DANISH EXPERIMENTS WITH THE FRENCH FALLING WEIGHT DEFLECTOMETER

The falling weight deflectometer is a portable apparatus used for measuring the deflection of a road surface under the influence of a load pulse of very short time duration. This pulse simulates a fast moving wheel load, and it can be adjusted to correspond to any desired wheel load of 5 tons (5000 kp.) or less. The unit is built into a trailer frame, which is easily pulled by a passenger automobile. To date, about 20 falling weight deflectometers have been produced in Denmark. The validity of comparing the effect of the falling weight to the effect of a moving wheel load has been investigated by two means, both of which showed good correlation between the two effects. One set of measurements was undertaken in Holland, where photo-electric equipment was used to measure the deflection due to a passing wheel load. Another set of measurements was undertaken in Denmark, using an accelerometer. The acceleration signal was integrated twice with an analog integrator to obtain the deflection in question. Static and dynamic surface deflection tests have shown poor correlation to each other, especially for roads with thick asphalt concrete layers. Investigations undertaken on a Danish experimental road, on the other hand, showed good correlation between dynamic deflection measurements and the corresponding theoretical elastic deflection values. The asphalt concrete moduli used in these theoretical calculations were the results of dynamic three-point bending tests. The moduli of the unbound layers were found by low frequency sound wave measurements taken on-site. Curves are shown which allow conversion of measured deflections from an arbitrary temperature between 5 C and 30 C to the corresponding deflections at 20 C (standard temperature). The 20 C curve can then be used to analyse certain limiting criteria. The limiting criteria are the strain in the bottom of the asphalt concrete layer and the verticle stress on the subgrade. These can be set to whatever values are deemed reasonable at the 20 C standard temperature. Finally, the diagrams can be used to help find the necessary thickness of a possible additional asphalt concrete reinforcement layer. /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:
    • Bohn, A
    • Ullidtz, P
    • Stubstad, R
    • Sorensen, A
  • Conference:
  • Publication Date: 1972-9

Media Info

  • Features: Appendices; Figures;
  • Pagination: p. 1119-28
  • Serial:
    • Volume: 1

Subject/Index Terms

Filing Info

  • Accession Number: 00261888
  • Record Type: Publication
  • Report/Paper Numbers: Proceeding
  • Files: TRIS
  • Created Date: Oct 22 1974 12:00AM