Experiments on three-dimensional flaw dynamic evolution of transparent rock-like material under osmotic pressure

The dynamic evolution mechanism of intrinsic crack propagation in rocks is a topical and difficult problem in rock mechanics and engineering. Numerous examples of rock mass engineering disasters indicate that the three-dimensional (3D) flaw propagation and evolution process are the internal factors causing geological disasters. A persistent puzzle is the effect of osmotic pressure on the spatial form of crack propagation in compressed rock mass. As the naked eye cannot observe the dynamic evolution process of internal natural crack propagation, we experimented with transparent specimens that have brittle fracture properties similar to those of a rock-like material under frozen conditions. We prefabricated elliptical open cracks in the specimens, on which were applied osmotic pressure through a high-pressure osmotic injection equipment. Through uniaxial and biaxial compression tests, we established a set of compression test steps and methods for intrinsic open-type prefabricated crack specimens under osmotic pressure. Further, we analyzed and compared with the dynamic evolution law of the entire stress–strain process of 3D flaw under osmotic pressure, exploring the effects of different osmotic pressures and crack forms on the crack initiation, penetration, and peak strengths of elliptical open-type cracks. Consequently, the fan-shaped and spiral surface cracks formed by 3D flaw propagation were found for the first time without osmotic pressure. Meanwhile, osmotic pressure accelerated the growth of wrapping wing cracks and inhibited the growth of petal cracks and wrapping anti-wing cracks. Lateral pressure suppressed the vertical propagation of the wing cracks, increased the crack stress and peak strength, and reduced the initial propagation angle of the wing cracks at the long axis end of the prefabricated crack. These findings provide an important basis for expanding the initiation, propagation, evolution, and failure mechanism of 3D flaw under osmotic pressure in natural rock mass.