MULTIFRACTAL CHARACTERISTICS OF PORE STRUCTURE OF RED BEDS SOFT ROCK AT DIFFERENT SATURATIONS

The internal pores of red beds soft rock are random and diversified. Their changing characteristics can affect the macroscopic mechanical properties of the soft rock. The mesoscopic structure images of the rock samples at different saturation time are obtained by Scanning Electron Microscope and are used to calculate the fractal dimension by box dimension method. It is found that the fractal dimension of pores increases with the increase of saturation time. Basing on the quantity and size of pores,the distribution characteristics of pores in the rock samples at different saturation times are obtained. The multifractal theory is used to quantitatively evaluate pore structure. The results show that the distribution function of pore structure tends to be linear with q order,which verifies its self-similarity and scale-less property. The generalized fractal dimension of D(0)>D(1)>D(2) reveal the multifractal characteristics of pores,and the irregularity and complexity of pore structure are analyzed by multifractal spectrum parameters,which can characterize the distribution of different pore sizes. Combining the multifractal characteristics of pore structure with the compressive strength of the rock samples,the relationship between the change of pore structure and its mechanical properties is established,which has certain guiding significance for studying the damage process of the red beds soft rock.