Experimental analysis on dissolution characteristics of carbonate rocks in Liaoshan tunnel of Emei−Hanyuan expressway in Sichuan Province

The Liaoshan tunnel is one of the controlling projects of the E-han expressway, the karst geological conditions in the tunnel site area are complex. In order to deeply study the characteristics of carbonate dissolution in the field, this paper takes the typical dolomitic limestone, limestone and calcareous mudstone samples of the Mesozoic Triassic Middle Leikoupo Formation in the tunnel site area as the research object to carry out the static corrosion simulation experiment. The characteristics of dissolution rate of carbonate rock and related factors are analyzed quantitatively, and the changes of microstructure in the process of sample dissolution under SEM are discussed qualitatively. The results show that: (1) Under the experimental conditions (20 ℃, 1 atm, acetic acid solution, pH≈5.30, static dissolution), the dissolution rate of limestone in Leikoupo Formation is about 3.48 mm/a, that of dolomitic limestone is about 1.57 mm/a, and that of calcareous mudstone is about 0.90 mm/a. (2) The dissolution of carbonate rocks is controlled by the mineral composition and dissolution environment. Under the same dissolution environment, the dissolution rate of carbonate rocks is positively correlated with the content of calcite, and negatively correlated with the content of dolomite and the pH value of the dissolution medium, and generally characterized by limestone>dolomitic limestone>calcareous mudstone. (3) Under the environment of organic acid and inorganic acid, the dissolution rate of limestone has little difference and the general trend is the same, while the neutral salt solution and alkaline environment have different degrees of inhibition on the dissolution of limestone. (4) Carbonate rock has the characteristic of preferential selective dissolution along mineral composition and rock microstructure. The difference of the main mineral content also makes the micro dissolution process of the carbonate rock different.