## 2 Experimental Investigation of Structural Evolution of Rock Specimens
### Experimental Results
As shown in Figure 4a, before position A, the global mechanical behavior is in the elastic stage. The deformation localization is not significant during the elastic deformation stage, and the accumulative AE ringing counts, variance S and dislocation displacement increase slowly. After position A, the global mechanical behavior of the rock specimen exhibits non-linear evolution. To show the evolution characteristics of different indexes in the non-linear stage clearly, the region of the red dashed line in Figure 4a is magnified and shown in Figure 4b. The \(\mu\epsilon\) in the x-axis of Figure 4a,b is micro-strain. Figure 4b shows that from position A to position B (the peak stress point) the increase in accumulative AE ringing counts is almost constant. However, the curve of variance S changes direction rapidly and the dislocation displacement increases at a faster rate, reflecting the additional enhancement of deformation localization. The dominant DLB forms at position B. The dominant DLB is the result of micro-crack propagation and connectivity. Therefore, the dominant DLB is equivalent to the \"weak interlayer structure\" in the rock specimen. It is worth emphasizing that position B marks a turning point at which the dislocation displacement curve changes direction. This phenomenon indicates that  
Figure 4: Curves for different parameters: (**a**) Whole process loading; (**b**) non-linear stage. Figure 3: Principle of dislocation displacement calculation: (**a**) Layout of measuring points; (**b**) decomposition of displacement. the mechanical property of the rock specimen has changed dramatically at position B. After position B, the medium of the rock specimen becomes discontinuous. Next, the sharp increase in the accumulative AE ringing counts indicates that the macro-crack in the rock specimen has expanded, leading to the final failure of the specimen. The evolution characteristics of deformation field are uniform to non-uniform and continuous to non-continuous. These characteristics can be reflected by different indicators. Thus, the deformation state of rock can be divided according to the change of different indicators. The whole deformation process of the rock specimen can be qualitatively described as follows. First, in the early loading stage, the global mechanical behavior shows linear evolution characteristics, and the deformation field is relatively uniform. The dislocation displacement, variance S and accumulation of AE ringing counts increase slowly. Second, as the loading increases, the presence of non-linear change of variance S indicates that the deformation field becomes non-uniform, and the DLB (weak interlayer with control effect) appears gradually, and the deformation changes to \"structural control\". The exhibited global mechanical behavior is non-linear. The peak point is a key turning point of rock mechanical behavior. The turning point of the relative dislocation displacement curve indicates that the rock specimen becomes non-continuous from continuous. Before this point, the loading is carried by the whole specimen and can be increased constantly. However, after the peak point, the load-bearing of the specimen decreases gradually. Finally, the load-bearing capacity reduces rapidly because of the growth of the macro-crack within the dominant DLB, and the dislocation displacement, variance S and accumulation of AE ringing counts changed rapidly. According to the analysis of the experimental results, when there is a weak interlayer with a control effect in the rock specimen, the global mechanical behavior of rock shows a strong structural control characteristic. The influences on global mechanical behavior evolution can be described as follows: after the structure with the control effect formed, the bearing mode and bearing capacity of the rock were changed. The intact rock, that is, the rock specimen at the initial stage of loading, is a whole specimen to bear external load, and the bearing capacity is strong.