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Numerical modelers are often faced with the challenge to numerically reproduce the physical behavior of soil-geosynthetic interaction problems using assumed values for missing soil and interface model parameters. This paper examines two such examples using the finite-difference method, (1) horizontal pullout of a geosynthetic (geogrid) reinforcement layer in a pullout box and (2) a geosynthetic (geotextile)-reinforced soil layer over a void. It also presents the results of parametric sensitivity analyses for the missing soil and interface model parameter values and identifies the values that give the best agreement with measured data. The paper further demonstrates that correct modeling of geometrical nonlinearity is key to accurately predicting the performance of geosynthetic-reinforced soil systems controlled by the tensioned membrane effect. The lessons learned in this study will be of interest to numerical modelers during numerical model design of geosynthetic-reinforced soil systems. [ABSTRACT FROM AUTHOR]

The paper presents the numerical modelling details using the finite difference method (FDM) to simulate the performance of a well-instrumented geogrid-reinforced incremental concrete panel soil retaining wall. Two different constitutive models were investigated for the backfill soil (linear elastic-plastic model and nonlinear elastic-plastic model). Both constant stiffness and strain-dependent secant stiffness models were used for the reinforcement elements. The paper provides valuable lessons to modellers to simulate the performance of this type of earth retaining structure. For example, parametric investigation of the effect of a constant Young's modulus ranging from 40 to 120 MPa for the linear-elastic Mohr-Coulomb model had only minor influence on the wall facing displacements and reinforcement loads. However, the choice of magnitude of transient compaction pressure near the facing can result in large differences in facing displacements. The paper also demonstrates that the method of construction including the location, sequence, and stiffness of the temporary supports used to construct the wall plays an important role on measured and predicted wall performance. The physical measurements reported in this paper provide a benchmark for numerical modellers to verify other numerical models for walls of the type investigated here. [ABSTRACT FROM AUTHOR]

The paper reports numerical model details and predictions of the end-of-construction performance for two instrumented and well-documented mechanically stabilized earth (MSE) walls. The walls were constructed as part of the highway SR-18 approach fills for a bridge near Seattle, Washington. The geogrid reinforced block face walls were modeled using a commercially available two-dimensional (2D) finite-difference program. The paper provides details on how material properties were selected from laboratory testing of wall components and how the computer modeling was carried out. The paper shows that predicted wall deformations and reinforcement strains were in reasonable agreement with measured data using both linear elastic-plastic and nonlinear elastic-plastic constitutive models for the soil. The geogrid reinforcement was simulated using a nonlinear load-strain-time secant stiffness model and cable elements. The paper compares numerical predictions of reinforcement loads at end of construction with measured values and predictions using a AASHTO Simplified Method, K-stiffness Method, and Simplified Stiffness Method. The paper is a useful benchmark for modelers because it demonstrates what the authors believe are reasonable expectations of model accuracy for Class C predictions of deformations and reinforcement strains for these types of walls when high-quality project information is available. [ABSTRACT FROM AUTHOR]

This article describes a rate-dependent hyperbolic model that was developed to predict the tensile load-strain behavior of a polypropylene geogrid reinforcement material under monotonic and stepped constant rate-of-strain testing. A more general three-component model previously reported in the literature was also used in the current study but with some modifications to compute model parameters. Details of the trial and error procedure to select three-component model parameters, not previously reported in the literature, are explained. Both models gave similar good agreement between measured and predicted constant rate-of-strain tests. The accuracy of the three-component model to simulate stepped constant rate-of-strain tests was judged to be better, but for practical purposes, the simpler hyperbolic model was judged to be satisfactory. An advantage of the hyperbolic model is that the model parameters are easy to determine, only monotonic constant rate-of-strain tests are required, and numerical implementation is simple. However, the hyperbolic model is restricted to monotonic or stepped constant rate-of-strain load paths. An advantage of the more complicated three-component model is that it has been demonstrated in previous studies to be more general and thus can be used for other load paths and other polymeric reinforcement material types that do not have characteristic hyperbolic load-strain behavior. POLYM. ENG. SCI., 55:1617-1627, 2015. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The results of load and resistance factor design (LRFD) calibration are reported for the pullout limit state in geogrid reinforced soil walls under self-weight loading and permanent uniform surcharge. Bias statistics are used to account for the prediction accuracy of the underlying deterministic models for load and pullout capacity and the random variability in the input parameters. The paper shows that the current AASHTO simplified method to calculate reinforcement loads under operational conditions is overly conservative leading to poor prediction accuracy of the underlying deterministic model used in LRFD calibration. Refinements to the load and default pullout capacity models in the AASHTO and Federal Highway Administration guidance documents are proposed. These models generate reasonable resistance factors using a load factor of 1.35 and give a consistent probability of pullout failure of 1%. A comparison with the allowable stress design (ASD) past practice shows that the operational factors of safety using a reliability-based LRFD approach give factors of safety greater than 1.5. Regardless of the design approach (ASD or LRFD), the analysis results demonstrate that the current empirical minimum reinforcement length criteria will likely control the design for pullout. [ABSTRACT FROM AUTHOR]

Abstract: The paper examines the accuracy of two geogrid pullout capacity models used in Japan (Public Works Research Center-PWRC, 2000a) by comparing measured capacities from a large database of laboratory pullout tests to predicted capacities. One model is the current default model (Model 1) used when project-specific laboratory pullout testing is not available and the other when this data is available (Model 2). The accuracy of the models is quantified using bias statistics where bias is defined as the ratio of measured pullout capacity to predicted value. Bias statistics are also a necessary precursor for reliability-based load and resistance factor design calibration for the ultimate pullout limit state in the internal stability design of geogrid reinforced soil walls. Bias statistics using Model 2 show that pullout predictions are very accurate with negligible scatter. However, the default model is shown to be very conservative on average with large scatter in bias values which also varies with magnitude of predicted pullout capacity. A modified formulation for Model 1 is proposed that has the same number of empirical coefficients as the current expression (i.e. two). The modified formulation gives improved accuracy based on the computed mean and coefficient of variation of bias values, and eliminates the significant model bias that is present for the current model. A final outcome from analysis of all available pullout data is that a factor of safety F=2 is recommended for allowable stress design (ASD) when using the current PWRC default Model 1, and a value of F=1.25 is recommended when using Model 2 with project-specific pullout testing. [Copyright &y& Elsevier]

