Experimental Study on the Dissolution Characteristics and Microstructure of Carbonate Rocks under the Action of Thermal–Hydraulic–Chemical Coupling

Microdamage in a rock induces a change in the rock’s internal structure, affecting the stability and strength of the rock mass. To determine the influence of dissolution on the pore structure of rocks, the latest continuous flow microreaction technology was used, and a rock hydrodynamic pressure dissolution test device simulating multifactor coupling conditions was independently developed. The micromorphology characteristics of carbonate rock samples before and after dissolution were explored using computed tomography (CT) scanning. To conduct the dissolution test on 64 rock samples under 16 groups of working conditions, 4 rock samples under 4 groups were scanned by CT under working conditions, twice before and after corrosion. Subsequently, the changes in the dissolution effect and pore structure before and after dissolution were quantitatively compared and analyzed. The results show that the dissolution results were directly proportional to the flow rate, temperature, dissolution time, and hydrodynamic pressure. However, the dissolution results were inversely proportional to the pH value. The characterization of the pore structure changes before and after sample erosion is challenging. After erosion, the porosity, pore volume, and aperture of rock samples increased; however, the number of pores decreased. Under acidic conditions near the surface, carbonate rock microstructure changes can directly reflect structural failure characteristics. Consequently, heterogeneity, the presence of unstable minerals, and a large initial pore size result in the formation of large pores and a new pore system. This research provides the foundation and assistance for predicting the dissolution effect and evolution law of dissolved pores in carbonate rocks under multifactor coupling, offering a crucial guide for engineering design and construction in karst areas.