INTERPRETING DYNAMIC SURFACE DEFLECTIONS IN THE GRANULAR BASE LAYER OF THE PAVEMENT STRUCTURE

This report presents the results of a follow-up study to further investigate the initial findings of an earlier University of Maryland research project. The principal objective was to explore the consistent lack of agreement between field measured deflections and those computed using elastic-layered theory. During several periods of the year, surface deflections were measured with the FHWA Thumper testing vehicle on three Maryland flexible pavement sections. Using an iterative stress-dependent modification for both unbound granular material and fine-grained cohesive subgrades, these field deflections were mathematically predicted for a large number of specific test conditions. Although these predicted deflections failed to match the measured values, a consistent trend in the ratio of the corresponding deflections was detected. As suggested in a previous study, an adjustment factor, K1, was applied to the granular base modulus to cause the deflection ratio to approach one. Linear log-log relationships were derived between decreasing K1 and increasing measured deflection values. From this analysis, it was surmised that current laboratory methods of granular material characterization appear to be inadequate for modeling in-situ behavior. Further analysis was made to examine the shear strain in the granular layer. A clear curvilinear plot was produced, indicating the adjustment to the granular modulus is related to the shear strain which develops in response to the surface loading. As a result, a procedure was presented for correcting for the effective in-situ granular base modulus and estimating the subgrade modulus with deflection measurements. (FHWA)

• Corporate Authors:

  Federal Highway Administration

  Office of Research, 1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • May, R W
• Publication Date: 1981-2

Media Info

• Pagination: 135 p.

Subject/Index Terms

• TRT Terms: Deflection; Elasticity (Mechanics); Forecasting; Granular bases; Modulus; Pavement layers; Strain (Mechanics); Subgrade (Pavements); Surfaces
• Uncontrolled Terms: Pavement structure
• Old TRIS Terms: Elastic theory; Strains
• Subject Areas: Design; Geotechnology; Highways; Pavements; I22: Design of Pavements, Railways and Guideways; I23: Properties of Road Surfaces;

Filing Info

• Accession Number: 00377225
• Record Type: Publication
• Report/Paper Numbers: FHWA-RD-80-149 Intrm Rpt., FCP 25D1-262
• Files: TRIS, USDOT
• Created Date: Aug 30 1983 12:00AM