Characterisation of rock fracturing ahead of the preconditioned mining faces in a hard rock mining

摘要

A study on the characterisation of rock fracturing ahead of the preconditioned mining faces in a hard rock mining is described. The study involves the use of borehole periscope, ground-penetrating radar (GPR), the concept of core disking and numerical modelling. The results of the study have shown that extension fractures are firstly developed as groups, separated with solid zones, and as time progresses, the grouping of the fractures disappeared. In supporting the above findings, extension fractures were noted to be developed in a manner of micro-fractures, close fractures to open fractures as time progress. However, open fractures were observed to be developed quicker closer to the borehole core as compared with several metres within the tunnel front. In the meantime, GPR results correspond very well with the borehole periscope observations, by revealing the maturity of fracture as time progresses. In supporting the periscope observation and GPR, the recovered cores have shown a variety of core disking with the decrease in core thickness as the depth increases. The numerical simulation revealed a gradual closure at the vicinity of the borehole with extensive closure taking place along the sidewall of the borehole. The study concluded that the initiation of extension fractures was not limited to a certain depth; it was observed and validated to depend on the rate at which the rock mass deteriorates, which is mostly controlled by the rock mass properties.