顶板诱导致裂的数字探测及其分形特征研究

为观测采空区顶板诱导崩落的实施效果,研究采动影响与人工爆破强制诱导耦合作用下顶板岩体内节理、裂隙等不连续结构面的发育与矿岩破裂失稳崩落的关系,采用数字式全景钻孔摄像系统对顶板诱导崩落预裂钻孔进行了探测。探测结果表明,在实施预裂爆破钻孔内预裂缝从爆破点直至孔底,宽度达到20～40 mm,炮孔处理后至今顶板平均跨落厚度为30～40 m,诱导效果显著。岩体内以高陡倾角、窄隙宽和短隙长的次生裂隙群发育为主,微裂隙群的扩展、贯通最终导致岩体由顶板底部向上逐步剥离冒落。耦合扰动与单一采动扰动岩体内裂隙的发育情况差异明显。采用分形理论对不同钻孔同一深度的裂隙发育特征进行描述,得出不同诱导作用下岩体内裂隙数分维值及关系曲线。分析表明,诱导作用下岩体内的裂隙产生及其演化具有自相似性,其分维值随着诱导步距的推进不断增大。

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.