case without considering this erosion during the early loading stage. However, there is little difference between them during the later loading stage. When the particle size of the broken rock mass is significantly different (graded as G3), impact strength erosion has the greatest impact on the growth of microcracks and the breakage rate in the broken rock mass. Conversely, when the particle size of the broken rock mass is uniform (graded as G1), impact strength erosion has minimal influence on secondary fracturing in the broken rock mass. The deformation and fracture of confined compressed and water-immersed broken rock mass are primarily controlled by the evolution of pore structure in the initial stage, impact-induced strength erosion in the slow growth stage, and interlocking between rock blocks in the rapid growth stage.  
(3) When the strain of the broken rock mass is less than 0.175, the microcracks are scattered. When the strain reaches 0.275, microcrack propagation accelerates and forms a clustered distribution. At a strain of 0.375, microcracks exhibit a mesh-like pattern with enhanced connectivity. With the continuation of deformation, the porosity curve fluctuates along the z-axis with a decreasing trend and gradually becomes more uniform. When the strain reaches 0.275 and 0.375, significant symmetrical fluctuations in the broken rock mass porosity curve are observed at both ends of the sample. When the size grading distribution is classified as G4, the broken rock mass shows the lowest porosity, and the highest when classified as G5.  
Conceptualization, F.M.; Methodology, F.M. and Y.C.; Software, W.L. and Y.C.; Resources, H.P.; Data curation, M.L.; Writing--original draft, W.L.; Writing--review & editing, F.M.; Supervision, H.P. and M.L. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Fundamental Research Funds for the Central Universities (2022 QN1024).  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflict of interest.