Digital detection and fractal characteristics of induced fracturing of roofs

In order to measure the results of induced caving of roofs in mined stopes and to study the relationship between the rock failure and the development of discontinuities such as joints and fractals,which propagated under the coupling action by mining excavation and forcibly induced man-made blasting,the digital panoramic borehole camera technology was used to inspect the pre-splitting holes in roofs.It was shown that the effect of induced caving was prominent.Pre-cracks of 20 to 40 mm width in pre-splitting holes after blasting extended to the bottom of holes.The average failure thickness of roofs reached 30 to 40 m.Steep obliquity,narrow width and short trace length were the main characteristics of fractures in rock mass.Developing fractures formed the fracture net and led to the spalling of rock from the bottom to the top of roofs because of their propagation and coalescence.The developing conditions of fractures in rock mass operated by the coupling jamming and the single mining excavation were different.The characteristics of fracture development at the same location in different boreholes were studied by using the fractal theory.According to the research results,fracture values under different disturbances were calculated and their relationship curves were drawn.It was found that the evolvement under disturbance was self-similar and its value became larger and larger along with the process of induced caving.