Viscosity and secondary consolidation in one-dimensional loading

Viscosity and secondary consolidation effects are observed in one-dimensional compression, but it remains unresolved if viscous effects occur during the primary consolidation phase and consequently whether the end of the primary consolidation (EOP) line is unique and the H-2 scaling law applies. Dynamical systems soil mechanics suggests that viscosity and secondary consolidation each have a separate physical basis. Viscous behaviour is due to strain rate dependence of the coefficients of friction at interparticle contacts as they slide against each other in simple friction, and occurs during both primary consolidation and secondary consolidation. Secondary consolidation is the continued deformation of the soil structure after excess pore pressure has dissipated, as small numbers of particles move at random shear strains, in a Poisson process, to new final positions. The near constant C-(alpha e)/C-c ratio is due to the form of the equation that expresses this ratio and because very few particles move to new positions during secondary consolidation. Strain rates for typical geotechnical problems being pseudo-static, viscous effects in the field are small, and the current design practice of using the EOP curve and C-(alpha e) to calculate compression settlements appears reasonable. Empirical evidence suggests that adsorbed water layers control strain-rate-related effects.