STUDY ON TENSILE FAILURE CHARACTERISITCS OF NATURAL FRACTURED ROCK BASED ON CT-CA

The natural damage such as cracks and holes in rock can have important impact on the mechanical properties and failure process of rock. Using the cellular automata theory and CT nondestructive identification technology,we study the whole process of crack propagation and coalescence and the change law of mechanical properties of rock containing natural cracks under splitting conditions. Based on the real micro-structure of fractured sandstone,we construct the numerical calculation model of natural fractured rock,complete the numerical test of sandstone splitting failure with different fracture dip angles,and analyze the influence of fracture dip angle on the mechanical properties,crack propagation process and energy evolution of sandstone. The results show that:(1)The tensile strength of fractured sandstone is closely related to the fracture dip angle. With the increase of fracture dip angle,the tensile strength decreases first and then increases. (2)The fracture starts at the tip of the initial fracture. When the dip angle is greater than 0° and less than 48°,the staggered crack causes the failure of the rock sample,and the main crack propagates along the vertical direction near the initial fracture; When the dip angle is greater than 48° and less than 94°,open crack causes the failure of rock sample,and the main crack propagates along the parallel direction with the initial crack. (3)There are tensile stress zone and compressive stress zone at the crack tip during the splitting process. The tensile stress causes the wing crack to initiate and propagate along the natural crack tip,while the compressive stress causes the secondary crack to propagate along the original crack direction. (4)We divide the energy evolution of the splitting failure process of sandstone with natural fractures into four stages. With the increase of fracture dip angle,the total energy density and elastic energy density at the peak point decrease slowly and then increase rapidly,but have little effect on the dissipation energy of rock samples.