It is important theoretical significance and application for the failure mechanism of rock and parameter selection of fracture surface that failure property of rock and roughness of fracture surface are studied. The unloading fracture property of rock

micro-mesoscpic characteristics of fracture surface

and the correlation between fractal dimension of fracture surface roughness and unloading rock mass strength are revealed under high stress

by adopting high precision of three-dimensional 3D laser scanning and scanning electron microscope (SEM)

combined with fractal theory. The macro-fracture property of marble specimen is converted from shear and tensile-shear complex to tensile fracture development. The higher the initial confining pressure and the faster the unloading rate

the main fracture surface is more fluctuant and rough. But The higher the initial confining pressure and the slower unloading rate

the main fracture surface is more flat and smooth. With the increase of unloading rate

the microscopic fracture of the marble is gradually from traverse crystal sheared

tensioned-sheared complex along crystal face and traverse crystal

to tensioned or splited along crystal. The friction angle of unloading rock is larger

but the cohesion is smaller with the fractal dimension of main fracture increases.