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Numerical analysis of reinforcement strains at failure for reinforced embankments over soft soils

Resumo

The use of geosynthetics as basal reinforcement in embankments constructed over soft soils provides technical and economic benefits by improving the stability of the structure, reducing horizontal displacements, homogenizing differential settlements, and reducing time of construction. An adequate design should include, however, more than routine limit equilibrium analyses, and should focus on understanding the soil-reinforcement interaction and mobilization of reinforcement strains during construction and with time, aspects that can be assessed with the use of finite elements simulations. This article presents the results of finite elements simulations for a hypothetical embankment over soft soil, applying the conceptual framework developed by Rowe&Soderman (1987), Rowe et al. (1995) and Hinchberger&Rowe (2003). Two approximate methods for obtaining the reinforcement allowable compatible strain at failure without the need for numerical simulations also are compared and discussed. The results in this article highlight the importance of assessing the mobilization of reinforcement strains during construction and taking into account soil-reinforcement interaction, given that reinforcement strains must be compatible with the soil system. An important implication, often overlooked in the past, is that the specification of geosynthetic materials for this application should be based on a minimum reinforcement stiffness modulus, i.e., the ultimate strength of the material may not suffice as a specification parameter.

Conclusão

Limit equilibrium analyses of the overall stability of reinforced embankments over soft soil can provide an estimate for a required reinforcement force for satisfactory factor of safety. However, an understanding of the soil-reinforcement interaction and mobilization of reinforcement strains during construction is critical for the correct definition of the geosynthetic reinforcement to employ. For a hypothetic embankment over soft soil considered in this study, the net embankment height, point of contiguous plasticity and reinforcement allowable compatible strain were studied following a previously defined theory. In addition, approximate methods for predicting the allowable compatible strain without the need for numerical simulations were verified, and one of the procedures overestimated the strain by 15%, whereas the other underestimated the strain by 35%. Finally, this article discussed the fact that the specification of geosynthetic materials for this application should be based on a minimum reinforcement stiffness modulus, instead of solely the ultimate strength of the material.