Abstract: To investigate the deterioration rule and failure criterion of rock in the acid-based environment, experiments were conducted on sandstone specimens after 1, 5, 10, 15, and 20 times of wetting and drying cycles in the environment of pH=7, 5 and 3, respectively. By analysing uniaxial compressive strength (UCS) and triaxial compressive strength (TCS) after different cycles, the parameters of Mohr-Coulomb failure criterion and Hoek-Brown failure criterion were calculated, and the effect of wetting and drying cycles on these parameters is also analysed. Finally, according to the relationship formula between the deviatoric stress and the strength criterion parameters in the stress space, the failure envelopes changed with cycles in the π-plane were drawn under the action of solutions with pH values of 7, 5, and 3. The results show that the parameters of strength criterion decrease with the increase of cycle time, at the early stage of cycles, the deterioration is more significant, and then the deterioration is relatively low. The lower the pH value is, the more serious the deterioration is, and the degrees of deterioration effect from large to small are as follow UCS, cohesion, material constant and internal friction angle. In the same environment of pH value, when the cycle number is low, the failure envelopes in the π-plane are relatively sparse. However, the greater the number of cycles are, the denser the failure envelope is; in the different immersion environment of pH value is, the lower the pH value is, the smaller the failure plane is. The deviatoric stress is positively correlated with UCS and cohesion, but negatively correlated with the material constant and internal friction angle.

Key words: wetting and drying, sandstone, deterioration, π-plane, failure criterion