## 1 Introduction
[9] used a self-designed grouting test system to carry out digital quantitative analysis of the three-dimensional crack morphology and structure of coal samples subjected to load damage before and after grouting. Using a video meter, [PERSON] et al. [10] analyzed the changes in the microstructure and mechanical properties of the rock samples before and after grouting after uniaxial compression tests. [PERSON] et al. [11] compared and analyzed the strength characteristics of samples simulated by similar materials with and without grout-filled cracks. [PERSON] et al. [12] discovered through SEM and X-ray diffraction experiments that the microstructure of the bonding reinforcement is crucial for affecting the macro-mechanical properties. [PERSON] et al. [13] found that grouting reinforcement can significantly change the normal and tangential mechanical properties of fracture surfaces in a rock mass, and the strength and stability of the rock mass are enhanced by increasing the tangential shear strength with normal stress. Currently, the internal structure and damage behavior of samples are investigated mainly by AE, digital image correlation (DIC) technology, and scanning electron microscopy (SEM) technology. Based on AE positioning technology, [PERSON] et al. [14] analyzed the influence of the position, angle, and size of coal-rock fractures and developed principles concerning the injection of grout into a bulk rock mass. [PERSON] et al. [15] used DIC technology and other methods to study the fracturing properties of cross-joint samples in the loaded destruction process. [PERSON] et al. [16] combined the macro- and fine-destruction characteristics of samples according to the cross-sectional morphologies characterized by SEM, the resultsof which suggested that the graphene oxide in the slurry can promote the hydration reaction and improve the perforation structure of the injection slurry. [PERSON] et al. (2017) carried out three-point bending tests on high-temperature treated granite; the AE location and DIC technology were used to analyze the link between the rock crevice extensional regularity and the pattern of destruction. Using AE location and DIC technology, [PERSON] et al. (2018) analyzed the effects of different factors on rock damage and rupture evolutionary laws. [PERSON] and [PERSON] (2019) conducted AE signaling and DIC surface position observations for concrete prepared from two additives and reported on the evolution of concrete fractures in three-point bending trials. In summary, domestic and foreign scholars have performed a large number of studies by applying various experimental methods to determine the mechanical properties of initial coal and concrete damage and grout-reinforced rock-body mechanical characteristics, among others. However, investigating the effect of its mechanical properties following early interference of the coal-cement grout after the reinforcement of the coal-rock mass has significant engineering value and theoretical significance. Thus, this article reports the use of grouting equipment designed and built in our laboratory to inject fractured raw coal. Uniaxial compression was applied to the injected samples to examine the early damage to the coal-grout rock body after the initial setting. After the final setting, uniaxial compression tests were conducted, combining DIC and AE technologies to analyze the location, evolution characteristics, and failure mode of cracks during the loading and failure processes of the rock body. The microstructure of the compression fracture surface of the rock body was scanned by SEM to analyze the combined characteristics of grouting materials and raw coal, ultimately obtaining changes in the mechanical properties and fracture mechanisms of coal-cement grout with variable early damage.