Experimental Study On Self-healing And Strain Hardening Of Salt Rock Damag

With the advantage of ultra-low pore permeability,good creep properties,water-soluble mining ability and damage self-healing,salt rock bodies are ideal for building underground energy storage reservoirs,but some accidents still occur during the construction and operation of salt caverns.During the mining of salt cavity,the top of cavern may collapse and the technical pipe may produce distortion and deformation;the salt rock has strong rheological properties,and the volume of the reservoir will continuously decrease under the joint action of the overlying rock pressure and ground stress;during the operation of the salt cavern reservoir,accidents such as oil and gas leakage and explosion may occur from time to time.Therefore,the stability of the reservoir during construction and operation becomes the primary consideration in the construction of salt cavern reservoirs.The study of the stability of salt cavern reservoirs during construction and operation requires a comprehensive understanding of the basic physical and mechanical properties,damage properties and the changes of properties after damage of salt rock under the action of complex environmental factors.Therefore,in this paper,based on the occurrence characteristics of salt rock itself and the actual working conditions during the construction and operation of salt cavern storage,we conducted mechanical and acoustic emission tests,pore permeation tests and nuclear magnetic tests to address the damage characteristics of salt rock and the unique damage self-healing and strain hardening phenomena of damaged salt rock,and the main research contents and conclusions are as follows:(1)Uniaxial compression + AE tests were conducted on salt rocks,and it was found that the strength,deformation and damage characteristics of salt rocks have a certain loading rate effect,and the faster the loading rate,the higher the modulus of elasticity and peak strength of the specimen,the lower the peak strain,dilation stress and volume strain,and the damage form develops from tensile splitting damage to shear damage.(2)Triaxial compression tests were carried out on salt rock to analyze the mechanical property changes,damage characteristics and damage evolution law of salt rock under different confining pressures and different displacement loading rates,and to analyze the influence and mechanism of confining pressures on the loading rate effect of salt rock by comparing with the uniaxial condition.After the triaxial test,uniaxial compression test was carried out again to analyze the change of mechanical properties after strain hardening and the influence of confining pressure and displacement loading rate on strain hardening of salt rock.It was found that the increase of confining pressure and loading rate is conducive to strain hardening of salt rock.(3)Mechanical,acoustic emission,pore-permeability and nuclear magnetic tests were carried out on salt rock to study the mechanical properties,pore-permeability characteristics and damage evolution law of different self-healing modes and self-healing time of damaged salt rock under the combined action of strain hardening and damage self-healing mechanism.The correlation factors of damage self-healing were established based on acoustic emission parameters.The damage self-healing properties and strain hardening self-weakening phenomena of salt rock are analyzed from various angles.It was found that both damage self-healing and strain hardening self-weakening of salt rocks have a fast and then slow phase change,and the confining pressure can substantially increase the rate of damage self-healing of salt rocks.