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Abstract Triaxial unloading creep tests with alternatively distributed soft and hard rock specimen from auxiliary traffic tunnel of Jinping II hydropower station are carried out by the rock servo-controlled rheological testing machine. The creep laws of axial and lateral deformations under unloading confining pressure are obtained. According to creep test results，axial and lateral deformations are both unchangeable under high confining pressure with time；and the creep phenomenon of rock specimen is not obvious. As confining pressure decreases gradually，the specimen creep deformations become more and more prominent，and the typical creep three stages of rock appear；and the specimen creep deformations increase nonlinearly until the specimen damages. The creep rupture form of rock specimen is mainly shear failure and with a certain degree of tension damage；and the angle between failure plane and level is 45°roughly. Shear rapture surface is relatively single and smooth；and the evolution process of failure surface is along green schist bedding with lower strength and parallel to bedding plane. Before the accelerated creep stage，lateral creep deformation of rock specimen is smaller than axial creep deformation，while in the accelerated creep stage，lateral creep deformation and creep rate are both higher than those of axial creep，which suggest that the lateral creep deformation is more sensitive than axial creep deformation，and the specimen volume dilatation effect is remarkable with time and the decreasing confining pressure. In the condition of unloading，when the applied load is less than the long-term strength of rock specimen，the rock unloading creep parameters are related with unloading quantity，they are gradually weakening with the increase of unloading quantity；but when the applied load exceeds the long-term strength of rock specimen，the rock unloading creep parameters are related with both unloading quantity and creep time.
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Received: 03 June 2011
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2012, Vol. 31 
