Rock consists of mineral grains at the mesoscale. The grain boundaries form an interface network and grain sizes are also uniformly distributed. Besides mechanical properties of mesostructure

the geometrical characters (i.e.

topology of grain interface network and grain size distribution) also contribute to fracture energy. The aim of this paper is to explore the effects of geometrical characters on the fracture energy and get insight into the mesomechanism of macro fracture energy of rock. Three-point-bending tests are carried out on marble specimens to obtain the fracture energy of marble. Then a rock slice is taken from fracture surface to obtain the image of mesostructure of rock using the scanning electron microscopy (SEM). The technique of digital image processing is used to obtain the grain interface network. Through analyzing of the interface network

it is found that both the topology of interface network and the grain size distribution present a strong fractal feature. There exists a close correlation between macro fracture energy and the fractal dimensions

in which the fracture energy increases with the increase of the fractal dimension. The relationship between fracture energy and fractal dimension of interface network can be well characterized by the quadratic function

while the relationship between fracture energy and fractal dimension of grain size distribution can be characterized by the linear function. The research results reveal a mesomechanism of macro fracture energy.