Oedometer tests were conducted on dry and saturated kaolinite clay samples to investigate the effects of stress level, stress history, pore fluid type, and drainage path on time-dependent deformation under one-dimensional (1D) constant stress. Different deformation modes involved in the creep compression were identified and quantified: creep deformation of individual particles and creep shear displacement at particle contacts. It was found that the creep compression is a coupled process involving the above creep deformations and induced viscous flow resulting in pore compression. The rate of 1D creep compression is controlled by the drainage path along which the viscous flow occurs. It was also observed that mechanically induced consolidation has an accelerating effect on the creep compression of the test samples existing within the limit time zone. This observation confirms that 1D creep compression is a continuation of 1D consolidation in which the largest existing interaggregate pores collapse under a given effective stress. No creep compression was observed when the test samples were mechanically overconsolidated to a state beyond the limit time zone because the interaggregates were compressed to a stable structure. Reduced creep compression was detected in chemically induced consolidated samples though their states were beyond the limit time line.

Bentonite seams of varying thicknesses, from a few millimetres to about 30 cm, are found at depths of 200-300 m within the Belle Fourche Formation and Second White Specks unit in the Cretaceous Colorado Group in the Cold Lake area of Alberta, which is one of four exploration sites for extraction of heavy oil in Alberta. Thermal heavy oil recovery processes in oil sand reservoirs, such as cyclic steam stimulation and steam-assisted gravity drainage, cause casing impairment and failure in the overlying Colorado Group shales. Based on the results from triaxial compression and direct shear box tests on bentonite seam samples, the material displays not only low stiffness and friction angle, but also pronounced creep. Results from numerical analyses of case studies illustrate that the shear slip mechanism along these bentonite seams is admissible in the field under steam stimulation processes. The slip mechanism is mainly attributed to the huge contrast in deformation moduli and creep between the soft bentonite seam and the stiff Colorado Group shales, rather than due to the low frictional resistance derived from the bentonite seam.