Stabilization of very soft soils using high strength geosynthetics: the role of finite element analyses

Abstract

The application of finite element (FE) techniques for the analysis of reinforced embankment behaviour is reviewed. Details such as the choice of finite element and constitutive models as well as the validation of finite element results against benchmark solutions are discussed. Results from the authors' finite element analyses are examined, and it is shown that FE analysis can be particularly useful for identifying the mechanisms of failure and also for indicating why a geosynthetic reinforcing material may substantially improve stability for a certain foundation strength profile whereas for different foundation strength profiles the same reinforcement may give rise to negligible improvement in embankment stability. The use of plasticity solutions for estimating the maximum effect of reinforcement is illustrated. The results of finite element analyses are then used to demonstrate that although the collapse load calculated from plasticity theory can be attained for very highly reinforced embankments, in many situations failure will occur at embankment heights well below the collapse height. It is then demonstrated that the failure height for a reinforced embankment is related to the modulus of the reinforcement but is not very sensitive to the modulus of the soil. The development of strain in the geotextile is examined and it is demonstrated both from field evidence and theoretical analysis that the reinforcement plays a relatively small role at low load levels since the soil is essentially elastic. Significant strain in the geotextile begins to develop with increasing plasticity and in fact most of the strain is developed after a contiguous plastic region is developed in the soil, since beyond this point the reinforcement is all that prevents collapse from occurring. As a consequence, the strains developed in reinforcement for a given embankment height will largely depend on the height of the embankment relative to the height at which contiguous plasticity occurs, and hence will be sensitive to the magnitude and distribution of the actual shear strength in a soil deposit.