PAVEMENT EVALUATION AND OVERLAY DESIGN--THE SHELL METHOD

A method is presented for evaluating pavements by driving the structural properties from the shape of the reflection bowl under a test load. The structural properties of the existing pavement are expressed in terms of effective layer thicknesses and Young's moduli of the materials. The shape of the deflection bowl is characterised by the ratio of the deflection at a given distance from the load to that measured under the centre of the test load. Charts prepared from computations with the BISAR computer program for multi-layer elastic systems are used for the interpretation of the deflection measurements. The method can be used, in principle, in conjunction with any type of test load, provided that the appropriate loading conditions are taken into account. Preferably, the measurements are conducted with the Falling Weight Deflectometer (FSD) since its characteristics of force level and loading time are more representative of heavy traffic than most other systems, which are affected adversely by the configuration of the loading and recording system and/or by indirect measurement of deflections. Preliminary studies demonstrated that satisfactory results were obtained with a prototype FWD. The data in this paper were obtained with a new FWD modified to allow quick operation with remote control for routine pavement evaluation. Special attention is given to routine operation, including data processing, and to the interpretation of the measurements on more complicated structures such as those with cementitious base layers. From the structural properties of the pavement, derived from the deflection bowl measurements and the number of axle loadings carried during service, the residual life of the pavement, expressed in terms of the number of standard axle load applications, can be determined. This information is used to estimate the overlay thickness required for future estimated traffic, using the newly developed design method, in which influences of climate and a asphalt mix type can be taken into account. Practical examples of the evaluation and overlay design method are given. /Author/

• Supplemental Notes:
  • Volume I of proceedings of 4th International Conference on Structural Design of Asphalt Pavements, Ann Arbor, Michigan, August 22-26, 1977.
• Corporate Authors:

  University of Michigan, Ann Arbor

  Department of Civil Engineering
  Ann Arbor, MI  United States  48109
• Authors:
  • Claessen, AIM
  • Ditmarsch, R
• Conference:
  • Volume I of proceedings of 4th International Conference on Structural Design of Asphalt Pavements, Ann Arbor, Michigan, August 22-26, 1977.
• Publication Date: 1977-1

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 649-662

Subject/Index Terms

• TRT Terms: Axle load force; Computer programs; Deflection; Deflectometers; Evaluation; Forecasting; Loads; Modulus of elasticity; Overlays (Pavements); Pavement design; Pavement layers; Pavement performance; Pavements; Testing; Thickness
• Uncontrolled Terms: Pavement thickness
• Old TRIS Terms: Pavement deflection
• Subject Areas: Highways; Pavements;

Filing Info

• Accession Number: 00170241
• Record Type: Publication
• Report/Paper Numbers: Proceeding
• Files: TRIS
• Created Date: Mar 29 1978 12:00AM