Experimental Study On Shear Damage And Self-healing Of Salt Rock

With the rapid development of our country’s economy, the demand for natural gasis also growing. It was predicted that the demand will reach300billion cubic meters ofnatural gas in our country in2020, the capacity of underground gas storage will be atleast45billion cubic meters. Gas storage construction is in a long way. Salt rock is theideal medium of building energy storage, but some accidents will happen in the processof salt cave building and operating. In the process of mining, such as the collapsing ofroof, distortion of technical pipelines and so on; Due to the rheological characteristics，overlying rock pressure and far field stress will lead salt cave reservoir volume decrease;During the period of gas storage operation, it is easy for leakage of oil and gas, leadingto gas storage explosion accidents. Therefore, research on the stability of salt rock gasstorage become the first question to figure out in gas storage construction.In the process of gas storage construction and operation, intact surrounding rockunder the action of complex environmental factors, will generate unexpected injury; Inaddition, salt rock has the recoverability, which is very beneficial to the service life ofgas storage and operating stability. So according to the occurrence characteristics of saltrock itself and practice of engineering construction, focusing on the regularity of injuryand self-healing for pure and impure salt rock, the shear test, three point bending test,the Brazilian splitting test and the recovery test under the condition of constanttemperature were carried out, the damage characteristics and damage evolution law oftwo kinds of salt rock were studied under different loading ways, self-healingmechanism were analyzed under the condition of constant temperature, and a new sheardamage evolution model was put forward, and the new recognition on self-healing wasproposed. These are hoped to provide help for engineering practice and scientificresearch.(1) The compression-shear test was carried out for pure and impure salt rock,damage characteristics of different loading conditions were analyzed for two kinds ofsalt rock in the shear angle, loading rate and the way of loading direction, and on thebasis of predecessors’ efforts, a damage evolution model was built on pure salt rockunder the condition of compression-shear.(2) The compressive strength of salt rock is greater than the shear strength, and theshear strength is greater than the tensile strength. The peak shear stress and shear modulus shift obviously with different loading ways for salt rocks under the conditionof compression-shear, which is different from the general characteristics of the rock; Itwas found that under the condition of compression-shear, placed angle had the greatestinfluence on the mechanical properties of salt rock, and the influence of loading rate isnot very obvious. For repeated loading of specimens, loading direction has a greatinfluence on the damage evolution process of salt rock.(3) With the aid of acoustic emission technology, the acoustic emission signal ofsalt rock material was collected in the process of loading. The acoustic emission signalof salt rock performance very obviously from the beginning of loading, but the peak AEcounts is not related obviously to the peak stress; For repeated loading specimens，it wasfound that the acoustic emission signal is obvious in the beginning of the second load.(4) The constant temperature recovery environment was used and the rule ofself-healing for damaged salt rock was studied, self-healing features was analyzed indetail, the mechanism of self-healing was studied, and a new understanding onself-healing for damaged salt rock was put forward.(5) The law of self-healing for damaged salt rock under constant temperaturerecovery environment is coincident with the new understanding on self-healing, itsmechanical characteristics appear a certain degree of recovery. Comprehensivelyconsidering, the recovery of damaged specimens is mainly reflected in the integrity ofsalt rock; the self-healing characteristic of damaged salt rock shows evident time effect.7days is the cut-off point of short-term recovery and long-term recovery.