RATIONAL METHOD FOR SEASONAL LOAD LIMITS FOR FLEXIBLE PAVEMENTS

Special temporary restrictions on allowable axle weights (load limits) may be applied to older or light pavement sections in seasonal frost areas. Load limits are used to prevent accelerated deterioration and premature failure of spring-thaw weakened pavements. In current practice the magnitude, duration, and date of initiation of seasonal load limits are selected on the basis of the pavement's previous performance and the judgement of the responsible highway manager. This paper describes a new approach to load limit selection based on controlling seasonal rates of fatigue life consumption. Rates of fatigue life consumption for flexible pavements can be determined using fatigue curves in conjunction with Miner's hypothesis of linear summation of cycle ratios. Fatigue curves relate critical tensile strains in the pavement section to the number of load repetitions causing fatigue failure. Strains in the pavement section are computed from layered-elastic theory. Using available computer programs, the pavement response is determined for the traffic loads applied to the pavement while it is in its various seasonal physical states. Seasonal values of pavement and subgrade elastic response parameters (resilient modulus and Poisson's ratio) are determined in laboratroy repeated load tests conducted on appropriately prepared and conditioned specimens. By relating the cumulative damage produced to the number and magnitude of loads applied during each of the seasonal pavement conditions, the effects on remaining pavement life of alternative load limit enforcement policies can be compared. In a trial application of the method to an Idaho pavement constructed on a decomposed granite fill suggrade, it was decided that the maximum axle load to be permitted during the spring-thaw period should be stricted to one which produced the same rate of fatigue consumption as the normal (summer-fall) legal maximum axle load (18.9 kips). Using this criterion, the maximum spring-thaw period axle load for the pavement was 11.5 kips. The Idaho Transportation Department's posted limit for the pavement was 14.0 kips. A relative fatigue comparison indicated that the remaining service life under the 14.0 kip spring-thaw load limit is 80 percent of the life remaining if the 11.5 kip limit is imposed. It was determined that if no special spring-thaw period load limit is imposed (or enforced), the remaining service life of the pavement will be reduced to 40 percent of the life remaining under the 11.5 kip limitation. (Author)

  • Supplemental Notes:
    • Proceedings of the Eighteenth Annual Engineering Geology and Soils Engineering Symposium, held at the Red Lion Inn, Boise, Idaho.
  • Corporate Authors:

    Idaho Transportation Department

    3311 W State Street, P. O. Box 7129
    Boise, ID  United States  83707-1129

    University of Idaho, Moscow

    Department of Geology and Geological Engineering
    Moscow, ID  United States  83844-3025

    Boise State University

    Department of Geology and Geophysics
    Boise, ID  United States 

    Idaho State University, Pocatello

    Department of Geology
    Pocatello, ID  United States  83201

    Idaho State University, Pocatello

    Department of Geology
    Pocatello, ID  United States  83201
  • Authors:
    • Hardcastle, J H
    • Lottman, R P
    • Buu, T
  • Conference:
  • Publication Date: 1980-4

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 301-322

Subject/Index Terms

Filing Info

  • Accession Number: 00334074
  • Record Type: Publication
  • Files: TRIS, STATEDOT
  • Created Date: Sep 16 1981 12:00AM