Effects of construction sequence and pace on the stability of high embankments founded on soft marine clay

The construction of high embankments in regions where the soils are predominantly soft and consist of marine clay deposits with low shear strength poses special challenges. Due to the high water content of marine clay deposits, an increase in applied stresses results in excess pore water pressures and a consequent reduction in shear strength. The sequence, pace, and duration of embankment construction play an important role in determining the stability of high embankments built on these soft soils. In this paper, the effects of these parameters on embankment performance are examined by utilizing a case study of an embankment failure which occurred in 2006 during the construction of a four-lane highway leading to the Canada-USA border crossing in St Stephen, New Brunswick, Canada. The St. Stephen highway embankment, with a design height of 14 m, failed at a height of approximately 12.3 m. The problem under consideration is modelled by using finite element analyses with the PLAXIS 2D software. Modelling is carried out with a staged construction technique, where the pace of embankment construction depends on the thickness of the fill layer added at each construction stage, and the time allowed for consolidation following the addition of each layer. Fill layer thicknesses ranging from 0.6 m to 7 m are used, in combination with consolidation times ranging from 1 to 64 days. The results obtained show that the stability of embankments founded on soft soil deposits increases as the pace of construction decreases and as the time allowed for consolidation increases.