ASPHALT PAVEMENT DESIGN--THE SHELL METHOD

The method is based on a model in which the pavement structure is regarded as a linear elastic multi-layered system in which the materials are characterised by their modulus of elasticity and Poisson's ratio. The computer program BISAR is used to compute all stresses, strains and displacements at any point in the system under any number of vertical and/or horizontal surface loads. In this way, the primary design criteria have been established, i.e. the compressive strain at the top of the subgrade and the horizontal tensile strain in the asphalt. Secondary criteria such as permissible stresses in cementitious base layers, permanent deformation of the asphalt, etc., are also included. The permissible value for compressive subgrade strain has been derived from analysis of AASHO Road Test sections and structures conforming to CBR design. The permissible asphalt strain was determined from extensive laboratory measurements for various mix types at different stiffness moduli of the asphalt. In the application of the asphalt fatigue criterion allowance is made for the influence of the transverse distribution of wheel loads and for effects of healing and intermittent loading. The traffic data are converted into an equivalent number of standard design axle load applications. To introduce the influence of the ambient temperature a procedure has been developed to relate the mean annual or monthly air temperature to an effective asphalt temperature, depending on the thickness of the asphalt. The moduli of subgrade and unbound base layers should be determined at appropriate stress levels whereby the latter modulus is a function of the subgrade modulus. It is demonstrated that the modulus of a given mix, relevant for the structural design, can also be derived with sufficient accuracy using a nomograph to provide a practical system for road engineers, sets of design charts have been prepared from which combinations of thicknesses of the asphalt and unbound base layers can be derived for various mean annual temperatures, for a number of typical mixes and for various sugbrade moduli. Special attention is paid to a method of predicting the permanent deformation (rut depth) of the asphalt layers during the expected service life of the pavement. The application of the design method to the design of pavements for aircraft with multiple wheels is also dealt with the various laboratory tests and full scale road trials carried out to investigate the validity of the design method have been summarised. The practical use of the design method is illustrated by means of some examples. /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
  • Edwards, J M
  • Sommer, P
  • Uge, P
• 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: Appendices; Figures; References; Tables;
• Pagination: p. 39-74

Subject/Index Terms

• TRT Terms: Computer programs; Deflection; Deformation; Flexible pavements; Forecasting; Loads; Mathematical models; Modulus of elasticity; Pavement design; Poisson ratio; Strain (Mechanics); Stresses; Subgrade (Pavements); Temperature; Wheel loads
• Uncontrolled Terms: Loading; Models
• Old TRIS Terms: Poissons ratio; Strains
• Subject Areas: Highways; Pavements;

Filing Info

• Accession Number: 00170207
• Record Type: Publication
• Report/Paper Numbers: Proceeding
• Files: TRIS
• Created Date: Mar 14 1978 12:00AM