ROCKBURST - Devastating micro cracks: researching spontaneous rock failure with rock mechanical testing, μCT, OBIA and geostatistics

Predicting the behavior of rock mass is of paramount importance in tunneling and mining, as well as in earthquake prediction and geothermal energy utilization. Only if the cracking processes in rock are wellunderstood, failure can be foreseen and avoided. Brittle failure is particularly problematic, as the rock fails abruptly with practically no prior warning. Laboratory tests and observations in deep tunnels and mines with large overburden have shown that certain rock types exhibit a high potential to store elastic energy and therefore are prone to sudden, violent failure. In literature, only general descriptions of brittle failure mode and cracking process in brittle rock are available. Profound knowledge on the underlying mechanisms is still missing, however. No systematic laboratory investigation on the microstructure’s influence has been provided so far. This proposal presents a multidisciplinary approach to research the influence of micromechanical and microstructural characteristics and their individual effect on rock failure. Stateofthe art rock mechanical testing, data acquisition and simulation methods will be nested in an innovative workflow: Following initial mineralogical investigations, artificial and natural rock samples will be each be subject to cycles of destructionfree microstructure analysis and compression testing. From each cycle, Microcomputed tomography (μCT) will provide 3D data on the sample’s microfabric before a successive step of uniaxial testing controlled by acoustic emission testing is carried out. From the resulting series of μCT data, Objectbased Image Analysis (OBIA) will assemble a process (3D+t) model of microcrack evolution in each sample. Multiplepoint geostatistics simulation, based on training images provided by OBIA, will be used to upscale OBIA results from sample scale to excavation scale. The research is carried out by an international team of acknowledged experts; we expect completely new insights into relevant micromechanical processes in highlystressed brittle rock and their quantitative comprehension. Potential results are considered a mandatory basis for further developments to minimize risks in deep underground mining and construction, as well as for improving the prediction quality for seismic events in the process of hydrofracturing.