Abstract: Disturbance induced by the construction of dams, tunnels and other engineering activities occurs in the surrounding rock mass and causes additional water pressure in the water of rock mass fracture. Thus, the unstable rock fracture propagates along the fissured surface under the disturbance load and fissure additional water pressure. Firstly, an analytical expression of fissure additional water pressure caused by the disturbing load is derived based on the inclusion theory, which is verified by numerical analysing. Then variation regularity of fissure additional water pressure is analysed under different rock mechanical properties, fracture shapes and inclination angles. Secondly, considering the influence of fissure additional water pressure, an analytical formula of fracture strength of rock mass is deduced by using the compressive shear fracture criterion. Finally, the effect of fissure additional water pressure on fracture strength is further investigated with an example. The results show that fissure additional water pressure reduces the fracture strength and increases the inclination angle range of fracture failure, which makes the rock mass more prone to hydraulic fracturing along the fissured surface. In addition, rock elastic modulus, fracture shape coefficient and inclination angle can have a significant influence on the additional water pressure. The fracture strength of rock mass increases with the increase of rock elastic modulus and fracture shape coefficient, and its increasing trend is more significant with the increase of fracture inclination angle.

Key words: fractured rock mass, fissure additional water pressure, hydraulic fracturing, fracture strength