## 1 Introduction  
Over the past few decades, China has made great progress with regard to the construction of large-scale water conservancy projects, such as the Three Gorges Dam, the Baihetan Arch Dam, and the Gezhouba Dam. These infrastructures have greatly improved people's lives and the economy, but they have induced a few unnoticed risks to the security of reservoir bank slopes [1; 2; 3]. For instance, the water level in the Three Gorges Reservoir area repeatedly fluctuates between 145 m and 175 m throughout the year. The frequent action of drying\(-\)wetting cycles can lead to a decline in the performance of slope rocks [4]. Moreover, the water in nature is commonly acidic rather than neutral due to the atmospheric environment, industrial sewage, and acid rain [5; 6]. As a consequence, slope rocks are exposed to complex conditions with the coupling effect of drying\(-\)wetting cycles and acidic solutions, resulting in a rapid deterioration of the performance of rocks, especially the mechanical properties. This weathering process has a complicated deterioration mechanism and a large degree of deterioration, and it may cause the occurrence of geological disasters. Therefore, studying the deterioration laws and deterioration mechanism of the mechanical properties of rocks under the coupling effect of drying\(-\)wetting cycles and acidic solutions is crucial for the prevention of geological disasters and the stability of reservoir bank slopes. It has long been recognized that the mechanical behavior of rocks changes gradually under the effect of environmental factors, such as water and temperature [7; 8; 9]. The action of drying\(-\)wetting cycles is actually associated with the two factors [10]. Increasing drying\(-\)wetting cycles deteriorates the mechanical parameters of rocks, such as the peak stress, elastic modulus, cohesion, and internal friction angle [11; 12; 13]. [PERSON] et al. [14] found that the cyclic drying\(-\)wetting could result in the dissolution loss of various minerals, an increase in porosity, and the formation of voids and fractures in the sandstone. These changes ultimately contributed to a reduction in rock strength. [PERSON] et al. [15] also observed a decreasing trend in the strength of hard rocks subjected to drying\(-\)wetting cycles. [PERSON] et al. [16] indicated that more micro-cracks were generated inside the rock with the increase in drying\(-\)wetting cycles, and this was the reason for the deterioration in the strength and deformation characteristics. According to the test results of ignimbrites after different drying\(-\)wetting cycles, [PERSON] [17] proposed linear regression models to evaluate the long-term physical and mechanical properties of building stones under atmospheric conditions. Most of the investigations have focused on the weakening effect of drying\(-\)wetting cycles on rocks in a neutral environment, while rocks are more likely to be in an acidic or alkaline condition. A few studies found that the mechanical parameters of rocks also decreased with the increase in the number of drying\(-\)wetting cycles in acidic solutions, and the solution with a lower pH value could lead to a more severe deterioration of mechanical properties [18]. For instance, [PERSON] et al. [19] and [PERSON] and [PERSON] [20] investigated the fracture characteristics of the sandstone subjected to drying\(-\)wetting cycles in solutions with different pH values. They indicated that the acidic solution had the greatest performance degradation, followed by the alkaline and neutral solutions. [PERSON] et al. [21] investigated the uniaxial compressive strength degradation of the basalt under the coupling effect of chemical solutions and drying\(-\)wetting cycles. They also pointed out that the degradation effect of drying\(-\)wetting cycles on the strength was distinctly different, and the degradation in the acidic solution was more severe than that in the other solutions. [PERSON] et al.