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Abstract According to borehole cores with the length more than 1 500 m in deep tunnels at Jinping II hydropower station，the information of the macro-damaged characteristics，quantity and thickness distribution of discing core were collected and the spatial distribution of core discing was analyzed. Then，the influences of different buried depths，geologic structure，tunnel geometric size，drilling diameter and directions on core discing were studied in combination with the results of elastic wave test and digital borehole images. Simultaneously，by applying scanning electron microscope technique for discs? surface，the micro-damage mechanism was discussed. The results indicated that：(1) The relationship between the quantity and thickness distribution was similar to a power function form. The quantity of core discing increased with depth and tunnel dimension. Within the zone of 3 times of tunnel diameter，core discing occurred more frequently. (2) The convex-concave formation was related to stress distribution，internal damage and mineral structure types. (3) Core discing often occurred under the joint action of geological and external effects. The native micro defects，structural plane and external disturbance were the discing foundation；the local stress concentration and stress release were the power of discing；the continuous drilling was the intrinsic cause of core broken into pies；the radial cut-compressive，axial tensile stress and lateral expansion of rock cores were the mechanical response of rock mass fracture. (4) Discing zone characteristics were the comprehensive reflection of rock damage weakening，rock mass structure and local stress concentration.
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Received: 15 April 2011
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2011, Vol. 30 
