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HYDRATION SWELLING OF WATER‐ABSORBING ROCKS: A CONSTITUTIVE MODEL
Author(s) -
HEIDUG W. K.,
WONG S.W.
Publication year - 1996
Publication title -
international journal for numerical and analytical methods in geomechanics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.419
H-Index - 91
eISSN - 1096-9853
pISSN - 0363-9061
DOI - 10.1002/(sici)1096-9853(199606)20:6<403::aid-nag832>3.0.co;2-7
Subject(s) - swelling , oil shale , geotechnical engineering , geology , constitutive equation , poromechanics , creep , mineralogy , porosity , finite element method , porous medium , thermodynamics , materials science , composite material , paleontology , physics
Water‐absorbing rocks are formed from minerals that can hold water in their crystal structure or between grain boundaries. Such water absorption is often accompanied by a change in the crystal dimension that manifests itself as a swelling of the rock. Swelling is particularly pronounced in rocks containing phyllosilicates because of the ease with which these minerals hydrate; it is thus of geological and geotechnical relevance in shales, clay‐rich soils and zeolitized tuffs. The model of hydration swelling that we present here is based on extended versions of the equations of poroelasticity and Darcy's transport law, which we derive using a non‐equilibrium thermodynamics approach. Our equations account for the hydration reaction under the assumption that the reaction rate is fast in comparison with the rate at which hydraulic state changes are communicated through the rock, i.e. that local physico‐chemical equilibrium persists. Using a finite‐element scheme for solving numerically the governing equations of our model, we simulate the creep of shales during a routine swelling test and calculate the stress and strain distributions around wellbores drilled in shale formations that undergo swelling. We show that swelling effects promote tensile failure of the wellbore wall.