关键词: 岩土工程, 石灰岩, 损伤, 分形几何学, 细观尺度

Abstract: The stress-strain time series and rock damage experimental fractures were obtained by laboratory uni-axial and tri-axial compressing experiments on limestone. The experimental fractures with the compressive failure of different confining pressures were analyzed by scanning electron microscope imaging experiment. Fractal dimensions in mesoscale space of limestone fractures were calculated to trace the damage feature quantitatively. The general rule that when the confining pressure increases (< 20 MPa), the compressive failure process inclines to be complicated and the fractal dimensions of limestone factures increase was obtained. When the confining pressure increased to about 2/3 uni-axial compressive strength of rock, latter compressing process may be controlled by new radial damage caused by high surrounding pressure, which resulted in that the final failure cause tended to be simple and the fractal dimensions of rock damage factures tended to be the minimum. The fractal dimension reduction index was introduced into the basic relation of continuum damage mechanics, and a fractal damage statistical model describing mesoscale failure mechanism of limestone was established. Comparing with the stress-strain test results, it is indicated that the fractal damage theory model is fitted with the experimental relation curve and can ideally reflect the strain softening feature of limestone tri-axial compression test. The proposed model is a valuable discussion for mesoscale failure mechanism of the damaged rock.

Key words: geotechnical engineering, limestone, damage, fractal geometry, mesoscale