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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 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]