Abstract: The failure process of plane strain two bodies model composed of rock specimen that is always elastic and coal specimen that is elastic prior to the peak stress and strain-softening beyond the peak and the effect of height of rock specimen on the complete stress-strain curves of model and coal specimen, the deformation rate and failure mode of coal specimen as well as the shear strain increment within coal specimen were numerically modeled by FLAC under the condition of smooth ends (no end-restraint effect). Numerical results show that when the peak stress of complete stress-strain curve of model is reached, the pattern of shear bands within coal specimen is very apparent. In strain-hardening stage of model, strain localization of coal specimen can be seen as a precursor to the unstable failure of model. Longer rock specimen leads to (1) steeper strain-softening branch of stress-strain curve of model, as is in qualitative agreement with the previous analytical solution that longer specimen results in steeper post-peak stress-strain in uniaxial compression; (2) more ductile strain-softening branch of stress-strain curves of coal specimen and higher plastic dissipated energy consumed by coal specimen; (3) lower deformation rate of coal specimen in stage elastic; and (4) higher shear strain increment within coal specimen. The slope of complete stress-strain curve beyond the peak stress of coal specimen, the deformation rate of coal specimen in stage elastic, the shear strain increment within coal specimen and the plastic dissipated energy consumed by coal specimen are influenced by the height of rock specimen, which reflects that the effect of geometrical size of rock specimen on the deformation and failure of coal specimen and the interaction between coal and rock specimens cannot be neglected.

Key words: two bodies model, elastic rock, elastic and strain-softening coal, interaction, shear band, complete stress-strain curve