Chapter 27 Case histories of embankments on soft soils and stabilisation with geosynthetics: Canadian experience

Abstract

The behaviours of Hall's Creek test embankment constructed on an alluvium deposit in Moncton, New Brunswick, and the reinforced test embankment constructed on a soft compressible soil in Sackville, New Brunswick, where a high-strength polyester woven geotextile was used as basal reinforcement are discussed in this chapter. The soils at both these sites have the same geological depositional history. Performance monitoring included the instrumentation of the foundation soil with inclinometers, pneumatic piezometers, settlement plates, settlement augers and heave plates and the geosynthetic reinforcement with different types of strain gauges. Details of the layout, instrumentation, field performance and analyses for behaviour prediction are presented. The observed settlement response of the Hall's Creek embankment could be predicted satisfactorily using Bjerrum's consolidation plus delayed compression approach by considering the immediate, primary and secondary compression; the unusually high pore water pressures that existed even after a 3-year period could not be explained adequately. From further laboratory investigation coupled with the pore pressure and settlement responses, it was concluded that progressive failure of the foundation soil could have been a contributory factor for the observed behaviour. The predictability of the behaviour of the Sackville reinforced embankment under working stress conditions using three types of fully coupled finite element analysis models; namely, a rate-formulated elasto-viscoplastic model with an elliptical cap yield surface, a creep-formulated elasto-viscoplastic model and modified cam clay (MCC) elastoplastic material model for the foundation soil is examined in this chapter. This study suggests that all three FEA models are capable of predicting the performance of this reinforced embankment under working stress conditions reasonably well despite their inability to give accurate predictions of all the behaviour characteristics. The analysis with the creep model gave slightly better overall predictions and that with the rate model predicted the horizontal displacement near the embankment toe and excess pore pressure in the foundation soil better than the MCC model. However, the creep and rate models require additional soil parameters and consume much larger computing resources and longer time. The MCC model could be adequate for predicting the performance of embankments on Sackville-type foundation soils under working stress conditions.