Abstract: Grouting is a widely used and effective method to enhance the strength of soft, fractured surrounding rock and maintain engineering stability. In order to evaluate the impacts of grouting on mechanical properties and fracture damage of coal and rock, uniaxial compression tests were conducted on samples before and after ultrafine cement grouting. Digital image correlation and acoustic emission technologies were employed to monitor damage evolution and crack growth in coal and rock. The process of crack tip grouting expansion was discussed using fracture mechanics theory. The results show that: 1) Compared to intact coal samples, the strength increase post-grouting. Coal samples with more cracks exhibit lower strength, potentially due to stress concentration at crack tips. 2) Post-grouting, internal pores in the coal sample are filled, reducing brittleness and enhancing plasticity and deformation resistance. However, grouting minimally affects post-peak deformation, and the cementation between grout and coal is suboptimal. 3) The failure of intact coal samples primarily exhibits a single high-strain concentrated zone. In grouted coal samples, grouting enhances the isotropic of the mechanical properties failure lacks a in distinct strain concentrated zone, and strain evolution is relatively disordered. 4) The horizontal displacement damage factor Dw is proposed to characterize the damage evolution degree of coal under uniaxial load, the horizontal displacement damage variable is defined, and the damage piecewise constitutive model for uniaxial compression coal sample is established.

Key words: grouting reinforcement, crack propagation, damage factor, constitutive model