Experimental Study Of Rock Brizilian Disk Test Under Coupled Static-Dynamic Loads

Due to the shortage of experimental and theoretical research on rock mechanics in deep engineering, experiments using the Brazilian disk specimen were carried out in an innovative split Hopkinson pressure bar (SHPB) apparatus which was constructed considering the particular stress state of rock with static-dynamical coupling loads. In order to serve for the disaster prediction, accidents prevention, design and construction in the deep rock engineering, it is necessary that a completed Brazilian test system of rock under static-dynamical coupling loads is constructed and the the special law of the rock tensile strength in deep is obtained. Hence, the main works in this paper conclude the following aspects:(1) Specification of the test equipment. To avoid inherent defects of the conventional rectangular loading waveform such as strong oscillation, too short rising time, which may lead the invalidation of the dynamic Brazilian disk test (confirmed by our tests), half-sine wave loading achieved by SHPB test device with a shaped striker is used in the experiment. To ensure the accuracy of the measured data in the test, based on the analysis of the specific stress wave propagation features of the device, standardized calibration procedures before test were proposed and applied in this experiment.(2) Verification of the test effectiveness. From the basic principle of Brazilian test, the three key issues determing the effectiveness of tests under static-dynamic coupling loads (including pure dynamic load) were analyzed:stress equilibrium at the ends of the specimen; stress distribution within the sample before the destruction of the sample; specimen failure mode. Studies of these three issues were deeply carried on one by one with the help of various theoretical and experimental means, and the test effectiveness was fully verified.(3) Studies on the tensile characteristics of rock under static-dynamic coupling loads. A method for determining the tensile strength of the disc with static-dynamic coupling loads was proposed; rock fracture mechanism and strain rate effect were revealed by the observation and analysis of the specimen dynamic response and failure process under static-dynamic coupling loads. The tensile strength regulation of the measured granite under different coupling loads was obtained. The conclusion could be used as an supplement to the current deep rock mechanism.The innovations of this paper include:(1) Studies on the tension damage of rock under the particular static-dynamic coupling loads and examinations of the mechanism and process of rock failure under the multiple stress field. Because the state of stress in specimen is appromaximated that in deep rock, the results could be applied for deep engineering better; (2) A method proposed to determine the rock tensile strength under static-dynamic coupling loads in the Brazilian disk test and the relevant strength regulation obtained, which could provide a reference for explanating, predicting, and controling the tensile damage of rock in deep engineering, suck as zonal disintegration, slabbing, rock burst.