# Hydraulic Fracture Propagation in Fractured Rock Mass
## 4 Conclusions  
Hydraulic pressure field and stress field interaction is an important characteristic of rock which cannot be ignored. Seepage fluid pressure changes the stress state on the crack surface, and aggravates the trend of the micro-fracture and the faulty degradation of the fractured rock mass. According to the rock fracture mechanics criterion, the initiatory cracking law and evolution law of the stress intensity factor at the tip of the wing crack concerning the compressive-shear fractured rock under high hydraulic pressure are discussed, and the critical hydraulic pressure value, initial crack intensity criterion, and the wing crack propagation mechanics model are studied when compression-shear failure occurred and four rock-bridge fracture damage criteria are established. Besides, the relationship between compression shear coefficient of the Zhou Qunli compression shear theory and hydraulic pressure, confining pressure and the crack angle is also explored. The following conclusions were obtained. (1) Theory results indicate that crack initiation strength is inversely proportional to hydraulic pressure, the existence of hydraulic pressure aggravates the wing crack's growth, and the action of the wing crack under high hydraulic pressure extends from stable expansion into unstable expansion; the rock mass strength is proportional to the confining pressure, the stress intensity factor of wing cracks decrease with the increase of remote field stress \(\sigma_{3}\), and the wing crack tends to expand stably; the cracking strength decreases initially, then increases as the crack angle increases. This theory will provide the basis for the economic and efficient investigation of the compressive-shear destruction of fractured rock under high hydraulic pressure. (2) Based on the criterion of compression-shear fracture of Zhou Qunli, the hydrodynamic coupling action of fractured rock compression shear fracture criterion is established, and the relationship between the compression shear coefficient \(\lambda_{12}\) and hydraulic pressure, confining pressure, and the crack angle is clarified, and it is found that they are correlated with the stress in density factor \(K_{I}\), while the stress intensity factor \(K_{II}\) maintains a relatively constant value. The smaller the hydraulic pressure, the larger the confining pressure, and the larger the crack angle, the higher the stress intensity factor \(K_{I}\) value, while the compression shear factor shows the opposite. In addition, the effects of hydraulic pressure and confining pressure on the stress intensity factor \(K_{I}\) show a linear law, while the crack angle shows an exponential function growth law, and all three factors show a nonlinear relationship with the compression shear factor \(\lambda_{12}\). (3) The critical crack initiation angle, critical length of wing crack, and critical stress intensity factor of rock crag penetration damage are derived for the four types of rock crag shear damage, which mainly occur in wing crack, shear crack, and wing crack-shear crack mode penetration under high hydraulic pressure. In addition, when the values of the rock crag angle and the crack angle are equal, the rock crag is prone to pure shear penetration, and the high hydraulic pressure only has a splitting effect on the wing crack, and the mode is less likely to occur as the fracture dip becomes larger. (4) This study did not adopt the damage mechanics theory to further establish the evolution equation of the permeability tensor under high hydraulic pressure, and only explored the crack initiation and wing crack expansion law of rock crack under compression-shear stress state and high hydraulic pressure, as well as the establishment of the compression-shear wing crack expansion model, but did not analyze the tensile-shear stress state. Similarly, there are many kinds of crag bridge damage fracture modes; this study gives four kinds of crag bridge damage mode criterion quasi-measurements, and further research is needed for follow-up.