Development of a Methodology for Posting Load Limits on Load-Zoned Pavements: Interim Report (1701-1)

Load-zoned pavements in Texas are presently posted using gross vehicle weight (GVW) limits to prevent or minimize the development of permanent deformation due to excessive truck loads. In reality, pavement damage is more related to axle loads and axle configuration rather than GVW. Thus, load restrictions need to be related to axle loads, axle type, pavement structure, and material characteristics. To address this need, the Texas Department of Transportation (TxDOT) initiated a study with the Texas Transportation Institute (TTI) to develop a procedure for posting or removing load limits based on predicted pavement performance. For this purpose, non-linear elastic and nonlinear elasto-plastic programs were developed to predict the structural adequacy of pavements using the Mohr-Coulomb failure criterion. The stress-dependent behavior of pavement materials is considered based on the Universal Soil Model.This research report presents the results of the work conducted during the first year of the study. Initially, researchers undertook a review of the current practice in Texas to identify the needs that should be addressed in this development work. In addition, a review of load-zoning practices in other agencies was conducted. Findings from the literature survey are summarized herein. Using the programs developed and existing performance models, researchers conducted a sensitivity analysis to identify the factors that significantly influence predicted pavement response and performance. By evaluating the changes in the predicted plastic strains, yield function, and service life with changes in the factors considered, their influence on predicted pavement response and performance was established.To evaluate the permanent deformation behavior of pavement materials under repeated loadings, researchers also conducted repeated load-permanent deformation tests on a number of base and subgrade materials at various moisture contents and stress conditions. Observations from the laboratory tests were reviewed in relation to known physical behavior and engineering experience. The data from the permanent deformation tests will be used in developing a model to predict rutting in flexible pavements for evaluating load restrictions. This development work is still on-going.