Influence of Geosynthetic Stiffness on Deterministic and Probabilistic Analyses of Reinforced Soil Structures with Focus on Reinforced Fills Over a Void
Mahdavi Naftchali, Fahimeh
Geosynthetics, Rate-dependent stiffness, mechanically stabilized earth (MSE) walls, Reinforced fill, Void, Arching, Limit states, Deterministic analysis, Probabilistic analysis, Factor of safety, Deformation, Strain, Tensile strength, Stiffness, Reliability index, Probability of failure, Level of understanding, Model bias, Isochronous load-strain behaviour, Creep, Hyperbolic stiffness model, Numerical modelling, finite difference model (FDM)
Geosynthetic reinforcement products are rate-dependent polymeric materials meaning that they exhibit strain-, time- and temperature-dependent behaviour under load. In the vast majority of the geosynthetics literature, the load-strain-time properties of geosynthetic reinforcement materials are ignored in the analysis and design of geosynthetic reinforced soil structures under operational (serviceability) conditions such as mechanically stabilized earth (MSE) wall structures and reinforced fills over a void. One important outcome of this thesis is a large database of geosynthetic reinforcement properties for a wide range of products and product classifications with their rate-dependent behaviour described by a simple two-parameter hyperbolic isochronous model. This model is used to demonstrate the influence of reinforcement stiffness on the magnitude of MSE wall deformations and loads under operational conditions. However, the main focus of this thesis is to examine the influence of reinforcement stiffness on the reinforced fill over a void problem. Analytical methods for geosynthetic-reinforced fills over voids most often overlook the impact of geosynthetic reinforcement reduced stiffness due to creep during tensile loading. This thesis addresses this gap by introducing a reinforcement stiffness limit state for analysis and design of these systems together with the two-parameter hyperbolic isochronous load-strain model. A disadvantage of analytical solutions for the reinforced fill over a void problem is that the coupled effects of fill and reinforcement properties, and problem geometry are not considered. To overcome this deficiency, a 2D finite difference (FLAC) numerical model of the reinforced fill over a void is developed that implements the hyperbolic isochronous load-strain model for the reinforcement layer. This thesis shows how rate-dependent properties of polymeric reinforcement geosynthetics impact reinforcement tensile strains, load, and overall system performance. There is a movement in geotechnical engineering towards a probabilistic approach to performance-based design and quantification of limit state margins of safety in probabilistic terms. This thesis looks at margins of safety for selected limit states for the problem of a reinforced soil fill over a void from both a classical factor of safety point of view and, for the first time, from a reliability-based design (probabilistic) point of view.