Pattern of coalescence of rock bridge between two joints under shear testing

This paper investigates the failure mechanisms and pattern of coalescence of modeling material containing two open joints under shear loads, with changing values of the joint length and the separation between the two joints along both horizontal and vertical directions. Both experimental and numerical studies show that the failure patterns of bridged rock are controlled by the separations between joints. In general, when horizontal separation is small and with non-zero vertical separation, tensile coalescence will dominate. If horizontal joint separation is greater, mixed mode coalescence (tensile plus shear) will dominate. In most of the cases only one crack grows actively and coalesces with the tip of other joint. However, for the joint separations within a critical range both upper and lower cracks initiate, coalesce and form a 'fish eye' mixed mode coalescence. Tensile crack is dominant throughout the failure process due to that the tensile strength of the material is lower than the shear strength.