Abstract: The prominent characteristic of the surrounding rock of tunnel is its capacity after it was broken. Correct evaluation of the strength characteristics and deformation behavior of the broken surrounding rock have an important significance on the surrounding rock stability control. In this paper, taking acquired cracked rock samples from the failure surrounding rock in km deep mine as the research object, according to the low even approximate to zero confining stress states of the broken surrounding rock, re-fracture tests of the cracked rock samples have been conducted by the MTS machine under uniaxial compression to study its strength characteristics and deformation behavior systematically. The results show that the fracture plane has obvious effect on the uniaxial compressive peak strength, but it has no direct and decisive influence on the residual strength; the stress-strain curves of cracked rock samples can be generally divided into two types, single peak and multi-peak; the fracture plane has no obvious effect on secant modulus，the Poisson’s ratios and peak axial strain, but it has obvious influence on peak hoop strain and volumetric strain; there is a close relation between the expansion process and failure mode of the fracture plane and angle of the main rupture surface—when the direction of loading direction is consistent with main rupture surface, failure mode is mainly vertical splitting, on the contrary, when the direction of the former is perpendicular to the latter, it is mainly vertical splitting holing through the main rupture surface, and combination of shear and splitting mainly occurs in other situations. The distribution of the fracture plane on surface of the cracked rock samples shows obvious fractal characteristics, and the uniaxial compressive peak strength is a linear monotone minus function to the Box Counting Dimension.

Key words: uniaxial compression, cracked rock samples, re-fracture, failure mode, fractal dimension