Date of Award

5-2001

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

William G. Davids

Second Committee Member

Eric N. Landis

Third Committee Member

Vincent Caccese

Abstract

Flexible pavements or roads surfaced with asphalt have been in use for the past 100 years. Currently, the design of flexible pavements is largely based on empirical methods. However, there is currently a shift underway towards more mechanistic design techniques. While layered elastic analysis and two-dimensional finite element (FE) methods have been generally been used to determine stresses, strains and displacements in flexible pavements, they suffer several severe limitations. To overcome these difficulties, three-dimensional (3D) FE analysis must be used to analyze pavement structures. This study focuses on exploring the use of 3D finite-element methods to examine the response of flexible pavements.

For this study, an efficient 3D FE meshing tool was developed. This meshing tool allows us to develop models of layered system, inter-layer debonding and slip, various wheel and axle loadings. The 3D FE models were tested by comparing predicted results with experimentally measured field data. Critical finite-element model dimensions were determined, and material properties were back-calculated to give good comparisons with field-measured data.

Since the stress-strain response of granular materials is non-linear, the use of the stress-dependent K-8 model was investigated. Two implementation methods were considered. It was shown that the analysis results are very different depending on the method of implementation.

When applying wheel loads, it is quite typical that a constant tire/pavement pressure distribution is assumed over a rectangular or circular area. However, prior investigations have shown that spatially varying tire/pavement contact pressures can affect the response of pavements significantly. In this study, a model was developed to simulate spatially varying tire contact pressures based on previous published data. Paranletric studies were performed to examine the effect of spatially varying tire pressures on pavement response. There studies showed that using spatially varying tire/pavement pressures yields stresses at the bottom of asphalt that are up to 30% larger than those predicted when uniform tire/pavement pressures are assumed. The largest differential occurs in thin flexible pavement structures with a sub-base having a low stiffness. Further, the studies show that for thick pavement sections, predicted tensile stresses in the top of the asphalt are much larger when spatially varying tire/pavement contact pressures are considered.

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