Study On The Rheologic Fracture Of Jointed Rock Mass Under Inducing Condition And Its Engineering Application

Block caving is a mining method with low cost and high efficiency. It is especially fit for the developing-jointed thick ore mass. In this method, the block is completely undercut into a free space with certain area and high at the bottom, which changes the stress distributions in rock mass. The man-made stress-induced manner urges the fracture and block of rock mass caving by itself weight. However, the caving maybe happen because of too large transmogrification and rheologic fracture to high crustal stress and cracked rock mass. The fracture mode is different from that of the hard and brittle rock mass under secondary stress field. At present, the body of theoretical and practical knowledge of the factors controlling the caving process is limited, and the economic risk and technological difficulties in developing a caving mine can therefore be higher than one would like. To remedy this situation, the author studied deeply and systematically on the rheologic fracture problems of jointed rocks under inducing conditions, combining with the two projects: the key technologies R&D project supported by the nonferrous metals company of Jinchuan 'Study on block caving law of the cracked ore rocks under the conditions of high crustal stress', and the innovated project of PHD candidate supported by Central South University 'Study on block caving mechanisms for flabby and intricate rock mass under inducing conditions (134375210)'. The main contents of the dissertation are summarized as follows:The summarized mechanical model of single crack applied by the remote stresses was built, based on the theory of fracture mechanics and some assumes of cracked configuration in space. Whereafter, the summarized model was continuated from single crack to several-set cracks through importing the network of beams method. And some equations were derived to calculate stress intensity factor at the wing crack tip.The double-torsion load-relaxation method at constant displacement was adopted, and three kinds of rocks coming from Jinchuan mine were tested to get the parameters of subcritical crack growth (SCG) and fracture toughness using the INSTRON 1342 type electro-hydraulic servo testing machine. The relations between stress intensity factor and subcritical crack growth velocity were analysed, the threshold value of...