The physical and numerical modelling of fracture growth in underground excavations.

[摘要] In the field of numerical modelling in rock mechanics, one ofthe main hindrances is thelimited knowledge ofthe mechanisms of fracturing and failure in brittle rock. A way toincrease this knowledge of rock behaviour is by carrying out laboratory experimentsunder controlled conditions.The Displacement Discontinuity Method, capable of fracture growth simulation (DIGS),has been used to model fracturing of deep level underground excavations. In addition toan ordinary underground mining simulation, certain geological structures have beensimulated and there influence on fracturing. The main objective of this dissertation is toverify and calibrate DIGS by comparing results of physical experiments and numericalsimulations.Comparing the results of the laboratory experiments and the numerical simulations ofthese simulations, it has been possible to define the basic failure mechanisms around adeep level stope, and the influence of certain geological structures. The samples used todo the simulations were machined out of Quartzite, Black Reef Quartzite and Norite. Thetests were carried out in a biaxial cell, which was built especially for these tests.When mining in a solid block with no geological structures present, the effect of stopeclosure caused very different fracture formations when compared with the no stopeclosure case. When closure of the stope occurred, the fracture s formed ahead of the faceand shear fractures were formed. When closure of the stope did not take place, thefractures formed behind the face and the nature of the fractures were mainly tensile.DIGS correctly simulated the same fracture pattern as was found in the physicalexperiments.When simulating the effect of a discontinuity was carried out, fracturing tended to extendinto the discontinuity, but not through the discontinuity. Evidence of activation ofthediscontinuity was found. Simulating the effect of parting planes on fracture formation ledto the initiation of tensile fractures ahead of the face at the parting planes interface. Theseresults were obtained in both physical and numerical simulations.The comparison between the physical experiments and the numerical simulations hasshown favourable results indicating that DIGS can correctly simulate fracture initiation,fracture growth, stress conditions and stress redistribution.

[发布机构] University of the Witwatersrand