Experimental study on mechanical properties deterioration of limestone in acid environment based on nuclear magnetic resonance

In order to discuss the deterioration degree of macroscopic mechanic properties and damage rule of micro structure of limestone under the condition of acidic environment,the limestone of a mine roadway in Chongqing was se-lected for study. The limestone specimens were immersed in solutions of pH = 3,5,7 at the same time and then meas-ured by NMR system to obtain the change rule of porosity. Compared with the dried limestone,the deterioration rule of mechanical properties of pre-immersion specimens were obtained from conventional triaxial experiments. The results of NMR measurements show that the porosity of limestone have a tendency to become larger in acid environment with the high formation rate of secondary macroporosity in pH = 3. Compared with the initial state,the porosity of specimens in-creases 12. 15% ,6. 67% ,3. 43% respectively in pH = 3,5,7. The results of mechanical test shows that the ductility of limestone is more obvious under the acidic conditions and a smaller stress drop after peak is observed with the increase of pH value. Except elastic modulus exhibits a secondary decrease,mechanical parameters (uniaxial peak stress,Poisson’s ratio,internal friction angle,cohesion) exhibits a linear decrease basically with the decrease of the pH value. In addition,the effect on deformation parameters is greater than the strength parameters of limestone with the deterioration of porosity under the acidic environment. And the influence degree of cohesive is greater than internal friction angle.