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Abstract The four-grade uniaxial cyclic loading and unloading tests for two groups of red argillaceous siltstones were carried out on MTS815 Flex Test GT rock mechanics test system. The sine wave is adopted in loading test，and its frequency was 3 Hz. The maximum cyclic stress was less than the value of the average intensity of compression；and the cyclic number of each level cyclic stress was 30. Through the test，the relationships of dynamic moduli of elasticity and damping ratio to dynamic strain for the two groups of rocks were gained. The test results showed that the curves of strain and stress for loading and unloading were not superposition under cyclic loading，but hysteresis loops. The strain wave location was always later than stress wave location；and the hysteresis loops were not ellipse-shaped，but tine-lobation when the cyclic loading was reversed. The dynamic strain increased with the increase of oscillation amplitude；the dynamic modules of elasticity was linearly decreasing with the dynamic strain increasing，but the damping ratio was reversed. The four relationship equations were gained，and the correlation coefficient R2 was over 0.98. Moreover，the irreversible plastic deformation of rock increased，and at the same time，the fracture deformation of rock gradually increased，which was produced by cyclic load.
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Received: 28 October 2007
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