## 6 Conclusions  
In this analysis, the effect of RFCA on the mechanical properties of similar materials simulating weak rock mass was analysed by UCTs. The influence rule of RFCA on the contact force and failure evolution of the similar materials from a mesoscopic perspective by discrete element analysis was discussed. The following conclusions were obtained:  
1. Based on the results of discrete element analysis, nonlinear fitting equations of the elastic modulus correlating with the fine aggregate percentage and confining stress were proposed. The nonlinear fitting equations of the friction angle and cohesion correlating to the fine aggregate percentage were presented. This provides a method for evaluating the strength and deformation parameters by the aggregate percentage for similar materials. 2. Different RFCAs significantly affect the stress-strain curves of similar materials under compression. As the fine aggregate percentage decreases, the stress-strain curve reaches the pre-peak yielding stage at an earlier point, and the post-peak softening stage is more ductile. Conversely, as the fine aggregate percentage increases, the specimens become more resistant to yielding, and the post-peak softening stage is more brittle. 3. With the increase in RFCA, the internal friction angle presents a trend of initial decreasing and then increasing. When the proportion of fine aggregate is less than or equal to 0.2, the internal friction angle, regulated by occlusal friction, is predominantly controlled by the skeleton between coarse particles. With the proportion of fine aggregate increases, the skeleton effect between particles becomes weak, and the friction decreases. When the proportion of fine aggregate is over 0.2, the method of friction transforms from occlusal friction to sliding friction. As the number of fine aggregate particles significantly keeps augmenting due to the increase in the proportion of fine aggregate, the sliding friction subsequently increases, resulting in the growth of the internal friction angle. 4. When the proportion of fine aggregate is low, the propagation of microcracks between fine aggregates is easily hindered by the presence of coarse aggregates. Furthermore, the microcracks expand around the edge of the coarse aggregate, and the direction of the crack growth will change with the rotation around the edge of the coarse aggregate, making it more conducive to form macroscopic shear cracks. When the proportion of fine aggregate is high, the microcrack propagation between fine aggregate is slightly influenced by coarse aggregate, which tends to expand vertically along the edge of fine aggregate, ultimately forming vertical macroscopic cracks. The simulated macroscopic crack patterns and angles are similar to those captured from the results of laboratory tests. (5) The results of this study provide valuable insights into the effects of RFCA on the mechanical properties of similar materials. However, the limited number of samples tested suggests that these findings should be treated as preliminary. Future work should focus on expanding the dataset through additional experiments to validate and refine the relationships established here. (6) The findings of this research on the mechanical properties of similar materials simulating weak surrounding rocks provide a robust scientific basis for enhancing geotechnical engineering practices. By identifying the optimal ratio of fine-to-coarse aggregate (RFCA) and its impact on key mechanical properties such as elastic modulus, cohesion, and internal friction angle, this study offers valuable insights for the design of more accurate and reliable geotechnical models. These findings can be applied to optimise the design of model tests, thereby reducing the need for extensive experimental trials and saving significant time and resources.