Experimental and damage theory study on the macro and micro mechanical behaviours of rock at acidic environment

Analysing the macroscopic and microscopic mechanical properties and damage mechanism of acid-eroded rocks encountered in rock engineering construction in acidic areas is of great significance for the smooth progress of construction. Firstly, this article selects sandstone as the sample and analyses the quality change rate, density change rate, longitudinal wave velocity change rate, microstructure change, and mechanical properties through indoor acid corrosion test, scanning electron microscope observation, and triaxial compression test. Secondly, the changes in porosity of rock before and after acid corrosion are obtained using nuclear magnetic resonance technology to define the microscopic chemical damage variable, and the total damage variable of rocks under the coupling effect of chemical corrosion and confining pressure is derived. Then, based on Lemaitre strain equivalent hypothesis, the microscopic damage evolution equation and constitutive model of rock under the coupling action of chemical corrosion and confining pressure are established by using the theory of continuous damage mechanics and assuming that the rock element strength failure complies with SMP criterion. Finally, the rationality and accuracy of the model are verified by triaxial compression test data of acid-etched rock. The results show that both macro- and micro-mechanical properties of sandstone are degraded by acid etching, resulting in significant damage. The established microscopic damage constitutive model (DCM) can well reflect the stress–strain characteristics of the whole process of acid-eroded rock triaxial compression, and the test curve is in good agreement with the theoretical curve, which verifies the rationality and reliability of the model and the method for determining the model parameters. This model expands the damage model of rock under the coupling effect of chemical corrosion and confining pressure, further revealing the damage mechanism and failure law of rock under the coupling effect of chemical corrosion and confining pressure.