Viscous behaviour of clays in one-dimensional compression

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.