## 1 Introduction  
In many slope engineering situations, the rock is in a state of continuous load, which adversely affects the slope stability, resulting in slope failure accidents and disasters such as landslides [1; 2; 3; 4]. Therefore, investigating the geomechanical properties of rocks that are under cyclic loading is important to ensure the rock structure reliability.  
To date, many studies have tried to determine the fatigue behavior of soft rock on a laboratory scale. In mining and geotechnical engineering, the surrounding rock is affected by cyclic blasting vibration, rock drilling disturbance, etc., and the stability of the surrounding rock is related to the safety of the underground structure. Therefore, the mechanical characteristics of the rock under a non-static load should be considered completely. The rocks affected by the mechanics in different environments exhibit varied properties. The main research directions of cyclic loading involve the stress and strain, and a large number of laws have been summarized in uniaxial and triaxial cyclic loading [5; 6; 7]. The main conclusions are as follows. The strength of rock is usually enhanced under the fatigue load without a confining pressure, but the opposite occurs under the condition of a confining pressure. Several mechanical tests [8; 9; 10] showed that the deformation characteristics of rock, concrete, soil, and other materials were mainly reflected in the relationship between the stress and strain, and extended toward the direction of thermodynamics, such as the input and the consumption of energy, regardless of the stress mode of the creep or cyclic load. However, changing the stress mode directly leads to changes in the strain rate. For example, different loading frequencies, stress waveforms, and loading sequences significantly impact the deformation and mechanical behavior of the test material. Cyclic load tests on sandstone, marble, coal rock, rock salt, and other rocks [11; 12; 13] have shown that the loading frequency and stress amplitude significantly affect the mechanical stress of the rock. The strain accumulation of the first and last cycles in the static loading exceeds the cumulative deformation at the intermediate stages. In the uniaxial test, the energy dissipation increases with the increase in the loading frequency. [PERSON] and [PERSON] [14] tested the properties of coal mine samples of intact sandstone under a fatigue load and demonstrated that the frequency and stress amplitude significantly affect the behavior of the rocks. [PERSON] et al. [15] conducted fatigue tests on argillaceous quartz siltstone to study the laws describing the deformation and strength changes, the mechanical parameter evolutions, and the microstructure characteristics, revealing the response characteristics of argillaceous quartz siltstone under a cyclic load. [PERSON] et al. [16] studied the influence of the maximum stress level, frequency, and amplitude of the constant amplitude cyclic loading and focused on the fatigue damage response of typical crystal and granular rock.  
The abovementioned studies focused on the static loading conditions. However, in actual engineering situations, rocks are usually disturbed by variable stress amplitudes and frequencies, and there is minimal research on the fatigue damage characteristics of soft rocks subjected to increasing-amplitude loading [17; 18; 19; 20; 21]. Therefore, the evolution of the failure mechanism of argillaceous shale samples was determined based on the stress-strain curves in this study. Additionally, the evolution of the failure process was studied via real-time acoustic emission (AE) monitoring, which allowed for examinations of the structural deterioration and fracture evolution that occurred under multi-stage cyclic loading and unloading. This loading mode is closer to the actual loading mode of the slope, which can provide basic data support for slope stability engineering.