## 3 Results and Discussion
### Experimental Results of Single-Crack Specimens with Different Angles
#### 3.1.1 Fixed Angle  
The 70-degree crack model was chosen as an example to analyze the experimental results, in order to explore the influences of axial pressure and confining pressure on the microscopic and macroscopic joint seepage and the seepage channels. The joint hydraulic aperture and seepage channel were analyzed in detail under two kinds of stress boundary conditions: (1) axial stress 5 MPa, confining pressure 30-5 MPa and (2) confining pressure 5 MPa, axial stress 45-0 MPa. (1) An axial pressure of 5 MPa was applied to the upper boundary of the model. The confining pressure was 30 MPa to 5 MPa. The pressure difference between the upper and lower ends was \(\Delta\)p = p2 - p1 = 2 MPa. The hydraulic aperture of the joints is shown in Figure 15. The joint flow and the main seepage channel are shown in Figure 16.  
When the confining compressive stress level is at 30 MPa or 25 MPa, almost all vertical joints and a large number of inclined joints reach the residual value. The closure of the vertical joint directly leads to a large number of closures in the vertical seepage channel. At this time, the microscopic seepage channel is mainly composed of a large number of horizontal joints and a small number of inclined joints. At 30 MPa, the macroscopic joint aperture values were mainly 1.78 \(\times\) 10\({}^{-5}\), while at 25 MPa, the macrojoint aperture values were mainly 1.78 \(\times\) 10\({}^{-5}\) and 2.0 \(\times\) 10\({}^{-5}\). When the confining pressure was lowered to 20 MPa or 15 MPa, almost all vertical joints and a few inclined joints reached the residual value. The closure of the vertical joint directly led to a large number of closures in the vertical seepage channel. The microscopic seepage channel was mainly composed of a large number of  
Figure 14: Seepage results with different crack angles. horizontal joints and inclined joints. At 20 and 15 MPa, the macrojoint aperture values were mainly \(2.0\times 10^{-5}\). When the confining pressure reduced to 10 MPa or 5 MPa, only the local vertical joints reached the residual value. The network structure, consisting of vertical joints, inclined joints, and horizontal joints, contributed to the formation of seepage channels. The macrojoint openings at 10 MPa and 5 MPa were mainly \(2.23\times 10^{-5}\). In the process of reducing the confining pressure, the large influence of the confining pressure on the microscopic vertical joints will lead to a large change in the vertical microscopic seepage channel. The increase in the joint aperture value of the macroscopic crack causes an increase in the seepage flow rate so that the main seepage channel is composed of macroscopic cracks, as shown in Figure 16.  
(2) A 5 MPa confining pressure was applied to the boundary of both sides of the model. The axial pressure was 45 MPa to 0 MPa. The difference in pressure between the upper and ends was \(\Delta\)p = p2 - p1 = 2 MPa. The hydraulic aperture values of the joints are shown in Figure 17. The main seepage channels of the joints were the same as those shown in Figure 16, except for the presence of a slightly different joint flow rate, which is not described here. When the axial stress level was greater than 35 MPa, almost all of the horizontal joints and a large number of the inclined joints reached the residual value. Closure of a horizontal joint directly led to a large number of closures in the horizontal seepage channel. At this time, the microscopic seepage channel was mainly composed of a large number of vertical joints and a small number of inclined joints. The macrojoint aperture values were mainly \(1.78\times 10^{-5}\), \(2.0\times 10^{-5}\), and \(2.23\times 10^{-5}\). When the axial stress reduced to the 25-15 MPa stress interval, almost all of the horizontal joints and a small number of inclined joints reached the residual value. The closure of the horizontal joint also directly led to a large number of closures in the horizontal seepage channel. The macrojoint aperture values were mainly \(2.0\times 10^{-5}\) and \(2.23\times 10^{-5}\).