Damage and deterioration mechanism of marl under acidic erosion and dry-wet cycles: A case of Wuxia, Three Gorges Reservoir area

In view of the geological disasters caused by the deterioration of rock mass in the fluctuation zone of the Three Gorges Reservoir area, the marl of the Wuxia section was selected as the object, and laboratory acid corrosion and wet-dry cyclic tests were conducted to reveal the damage and deterioration mechanism of marl in the fluctuation zone with acidic environment. The results show that: (1) When the pH was 3, 5 and 7, the mass loss rate was 0.019%~0.066%, 0.010%~0.029% and 0.006%~0.017% with 5 ~ 15 circles, respectively. (2) When the pH values were 3, 5 and 7, after 15-time acidic erosion and dry-wet cycles, the average porosity increment of the samples was 0.104%, 0.093% and 0.092%, respectively, and the initial porositywas found to influence the rate of porosity increase during the early stage of the experiment. (3) At the microscopic level, the pore volume and crack length were increased, and the number of pores and cracks increased under the scanning election microscope analysis, which revealed the damage and deterioration mechanism of samples. (4) The uniaxial compressive test of the sample was inversely proportional to the number of acidic erosion and dry-wet cycles. At pH values of 3, 5, and 7, the reduction rate of rock uniaxial compressive strength ranged from 5.65% to 28.25% after 5, 10, and 15 cycles of acid corrosion-drying-wetting, respectively. (5) The variation range of the mass loss rate, pore growth rate and the uniaxial compressive strength reduction rate of rock samples were all initially slow, later fast and then slow, and finally tended to be stable. (6) The error between the result of calculation with uniaxial compressive strength fitting formula and the test is less than 10%, which could prove the fit is reasonable, universally. The research could provide theoretical support for unstable rocks mass of geological disasters in the Three Gorges Reservoir area.