A numerical finite-difference method (FLAC) model was used to investigate the influence of constitutive soil model on predicted response of two full-scale reinforced soil walls during construction and surcharge loading. One wall was reinforced with a relatively extensible polymeric geogrid and the other with a relatively stiff welded wire mesh. The backfill sand was modeled using three different constitutive soil models varying as follows with respect to increasing complexity: linear elastic-plastic Mohr-Coulomb, modified Duncan-Chang hyperbolic model, and Lade’s single hardening model. Calculated results were compared against toe footing loads, foundation pressures, facing displacements, connection loads, and reinforcement strains. In general, predictions were within measurement accuracy for the end-of-construction and surcharge load levels corresponding to working stress conditions. However, the modified Duncan-Chang model which explicitly considers plane strain boundary conditions is a good compromise between prediction accuracy and availability of parameters from conventional triaxial compression testing. The results of this investigation give confidence that numerical FLAC models using this simple soil constitutive model are adequate to predict the performance of reinforced soil walls under typical operational conditions provided that the soil reinforcement, interfaces, boundaries, construction sequence, and soil compaction are modeled correctly. Further improvement of predictions using more sophisticated soil models is not guaranteed. [ABSTRACT FROM AUTHOR]

The paper describes a series of short-term in-isolation tensile tests that were carried out to investigate the load–strain–time performance of typical knitted polyester (PET), biaxial polypropylene (PP) and uniaxial high-density polyethylene (HDPE) geogrid products. The specimens were subjected to constant rate of strain (CRS) loading and variable rate of strain (VRS) loading. Variables between test specimens included specimen length and specimen aspect ratio (e.g. number of ribs). A novel feature of these tests was that internal strains in the specimens were recorded using non-contact measurements taken with a video-extensometer apparatus. The data shows that at large strains the PP and HDPE geogrid specimens exhibited large lateral strains while lateral strains were negligible for the PET product. Results of CRS tests carried out with different specimen aspect ratios showed that there was no change in tensile strength, axial strain and lateral strain at rupture for HDPE and PET materials. The PP material in this investigation did show an increase in axial and lateral strain at rupture for a specimen tested at an aspect ratio approaching one. The polyolefin geogrids (PP and HDPE) were shown to exhibit tensile stiffness and ultimate tensile load capacities that increased with rate of strain. Implications of the contractive behaviour of the polyolefin geogrid products to the selection of in-soil reinforcement stiffness values and rheological modelling are identified. [Copyright &y& Elsevier]

The paper describes limit equilibrium analyses of two large-scale geosynthetic reinforced soil embankments and one unreinforced soil embankment that were taken to collapse under a strip footing placed close to the crest. One reinforced embankment was constructed with a relatively extensible and weak polypropylene geogrid and the second with a relatively strong and stiff high-density polyethylene geogrid. The geometry of the embankments and the loading arrangement were the same for all three structures. The focus of the paper is on a comparison of the predicted collapse load for the three structures and the actual observed values. A three-dimensional analytical approach is used to account for possible side-wall friction effects due to the test facility in which the large-scale experimental models were built. The paper also reports details on the interpretation of in-isolation constant load tests and strain measurements used to infer tensile loads in the reinforcement at failure. An important conclusion is that a general two-part wedge analysis approach can be used to predict the collapse footing load for both unreinforced and reinforced sand embankments in this investigation provided careful attention is paid to the selection of soil shear strength and reinforcement tensile capacity. [ABSTRACT FROM AUTHOR]

The paper describes an experimental investigation in which two large-scale geosynthetic reinforced soil embankments and one unreinforced soil embankment were taken to collapse under a strip footing placed close to the crest. One reinforced embankment was constructed with a relatively extensible and weak polypropylene geogrid and the second with a relatively strong and stiff high-density polyethylene geogrid. The geometry of the unfaced embankments, sand soil, and loading arrangement were the same for all three structures. The focus of the paper is on the experimental design, construction, testing, and instrumentation techniques used in the investigation and selected test results. The results of the study show that the ultimate footing load capacity increased with an increase in reinforcement strength (and stiffness) and that the reinforced soil embankments had a load capacity up to 1.6–2.0 times that of the nominal identical control embankment without reinforcement. [ABSTRACT FROM AUTHOR]

Abstract: The paper describes the novel use of recycled construction and demolition waste (RCDW) material as the backfill material in an otherwise conventional 3.6-m high wrapped-face geosynthetic reinforced soil wall. The wall was constructed over a collapsible foundation soil which is common in the area around the capital city of Brasilia. The wall was instrumented and then monitored though dry and wet rainy seasons. The influence of cumulative rainfall on foundation compressibility was detectable and seasonal wetting and drying was shown to quantitatively influence wall deformations, settlement, horizontal earth pressures and reinforcement strains. Nevertheless, wall performance was judged to be satisfactory when compared to the performance of other walls of similar size constructed with traditional select granular soils over non-collapsible foundation soils. The results of this investigation demonstrate that significant project cost savings may be possible by avoiding more expensive traditional backfill materials and larger societal economic savings accrued by diverting RCDW waste streams from landfills. [Copyright &y& Elsevier]