The behaviour of reinforced and unreinforced embankments on rate-sensitive clayey foundations

Simplified design methods for reinforced embankments constructed on soft clayey foundations are advanced. A conventional elastoplastic finite element model is used to develop an approximate procedure for estimating the reinforcement strain at failure for geosynthetic reinforced embankments constructed on nonhomogeneous clayey foundation soils.;In 1989, geotextile reinforced test embankment was constructed to failure on a soft clayey silt deposit with some organics at Sackville, New Brunswick, Canada. A laboratory investigation into the rate sensitive behaviour of the Sackville foundation soil at yield is described and the ability of the two elasto-viscoplastic yield surface models, coupled with Biot consolidation theory, to describe the rate sensitive behaviour of the Sackville foundation soil is studied. The construction of the Sackville test embankment is then numerically simulated using an elasto-viscoplastic Elliptical cap model. The calculated behaviour is compared with the field performance and the comparison shows that a single elasto-viscoplastic yield surface model can adequately describe much of the measured time dependent behaviour of the Sackville test embankment.;Stages 1 and 2 of an unreinforced test embankment were constructed and subsequently monitored at Canadian Armed Forces Base Gloucester, Ontario, Canada. The rate sensitive characteristics of the Gloucester foundation soil during conventional laboratory tests are studied using two elasto-viscoplastic yield surface models. Stages 1 and 2 of the Gloucester test embankment are modelled using the elasto-viscoplastic Elliptical cap constitutive equation and the comparison of calculated and measured behaviour indicates that both the field and laboratory response of the Gloucester foundation soil during drained and undrained loading conditions can be adequately described. Furthermore, the consequences of adopting an alternative yield surface (e.g. Original Cam-clay) for the Gloucester foundation soil is also demonstrated.;Current design methods for reinforced embankments on soft cohesive foundation soils are evaluated using elasto-viscoplastic and elastoplastic finite element models. The use of Bjerrum's correction for the Sackville foundation soil is shown to be unconservative and an alternative approach for correcting field vane shear strength and cone penetration test results based on strain rate considerations is proposed.