Experimental Study on Failure Mechanics Characteristics of Salt Rock under Tensile Loading and Unloading Conditions

摘要

By use of the MTS815 Flex Test GT rock mechanics test system and the PCI-II acoustic emission (AE) test system, the failure mechanics tests of the salt rock under the condition of indirect tensile and direct tensile loading and unloading were carried out. The test results show that the tensile strength of pure salt rock under indirect tensile cyclic load is about 1.823 MPa, and the tensile strength under direct tension is about 0.585 MPa, the tensile strength of salt rock under cyclic loading is far lower than that of compressive strength; the direct tensile tensile strength of salt rock is affected by impurities. The post peak deformation of pure salt rock under indirect tension and direct tension shows a slow decline, but the deformation after direct tensile peak of impure salt rock is brittle, and the turning point of the stress-decline slope is more obvious than that of pure salt rock. The spatial distribution and evolution of AE during indirect tensile and direct tensile failure show that the damage mechanisms of the two tensile modes are different. Under the influence of the compressive stress of indirect tension, the AE event occurs earlier on the predefined failure surface; under direct tensile load, the damage occurs later, and the degree of AE accumulation on the failure surface is far less than that of indirect tension. It is further revealed that the characteristic parameters of AE under direct tension are in a quieter period before 20% F, and the AE is active in the post-peak deformation stage; under the indirect tensile load, the AE characteristic parameters are changed in the "low tide period-active period-second active period". Indirect tensile and direct tensile AE activity in the process of unloading variation characteristics are different, the former is affected by compressive load stress, AE is relatively active in the unloading process, while the latter has no significant AE activity.