## 1 Introduction  
During the process of mining and tunnel excavation in coal mines, structures and fractured zones are often encountered in front of the working face. If no protective measures are taken, there are safety risks. Advance pressure grouting fills cracks in coal and rock masses, generates a bonding force, and enhances the strength of the coal and rock. Moreover, advanced pressure grouting has the advantages of flexible construction and a greater distance. It is widely used in coal mines for advanced reinforcement to enhance the stability of the working face in fractured coal and rock areas, ensuring mining safety. Owing to the relatively long solidification time of grout and its effect on production efficacy and construction progress, the adjacent working face or the working face is often advanced without waiting for the grout to fully solidify during actual production processes. Thus, the advanced grouting area is subject to varying degrees of early disturbance, leading to initial damage to the coal-cement grout that affects the mechanical properties of the final-set coal-cement grout. Therefore, to better determine the timing for the recovery of near-working surfaces after pre-grouting, it is necessary to study the effects of different early damages on the physiomechanical properties of coal-cement grout. To explore the effects of early damage on the original coal and concrete mechanical properties, [PERSON] et al. [1] performed a cyclic loading and unloading test on a coal-rock mass to produce varying degrees of early damage and analyzed both the dynamic mechanical characteristics and the damage and fracture mechanism of the coal in the early stages of interference. The results showed that early interference in the coal sample produced more new cracks, which expanded as the degree of damage increased, leading to a gradual weakening of the mechanical properties of the coal. [PERSON] et al. [2; 3] applied varying degrees of early stress to coal samples and analyzed the effects of early interference on the strength characteristics and creep failure regularity. The results suggest that the steady creep rate increases gradually with an increase in the degree of early damage, establishing a relationship between early damage and rupture damage based on creep rules and improving the creep model at the acceleration stage. When the static load at different early damages affects concrete, concrete exhibits stronger damage and strain-rate effects, and the extent of damage after exceeding a certain limit value has a significant impact on the dynamic compressive strength of concrete [4]. [PERSON] et al. [5] prepared experimental cube concrete with various initial defects and performed uniaxial compression tests using the acoustic emission (AE) technique. The results indicated that the test block strength significantly decreased and early damage increased, indicating that the AE counts can reflect the failure law during each stage. [PERSON] et al. [6] studied the law of strength in different-sized concrete samples in various early damage situations. Their results showed that with an increase in the degree of early damage, both the static and dynamic compressive strengths decreased, and early damage had a more significant effect on dynamic compressive strength than on the static compressive strength. In terms of the mechanical properties and failure mechanism of grout-reinforced bodies, [PERSON] et al. [7] performed orthogonal tests on fractured coal with variable sizes and cement paste with different water-cement ratios. The mechanical properties of the injections and crack destruction characteristics were analyzed using an effect-evaluation test machine for grouting reinforcement. By varying the rubber particle content and admixture in an orthogonal design experiment, [PERSON] et al. [8] studied the influence of grouting materials on the mechanical properties, permeability, and microstructure of grout-reinforced bodies. [PERSON] et al.