EFFECT OF LAYER THICKNESS OF FLAGGY ROCK ON CRACK PROPAGATION PATH SUBJECTED TO THREE-POINT BENDING

In order to reveal the influence of single layer thickness on crack propagation path of flaggy rock, we used ABAQUS for numerical simulation. We carried out three-point bending tests of layered rock with specimens' length and width constant(512 mm×128 mm). There were 5 layer thicknesses. They were respectively 64 mm, 32 mm, 16 mm, 8 mm, and 4 mm. Information of acoustic emission and main crack path were extracted. We summarized the regulation of peak load and acoustic emission data. The results of the study show that:(1)The strength of flaggy rock is relevant to single layer's thickness. The larger the monolayer thickness is, the smaller the bending strength of rock mass is, meanwhile this change is nonlinear. (2)Although with different thickness, the bedding surface consistently shows the effect of preventing crack propagating upward. (3)With monolayer's thickness decreasing, the total crack length of rock mass first increases and then decreases. (4)When the cracks expand along the weak surface, the fracture type is a combination of slip and tensile fracture. In contrast, when they expand inside the rock mass, tensile fractures dominate. (5)Acoustic emission event will not occur instantly. In the contrary, they increase sharply just when the peak intensity approaching. Accompanied by the stress plunging, the number of acoustic emission events reaches the maximum. The research results will provide a basis for predicting the fracture process of layered rocks.