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Abstract By analyzing the tip stress field of compressive-shear microcrack，the initiation strength of rock mass containing crack is estimated. The results show that the initiation strength of rock mass has a relationship to the angle between microcrack and the orientation of the maximum principal stress and confining pressure. When the confining pressure increases，the initiation strength increases，but the initial angle will decreases. Only when the angle between the microcrack and the orientation of the maximum principal stress is in a certain range，the microcrack has an effect on the initiation strength of rock mass，and this range will reduce with the increasing confining pressure. Furthermore，the microcrack needs high applied force to keep propagating. Therefore，the failure of shallow engineering rock mass is mainly controlled by the penetrated cracks. The influence of microcracks on the mechanical behaviour of rock mass can be neglected when using the numerical methods.
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Received: 24 May 2010
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2011, Vol. 30 
