Abstract: A team of specimens containing two parallel three-dimensional(3D) cracks are made of a newly developed resin，which is completely transparent and has more brittle fracture properties of rock-like material(tension-compression ratio is 1/6.6) than before at room temperature. The propagation and coalescence process of the cracks under uniaxial loading is described and analyzed in detail; and then its produce condition and mechanism are studied. The testing results show that the failure process of specimens can be divided into four stages. The fracture of 3D cracks, which produces many different forms of cracks, is much more complex than that of 2D cracks. Subsequently, the specimen is chosen to carry out the numerical simulation. By employing FLAC3D, the propagation process of the 3D cracks are simulated and studied by establishing a new elasto-brittle constitutive relation and using superfine and reasonable form of unit division. The numerical simulation results match well with the testing results in this paper and that obtained by former scholars, so as to show the effectiveness of the new numerical simulation method. Moreover, the simulation results also have a good consistency with the testing results obtained by former scholars under biaxial loading.

Key words: two three-dimensional flaws, extending test, secondary crack and failure mode, numerical simulation, elasto-brittle constitutive relation