Permeability and Deformation Characteristics of Shirahama Sandstone under a General Stress State

Permeability and Deformation Characteristics of Shirahama Sandstone under a General Stress State Author: M. Takahashi In this paper, results of experimental studies on the dependence between the permeability and the deformation mode of Shirahama sandstone subjected to an axi-symmetric triaxial compressive stress state and a true triaxial compressive stress state are presented. Under conventional triaxial compression conditions, in the brittle faulting regime, permeability decreases with increasing axial strain until the onset of dilatancy when it increases signifi cantly with ongoing axial strain. For specimens subjected to effective confi ning pressures of less than 10 MPa, the fi nal permeability is greater than the initial value; by contrast, in both the brittle–ductile transition and ductile regimes the permeability following the onset of dilatancy increases only slightly. Deformed and failed specimens show a fi nal value of permeability that is lower than the initial pre-deformation value. Whether shear displacement exerts a signifi cant control on the permeability of faults in rock masses is a major topic of concern in the fi elds of engineering and earth sciences. To clarify the relation between permeability and the internal structure of a rock sample, the three principal strains and permeability along the intermediate principal stress direction were measured during deformation as a function of the three principal stresses. The specimen was deformed under a true triaxial compression stress state in which the intermediate principal stress was different to the minimum and maximum principal stress.

 

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