Full Sandstone Microcrack Damage Behavior Of Water Environment

Rocks contain numerous microcracks. The damage gradually develops with microcrack growth, and the rock material will fracture at last. The microcrack induced damage is an important material damage. Since pore pressure of water will drive the microcrack to grow, the influence of pore pressure should be considered when building damage model.Making use of MTS815 test system of rock mechanics, the uniaxial compression experiments and triaxial compression experiments with different confining pressure and water pore pressure are conducted. The experimental results show the compression strength of normal specimen is larger than that of saturated specimen, while their effective elastic module do not show any difference. The confining pressure will increase with compression strength of sandstone, while decrease with pore pressure.Considering the effect of pore pressure on microcrack growth, introduce the energy balance theory to describe microcrack growth, the opening deformation, frictional sliding, in plane-growth, kinked growth, and coalescence of elliptic microcrack are investigated, and a statistical damage model for water saturated sandstones is formulated. The triaxial compression tests of water saturated sandstone under different pore pressure are calculated by the proposed model, and the calculated results well describe the experimental results. The calculations of gas saturated coal show the proposed model can also be applied to gas saturated coal.The effect of microcrack interaction on rock deformation is researched. The FEA results show the effect of microcrack interaction can not be ignored when the parameter of microck distance is lower than 2. A micromechanics damage model which can describe the microcrack interaction and microcrack growth is formulated in Mori-Tanaka's scheme. The theoretical results show the effect of microcrack interaction should be considered if the parameter of microck distance is lower than 2, while that can be ignored if the parameter of microck distance is larger than 3.