## 5 Discussion
### Influence of Block Size on the Key Shear Zone Thickness  
At a stone content of 30%, the block stones were suspended in the sample, and the shear deformation was mainly characterized by horizontal slipping. The thickness of the key shear zone was smaller, and the impact of the block size on the shear zone thickness was not obvious (Figure 18). For a sample with the same stone content, as the size of the block stone increased, the number of blocks decreased (Figure 19). The thickness of the shear zone was directly affected by the spatial distribution of block stones in the sample. The thickness of the shear zone of sample with stone content of 30% varied from 4 to 6 cm. At a stone content of 50%, the variation in the thickness of the key shear zone of the SRM with different particle sizes was decreased. The thickness of the shear zone of sample with stone content of 50% varied from 5 to 7 cm. Under the condition of a high stone content (70%), the thickness of the key shear zone increased with the block size increasing. The thickness of the shear zone of sample with stone content of 70% varied from 5 to 8 cm. The main reason for this was that the large stones near the fracture plane would roll or swell with slippage of the shear plane, resulting in an increase of the range of the key shear zone. On one hand, there was a larger \"gear effect\" caused by the rolling of large stones penetrating the shear plane. On the other hand, the large stones on both sides of the shear plane climbed along the contact surface to produce a shear dilatancy effect.  
The essential reason for the influence of the stone content and block size on the key shear zone thickness was the tightness degree of the block stone arrangement. With the stone content increasing, the \"gear effect\" among the block stones was enhanced, and the coarse particles squeezing each other gradually took the stress. The probability of the stones embedded with each other decreased with block size in samples increasing under the same stone content. The samples exhibited the characteristics of the concentrated distribution for large stones and dispersed distribution for small stones (Figure 19). Thus, the disorder degree of the block stones in SRM decreased with block size increasing under the same stone content.  
Figure 17: Deformation characteristics of block stones throughout the shear plane. (**a**) Single row of stones throughout shear plane, (**b**) location of these stones after shearing, (**c**) vertical view of the stones after shearing, (**d**) double row of stones throughout the shear plane, (**e**) location of these stones after shearing, (**f**) vertical view of the stones after shearing.  
Figure 19: Schematic drawing of the block stone size and distribution. (**a**) A state in which the strength is completely controlled by the soil; (**b**) a state in which the strength is mainly controlled by the soil; (**c**) a state in which the strength is controlled by the soil and stone; (**d**) a state in which the strength controlled by the stone.  
Figure 18: Variation in the key shear zone thickness with increasing stone sizes under different vertical pressures. (**a**) 50; (**b**) 200; (**c**) 300; (**d**) 400 kPa.