間隙水圧・変形連成問題への最近の取り組み 三軸圧縮破壊過程における岩石の透水性に封圧が及ぼす影響に関する研究

Abstract

The permeability of Kimachi sandstone in triaxial compression failure process was investigated by laboratory experiments. Tests were carried out under a constant confining pressure of between 5.0 and 15.0 MPa with a constant pore pressure of 2.0 MPa until axial strain reached approximately 5.0%. The stress-strain relation was linear under low differential stress and gradually became nonlinear as peak differential stress approached. In the tests under confining pressure of 5.0 and 7.5 MPa, the permeability decreased in the elastic region and then increased as the peak strength approached. The permeability continued to increase at first in residual strength region, and then it decreased at axial strain of approximately 4.0%. In the tests conducted under higher confining pressure, the variation in the permeability was small until axial strain of 5.0%. It appeared that failure types were different depending on confining pressure from the observation of the thin sections made from the specimens after tests. In the tests under 5.0 MPa confining pressure, a macroscopic fault occurred in the test pieces. On the other hand it did not occur in the tests under higher confining pressures. It was suggested in the elastic FEM analyses that the failure types were influenced by the end constraint.