EXPERIMENTAL STUDY ON CREEP PROPERTIES OF SOFT ROCK UNDER TRIAXIAL COMPRESSION

With the author-developed gravitation loading style rock creep test machine,under the conditions of constant temperature and constant humidity,triaxial compression creep experiments are conducted under different stress states.Oiliness mudstone samples are taken from Longkou Coalfields.The effects of confining pressure and creep parameters of soft rock were focused on;and other time-dependent behaviors were analyzed.The experimental results show that the stress threshold for the oil mudstone increases linearly with the confining pressure.The ultimate strength of creep is in direct proportion to confining pressure.The creep process of oil mudstone only goes through two phasest,hat is,one is in the damped creep phase when axial stress is less than the creep ultimate stress;and the other phase is accelerated when axial stress is larger than the creep ultimate stress.The even creep phase of oil mudstone is not observed in the test.The creep viscosity coefficient is become much smaller,which reveals the characteristics of large creep deformation.It is seen approximately as a linear function relation with the latter,but the viscosity coefficient increases slowly with the confining pressure.At the same time,the restriction of lower confining pressure to creep deformation is weaker.