United States Department of Transportation
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Edition:Final Report
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Abstract:Experimental studies conducted over the course of the past 20 years have demonstrated both general and specific benefits of using geosynthetics as reinforcement materials in flexible pavements. Existing design solutions are largely empirically based and appear to be unable to account for many of the variables that influence the benefit derived from the reinforcement. Advanced numerical modeling techniques present an opportunity for providing insight into the mechanics of these systems and can assist with the formulation of simplified numerical methods that incorporate essential features needed to predict the behavior of these systems. Previous experimental work involving the construction of geosynthetic reinforced test sections has shown several difficulties and uncertainties associated with the definition of reinforcement benefit for a single cycle of load application. Even though many reinforcement mechanisms are apparent and often times striking during the application of the first load cycle, the distinction between reinforced test sections is not nearly so clear as that which is seen when examining long term performance, where long term performance is defined in terms of permanent surface deformation after many load cycles have been applied. This indicates the need for an advanced numerical model that is capable of describing the repeated load behavior of reinforced pavements. In particular, models for the various pavement layers are needed to allow for a description of the accumulation of permanent strain under repeated loads. To meet these needs, a finite element model of unreinforced and geosynthetic reinforced pavements was created. The material model for the asphalt concrete layer consisted of an elastic-perfectly plastic model where material property direction dependency could be added. This model allowed for the asphalt concrete layer to deform with the underlying base aggregate and subgrade layers as repeated pavement loads were applied. A bounding surface plasticity model was used for the base aggregate and subgrade layers. The model is well suited for the prediction of accumulated permanent strains under repeated loading and is most suitable for fine-grained materials. A material model containing components of elasticity, plasticity, creep and direction dependency was formulated for the geosynthetic and calibrated against a series of in-air tension tests. A Coulomb friction model was used to describe shear interaction between the base aggregate and the geosynthetic. The model is essentially an elastic-perfectly plastic model, allowing for specification of the shear interface stiffness and ultimate strength. This model was calibrated from a series of pull out tests. Finite element models were created to match the conditions in pavement test sections reported by Perkins (1999a). Membrane elements were used for the geosynthetic and a contact interface was used between the geosynthetic and the base course aggregate. Models of unreinforced and reinforced pavement sections were created and compared to test section results.
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Content Notes:Training materials can be accessed from: https://www.mdt.mt.gov/research/projects/grfp.shtml
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