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Abstract The reasonable and accurate evaluation of deep rock strength has great importance on forecasting and controlling rock bursts and other dynamic geological disasters during excavation. Aiming at the problems of rock sample damage induced by coring-induced unloading，the damage zones and extent of rock samples under different stress levels are studied through numerical simulation and field sampling and indoor experiments. The results of numerical simulation and the corediscing phenomenon both confirm that the stress relieving sampling scheme suggested in this paper is effective，which can reduce stress of the sampling area by about 30%；and make it possible to core rock sample under different stress levels in same place. According to the result of the compaterized tomography(CT) scanning of the rock samples obtained from tunnels of Jinping II hydropower station with a buried depth of 1 900 m，unloading-induced damage extent may exceed 50% of the whole section of rock samples. The average uniaxial strengths of the rock samples by means of low stress sampling and over-coring increase by approximately 5% to 15% than conventional sampling under high stress condition and over-coring，with an average of about 8%；so the influence of coring-induced unloading damage on rock strength can?t be ignored. And the number of acoustic emission events of the former at early loading stage is significantly less than the latter，which indicates that the coring-induced unloading damage can?t be eliminated completely even by over-coring；and this result is in accordance with that of CT scanning.
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Received: 02 November 2012
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2013, Vol. 32 
