Experimental study on creep of rocks under step loading of seepage pressure

The creep and damage of fine sandstone rock under gradual loading of seepage stress are investigated through a series of triaxial compression tests using RLW-2000M coal and rock computer-controlled rheological testing machine. The volumetric strain and seepage volume (volume rate) evolution curves of rock creep under different seepage stresses are highlighted. In addition, the transformation curves of rock creep and permeability coefficient under different seepage stresses are analyzed and compared. The results show that the porosity evolution has agreement with three stages in typical creep process. As the gradual loading of seepage water pressure, the instantaneous axial and transverse strains as well as Poisson's ratio have an increasing trend. With the accumulated strain, the transverse strain is greater than the axial one in company with expansion effect until the occurrence of creep damage. The seepage volume curve is linearly evolved under the gradual loading of seepage water pressure. It is conclued that the permeability coefficient decreases firstly and then increases. The initial permeability has a memory (a memory of rock pore channels) that pore channels are formed through the process of deformation-closing-erosion-new channel.