Design of Geosynthetic Reinforcement for Embankments on Soft Soil Considering the Strength Increase of Foundation Soil due to Consolidation
Geosynthetics as reinforcement of embankments on soft soil are generally designed considering the end of construction solicitation and the final instant of the reinforcement service, taking into account the strength decrease due to creep. This loss is gradual in time; also, the resistance of the foundation soil changes in time due to the consolidation process. This paper discusses some of the considerations that one could adopt to analyse the stability of a reinforced embankment on soft soil, by considering time as a design parameter. It is presented, in order to illustrate, some results of an idealised procedure of analysis to take these aspects into account. Limit Equilibrium analysis are performed and compared to Finite Element results. Terzaghi's consolidation theory is the basis for the consolidation analysis; some hypothesis and limitations are discussed.
From the analysis performed and the results presented (for a chosen example), some conclusions may be undertaken:
− About the consolidation process: Terzaghi's Theory underestimated consolidation time for the example analysed, but it is on the safe side and it is a good tool on the collection of parameters to be input in stability analysis considering soil consolidation with consequent resistance increase;
− About the reinforcement creep: creep is very significant for polymeric products, mainly on the initial moments of loading; so, it should be always considered on reinforced embankments stability analyses;
− About general structure behaviour: even after consolidation (and consequent soil strength increase) has developed enough to ensure the embankment stability, reinforcement plays still an important role, by ensuring serviceability conditions to the structure; on this issue, the stiffness of the geosynthetic reinforcement is the parameter to be analysed and specified;
− About the stability analysis procedure suggested (idealized): there is no doubt that it is a less conservative analysis when compared to traditional ones, once it really takes the soil resistance increase into account and do not penalise in excess the reinforcement strength value in terms of decreasing due to creep susceptibility.