To investigate the influence of carbon fiber reinforced polymer (CFRP) strip with different number on the creep mechanical properties of coal samples under axial compression, a coupled numerical simulation using PFC^3D and FLAC^3D software was conducted, and a hybrid contact model combining the Burger’s model and the Linearpbond model was established. The reliability of the numerical model was validated based on laboratory uniaxial compressive creep tests of unconstrained coal and coal samples constrained with 6 strips of CFRP sheet. The mechanical properties and energy evolution of coal samples constrained with 2 to 7 strips of CFRP sheet under uniaxial compression were studied by numerical simulations. The results show that as the number of strips increases, the initial axial strain of the coal sample tends to increase overall, with a significant increase in axial strain during the accelerated creep stage, and the maximum internal contact force in the hybrid contact model tends to increase overall. The ratio of the contact quantity of Burger’s model to that of Linearpbond model is about 1∶9, and this ratio in the numerical simulation model could reflect the creep mechanical properties of coal samples. Increasing the number of CFRP strips restricts radial deformation, increases the number of shear micro-cracks, causes more severe shear damage within the coal sample, and the failure mode of the coal sample changes from tensile failure to shear failure. As the number of strips increases, the total energy, elastic energy, and dissipated energy all increase, and the change in elastic energy is similar to the change in total energy before the coal sample experiencing creep instability.

To investigate the effects of different layers of carbon fiber reinforced plastic (CFRP) on the mechanical properties and energy evolution of axially compressed cylindrical coal samples, the finite difference method-discrete element method (FDM-DEM) coupled numerical simulation and laboratory uniaxial compression tests are combined in this paper. The test results show that both unconfined cylindrical coal samples and CFRP-confined samples undergo four stages in the stress-strain curve, namely, compression-tightness, elasticity, yielding, and post-peak. The CFRP-confined samples show obvious ductile damage in the yielding and post-peak stages, and their average peak stresses, peak strains, and elasticity modulus are about 2, 2.5 and 1 times higher than those of the unconfined samples, respectively. Numerical simulations show that the peak strain and peak stress increased to 733% and 548%, respectively, with the increase in the number of CFRP layers. The elastic modulus does not increase monotonically, indicating that a balance between strength and stiffness is required when designing the CFRP layers. In addition, the increase of CFRP layers leads to the change of the damage mechanism from tensile damage to shear damage, indicating that it has a significant effect on the stress distribution and damage process of the cylindrical coal samples. The total and dissipated energy of the cylindrical coal samples significantly increased with the increase of CFRP layers, and the energy absorption efficiency reaches up to 10.51 times, showing a significant enhancement of their destabilization resistance. To quantify the confinement effect of CFRP sheets, the concept of “equivalent thickness” is introduced. It is found that the equivalent thickness increases nonlinearly with the number of CFRP layers, and at 6.78 layers, the equivalent thickness approaches infinity, which emphasizes the importance of CFRP sheet in improving the stability of cylindrical coal sample structure, and provides an important reference for future research.

Carbon fiber-reinforced plastic (CFRP) wrapping is a promising technique for enhancing the structural integrity of coal columns. When applied to coal columns in roadway environments, CFRP reinforcement offers significant advantages over unreinforced columns. Specifically, the compressive strength of coal columns subjected to triaxial compression is markedly higher than that of columns subjected to uniaxial compression, primarily due to the restricted lateral expansion in the former case. This study investigates coal column specimens with varying CFRP layer configurations and net spacing ratios, evaluating mechanical properties such as stress-strain behavior, peak strength, and ultimate strain through uniaxial compression testing. The research explores the impact of CFRP confinement on the mechanical performance and damage modes of coal columns under different conditions. The results indicate that coal columns confined by CFRP strips or fully wrapped with CFRP exhibit similar mechanical behaviors. CFRP strip confinement provides a notable strengthening effect under uniaxial compression, with peak strength and deformation resistant capacity significantly improved as the net spacing ratio decreases and the number of CFRP layers increases. Additionally, the CFRP reinforcement effectively mitigates lateral expansion, alters the failure mode, and delays the onset of damage. Furthermore, using the Richart and Hoek-Brown models, the study incorporates the test data for model refinement and comparative analysis, leading to the development of a modified Richart strength model for CFRP-constrained coal columns.