PREDICTION AND OBSERVATION OF THE PERFORMANCE OF A FLEXIBLE PAVEMENT ON THE EXPANSIVE CLAY SUBGRADE.

For an experimental section of road pavement in the Darling Downs, Queensland, investigations carried out earlier on a highly expansive clay subgrade suggested an ultimate equilibrium subgrade suction of the order of 350 p.s.i. or 6 per cent dry of optimum moisture content (OMC) for standard AASHO compaction. During and after construction, rapid drying in the vicinity of the edges of the sealed pavement caused serious longitudinal shrinkage cracking at the edge of the seal in less than 12 months. Subsequent seasonal rainfall entering these cracks led to serious deformations and loss in surface shape and, in many cases, to shear failure. Practical methods are suggested which may overcome these problems. A laboratory programme was devised to investigate the volume change characteristics and repeated loading 'resilient' moduli as functions of subgrade suction and initial compaction. The results indicate that for an expansive clay subgrade, the volumetric and vertical strain can be linearly correlated with the logarithm of the suction over the suction range considered. The compacted material is also isotropic with the vertical strain being exactly one third of the volumtric strain. The repeated loading 'resilient' moduli are very sensitive to suction and the logarithm of the moduli can also be linearly correlated with the suction logarithm. From the 'Shell Rational Method' design charts for lightly trafficked roads, these correlations are found to have a variation of pavement thicknesses from 15 in. at the equilibrium suction to over 4 in. at OMC depending on compaction conditions. Finite element analyses have been made for deformations due to volume changes under changing subgrade moisture conditions and the deformations due to an 18,000 lb axle loading with moisture and stress dependent material properties. These theoretical predictions have been compared with preliminary field observations obtained from the experimental sections. Both the predicted and observed behavior are in general agreement and clearly indicate the important influence of subgrade moisture on the performance of a pavement built on expansive clay subgrades in a semi-arid environment./AUTHOR/

  • Supplemental Notes:
    • Presented at the Third International Conference on the Structural Design of Asphalt Pavements, Grosvenor House, Park Lane, London, England, Sept. 11-15, 1972.
  • Corporate Authors:

    International Conf Struct Design Asph Pvmts (3rd)

    University of Michigan, Department of Civil Engineering
    Ann Arbor, MI  United States  48104

    International Conf Struct Design Asph Pvmts (3rd)

    University of Michigan, Department of Divil Engineering
    Ann Arbor, MI  United States  48104

    Interrational Conf Struct Design Asph Pvmts (3rd)

    University of Michigan, Department of Civil Engineering
    Ann Arbor, MI  United States  48104
  • Authors:
    • Richards, B G
    • Gordon, R
  • Conference:
  • Publication Date: 1972-9

Media Info

  • Features: Figures; References;
  • Pagination: p. 133-143
  • Serial:
    • Volume: 1

Subject/Index Terms

Filing Info

  • Accession Number: 00261965
  • Record Type: Publication
  • Report/Paper Numbers: Proceeding
  • Files: TRIS
  • Created Date: Oct 22 1974 12:00AM