## 4 Conclusions  
(1) On the basis of crack reconstruction technology involving the typical experimental failure form, this paper presented a new method for hydraulic parameter fitting. The joint hydraulic aperture values of microcracks in rock samples under zero stress were obtained by scanning electron microscopy. The hydraulic parameters of macroscopic cracks were obtained by fitting the results of a triaxial seepage experiment and a numerical simulation. It was found that under the fitting experiment condition, when K (the ratio of the macroscopic crack aperture value to the microscopic joint hydraulic aperture value) <3, changes in the K value had little influence on the joint seepage flow. When K was greater than or equal to 3, there was a quartic polynomial relationship between the flow rate and the K value. (2) The seepage channel of the model is composed of microscopic cracks and macroscopic cracks. With a decrease in the confining pressure, a large number of vertical microscopic joints change from closed to open. With a decrease in the axial pressure, a large number of horizontal microscopic joints change from closed to open. The horizontal hydraulic aperture was shown to be more sensitive to axial stress than the vertical hydraulic aperture, and the vertical hydraulic aperture was shown to be more sensitive to confining stress than the horizontal hydraulic aperture. The network structure formed under conditions of low stress aids in the formation of the microscopic seepage channel. The main seepage channel in the model is composed of macroscopic cracks. The hydraulic aperture of the macroscopic cracks gradually increases as the level of stress decreases. (3) For the single crack model with different angles, as the crack angle increases, under the same stress conditions, the seepage flow rate increases continuously, and the seepage flow rate has a cliff-like increase when the crack angle changes from 60 to 70 degrees. As the confining pressure decreases, the increment of the seepage flow rate increases continuously. The sensitivity of the 70-90-degree cracks to the confining pressure is greater than that of the 40-60-degree cracks. With a decrease in axial pressure, the increment of the seepage flow rate increases continuously. The sensitivity of the 40-60-degree cracks to the axial pressure is greater than that of the 70-90-degree cracks. As the axial pressure decreases, the seepage flow increment for the 40-60-degree cracks increases, while that of the 70-90-degree cracks decreases. The sensitivity of the crack to axial stress first increases and then decreases. The sensitivity of the 40-60-degree cracks to axial stress is greater than that of the 70-90-degree cracks. As the confining pressure decreases, the stress sensitivity of the crack to axial  
Figure 31: Contrast diagram of the seepage flow increment when the stress level changed from 30 MPa to 5 MPa. (**a**) 10 MPa and (**b**) 20 MPa. stress increases gradually. As the axial pressure decreases, the stress sensitivity of the crack to the confining pressure increases continuously. (4) The results of the typical crack models indicated that under the same stress conditions, the order of seepage flow rate, from large to small, is type III, type II, type Y, and then the 70-degree and type I models. As the confining pressure decreases, the seepage flow rate and the increment of seepage flow rate increase. As the axial pressure decreases, the seepage flow rate increases, but the increment of seepage flow rate is almost stable at a given value. The increment of the seepage flow rate (\(10^{-5}\)) when the confining pressure reduced from 30 MPa to 5 MPa was an order of magnitude greater than the increment of seepage flow rate (\(10^{-6}\)) when the axial pressure reduced from 30 MPa to 5 MPa, indicating that the permeability of cracks is more sensitive to the confining pressure than to the axial pressure.