ABSTRACT: This paper investigates the time-dependent swelling-softening process in clay shale around a drilled hole subject to fresh water invasion. A specially designed triaxial cell was fabricated for the purpose of this study. Computer tomography scanning was used to examine the deformation of the hole during swelling. In addition, the amount of sodium chlorine ions released from the shale specimen into the water was continually monitored. The test results show that the swelling-softening process is a mechanical-hydraulic-chemical coupled process. A new mathematical framework is developed and proposed for borehole stability analysis. Governing equations involving equilibrium and mass balances for fluid and ions must be included in the analysis. Constitutive relations describing modulus reduction due to swelling must be also taken into account.

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