Abstract: Using the newly developed cement mortar materials, horizontal natural fissures and inclined precast flaws were arranged in the testing specimens, and different tests were carried out under uniaxial and biaxial compression conditions. Crack propagation and penetration process under different loading conditions were analyzed in detail. The test results show that: the propagation path and direction of pre-cracks change significantly after the pre-cracks meet the natural fissures during the coalescence process, and the phenomenon of ‘displacement jump’ appears. The increase of lateral confining stress inhibits the initiation of wing cracks and secondary cracks on the inclined crack tips. Under high lateral confining stress, these cracks do not penetrate through natural fissures, and the failure mode changes from splitting to shear failure. Under the action of hydraulic coupling, the maximum principal stress distribution of the wing crack tip in uniaxial compression gradually decreases with increase of internal water pressure, and the initiation stress, initiation angle and peak strength are also gradually reduced. The crack propagation and penetration law obtained by numerical simulation is in good agreement with test results. The numerical analysis of inclined flaws with different internal water pressures extending through the waterless pressure horizontal fissures is carried out. With the increase of the water pressure, the inclined flaws firstly initiate the coplanar cracks and then generates the wing crack. When the wing crack propagates through the horizontal fissures, the expansion path also changes. Under the action of hydraulic coupling, the lateral pressure also suppresses the initiation of the wing crack. The increase of water pressure weakens the inhibition of lateral pressure on wing cracks.

Key words: inclined flaws and horizontal fissures, fissure propagation test, internal hydraulic pressure, numerical simulation