## 1 Introduction  
There are a large number of natural joints, cracks, structural planes, and other weak surfaces in natural rock mass [1]. These weak surfaces play a significant role in the stability of rock masses during the construction of tunnels, mining roadways, dams, slopes, and underground civil air defense projects. The stability of the rock mass directly affects the construction progress, as well as the safety during and after its use. Due to the continuous progression of surface construction, underground excavation, and mining, the load on the rock mass is subjected to varying loads instead of a constant value. Studies have shown that many rocks demonstrate an obvious loading rate effect [2]. Changes in loading rate applied to the rock mass have significant influence on the weak surface materials, creating primary or secondary cracks within the rock mass, which may continuously accelerate or slow down to close, crack initiation, propagation, coalescence, and even lead to instability and failure of rock materials [3]. In severe cases, the change of load may lead to the instability and failure of rock mass, which not only brings huge economic losses to the project, but also poses a threat to the life safety of relevant staff. Therefore, it is of great engineering significance to study the mechanical properties, crack propagation, and failure modes of fractured rock materials under sudden change in loading rate uniaxial compression, which helps to assess the damage to the rock. In recent years, both domestic and foreign scholars have conducted a lot of research on the loading rate effect of rocks by conducting laboratory tests. [PERSON] et al. [4] found that mudstone had obvious loading rate change effect and showed isotach viscosity behavior. [PERSON] et al. [2] studied that the loading rate had an effect on the crack propagation and failure mode of the rock specimen. With the increase of the loading rate, the crack generation types changed from wing crack to tensile crack, and no longer transformed to other crack types. [PERSON] et al. [5] discovered that there was obvious loading rate effect on crack propagation and acoustic emission response behavior of fractured sandstone. [PERSON] et al. [6] took clay rocks as test objects to study the loading rate effect of rocks. The results revealed that clay rocks presented a tendency to approximate linear change with the increase of uniaxial compression loading rate. [PERSON] et al. [7] researched that the peak strength of some rocks did not increase with the increase of loading rate. In the process of rock loading, the acoustic emission (AE) would have occurred in the form of stress waves when the internal crystals were dislocated or fractured. Therefore, acoustic emission technology is an effective way to monitor the failure of rock mass [8]. [PERSON] et al. [9] studied the failure process of granite using AE technology and proposed that the occurrence of significant AE events or the surge of AE characteristic parameters often corresponded to the initiation of microcracks. [PERSON] et al. [10] compared acoustic emission signals with stress-strain curves of rocks, founding that acoustic emission ringing and its energy characteristics could better reflect the activity of fracture events inside rocks and the elastic strain energy released. [PERSON] et al. [11] analyzed the mechanical properties and mesoscopic acoustic emission characteristics of prefabricated fracture cemented paste backfill under different loading rates, and concluded that the temporal and spatial distribution characteristics of AE corresponded to the crack evolution trend. [PERSON] et al. [12] further elaborated the crack coalescence and the specimen failure process under uniaxial compression using the method of combining acoustic emission technology and photographic monitoring. Most of the existing results have studied the strength failure and crack propagation of rock materials under constant loading conditions.