Behaviour of Three Test Embankments Taken to Failure on Soft Clay

Abstract

This article compares and analyses the behaviour of three test embankments. The soil foundation consisted of normally consolidated clay overlain by a thick sand surface layer. The embankments were rapidly constructed until failure, which occurred after approximately 50 days. Two of the embankments were reinforced, one including prefabricated vertical drains (PVD), while the third had neither reinforcement nor PVDs. The two reinforced embankments presented similar net embankment heights (fill thickness minus average settlement) at failure, owing to the similarity in the undrained strength values of the two clay layers. The test embankment with PVDs showed that this drainage feature improved overall behaviour but the benefit was less than suggested in the literature, owing to the low coefficient of consolidation of the normally consolidated clay, rapid construction and drain disturbance effects. Numerical analyses of the test embankment with PVDs showed good overall agreement between measured and computed values and confirmed overall field observations. The embankment without reinforcement and PVDs reached a greater embankment height than the two reinforced embankments, owing to its greater clay strength.