Pore pressure coefficient B for saturated geomaterials with compressible, isotropic and uniform solid and fluid phases

Abstract

This paper derives an expression for pore pressure coefficient $$B$$ in terms of a geomaterial’s mesoscopic properties and jacketed and unjacketed macroscopic compressibilities. The mesoscopic properties include phase compressibilities and pressure distribution ratios. The pressure distribution ratios represent the geomaterial’s meso-heterogeneity, while the difference between the unjacketed bulk compressibility and the solid grain compressibility represents macroscopic effects, such as solid grain rearrangement. The difference in phase compressibilities is shown to be the principal determinant of $$B$$ , with the effects of meso-heterogeneity and macroscopic change relatively negligible. The unjacketed pore compressibility appears to be quite sensitive to the effects of both meso-heterogeneity and macroscopic change. Although $$B$$ can be derived reliably from a measured value of unjacketed pore compressibility, unjacketed pore compressibility derived from a measured value of $$B$$ is considered unreliable. The expression for $$B$$ includes five elastic coefficients. The necessary and sufficient condition for constant porosity in an unjacketed test is proposed. The published expressions for $$B$$ , the coefficient of fluid content and porosity change are recovered by introducing appropriate assumptions with regard to meso-heterogeneity and phase compressibilities.