About Some Problems Related to Determination of the E.G. Biot Coefficient for Rocks

Abstract

use of the poroelasticity theory by Biot in the description of rock behaviour requires the value of the e.g. Biot coefficient α to be determined. The α coefficient is a function of two moduli of compressibility: the modulus of compressibility of the rock skeleton K s and the effective modulus of compressibility K . These moduli are determined directly on the basis of rock compressibility curves obtained during compression of a rock sample using hydrostatic pressure. There is also a concept suggesting that these compressibility moduli might be determined on the basis of results of the uniaxial compression test using the fact that, in the case of an elastic, homogeneous and isotropic material, the modulus of compressibility of a material is a function of its Young modulus and its Poisson ratio. This work compares the results obtained from determination of the Biot coefficient by means of results of compressibility test and uniaxial compression test. it was shown that the uniaxial compression test results are generally unsuitable to determine the value of the coefficient α . An analysis of values of the determined moduli of compressibility shows that whereas the values of effective moduli of compressibility obtained using both ways may be considered as satisfactorily comparable, values of the relevant rock skeleton moduli of compressibility differ significantly.