Simulation Study Of The Propagations Of Interface Crack And Sub-interfacial Crack In Layered Rock Salt

Due to its great physical and mechanical features such as densification, self-healing performance and sound plastic deformation capacity, salt rock is internationally regarded as the ideal medium for storing oil and natural gas, handling the radioactive nuclear waste and storing compressed air energy. But different from the massive salt domes in North America, salt rock deposits in China always contain interlayers. The presence of interlayers can cause deformation inconsistent near interface and lead to cracks. On the one hand crack initiation and propagation will lead to leakage, on the other hand crack initiation and propagation will change the stress field around the crack and affect the stability of salt caverns. Research on crack propagation in bedded salt rock, especially near the interface is of great significance.The propagation processes of interface crack and sub-interfacial crack in compression-shear fields in layered salt rock are simulated using Abaqus. Traction-separation cohesive behavior is introduced within the framework of extended finite element method(XFEM) to realize the simulations in which the effects of interlayer strength, interface strength, interface dip angle and crack friction are taken into consideration.Before the simulations of crack propagations of interface crack and sub-interfacial crack, simulations of crack propagations in salt rock are conducted. By comparing the simulation results with the experimental results of other researchers, the simulation method above is verified to be reasonable in terms of simulating crack propagations in salt rock. In order to verify the correctness of the method applying to interlayers, both experiments and simulations are carried out on gypsum specimens. The results shows that the simulation method is also useful to simulate crack propagations in interlayers.Simulation results of the propagations of interface crack and sub-interfacial crack in layered rock salt are as follow:(1) The new crack initiated on the basis of pre-crack is caused by local tension. The new crack dose not propagate in the direction of the pre-crack, and tends to the compressive stress direction with its forward propagation. During the entire crack propagation process, there is a stress concentration area at the pre-crack tip, and low stress zone near the area of interface edge due to crack initiation and growth.(2) The impacts of interlayer strength are small on both interface crack and sub-interfacial crack located in salt rock. But the influence of interlayer strength on sub-interfacial crack located in interlayer are of the most significance. Crack length and crack initiation angles of interface cracks and sub-interfacial cracks located in salt rock under different interlayer strengths are of rare differences. Crack paths of sub-interfacial cracks located in interlayer are also of no significant differences. Under different interlayer strengths, after the crack growth across the interface circumstances of crack paths of sub-interfacial cracks located in interlayer located are as follow: under weak interlayer circumstance, crack propagates continuously through the interface; and under hard interlayer circumstance, when the crack reaches the interface, it moves down a certain distance along the interface and then continue to extend forward, the propagation direction also changes slightly.(3) The impacts of interfacial strength on the initiation angles and crack length of two kinds of sub-interface cracks are small. And the impacts on the interface crack growth are mainly in terms of the length of the crack. Interface crack length increases with increasing strength of the interface, the interface crack initiation angles under different interface strength are basically the same.(4) Interface dip angle significantly effects crack propagation of all kinds of cracks. When the interface tilts upward, the new crack extend upward, and the new crack extend downward when the interface tilts downward. The larger the interface inclination angle, the smaller the crack initiation angle. Overall, the crack length increases with the increase of the interface inclination angle.(5) Crack surface friction significantly affects the propagation of interface crack and sub-interfacial crack, mainly in terms of crack propagation path. Under different coefficients of surface crack friction, crack initiation angles are the same or substantially the same. The crack length in interface crack model decreases with the increase of the friction coefficient of the crack surface, while the crack length in sub-interfacial crack models increases.