Experimental study on the dynamic acid water weakening mechanism of limestone

The water weakening function is essential for long-term stability analysis and instability prediction of rock mass. Based on the mechanism analysis，a dynamic water weakening function to characterize the strength deterioration of dissolved carbonate rocks is proposed. X-Ray diffraction(XRD) of the rock mineral and scanning electron microscopy(SEM) experiments reveal that the calcite mineral content of Maokou Formation limestone is more than 99.6%. The acid etching can hardly change the proportion of material components but can aggravate the growth of dissolution pores，holes，and gaps and weaken the strength of limestone. The uniaxial compressive strength and dynamic softening coefficient were obtained from mechanical tests. The uniaxial compressive strength of the acid-etched limestone decreased between 50.8% and 57.2%，and its deterioration degree was higher than that of other stress states. The dynamic softening coefficient decreases with the increased etching time，which negatively affects the long-term stability of rock mass. The acid erosion rate，free acid absorption rate，saturated water absorption rate ， and dynamic saturation were obtained from the water physical properties experiment，which revealed the influence of acidity and acid etching time on the difference in limestone dissolution. Acidity plays a primary role，but acid etching time determines the deterioration process of limestone in a weak acid environment. The decrease gradient of the dynamic water weakening function in the strong acid environment(pH = 2) is significantly larger than that in the weak acid environment(pH = 6)，and the maximum error between the predicted data of the fitting formula and the experimental results is less than 10%. The research results can provide critical support for studying dissolution rock mass deterioration and preventing and controlling geological disasters. © 2023 Academia Sinica. All rights reserved.