FPInnovations, in cooperation with the Canadian Forest Service, Alberta Transportation, Laval University i3C Chair, and the City of Edmonton recently completed a review of Alberta’s starting threshold for initiating winter weight hauling. The threshold was 1 m frost depth but neither Alberta, nor any other jurisdiction, had undertaken a formal engineering analysis of the structural capacity of freezing pavements. The objective of this project was to determine the minimum frost depth at which hauling at winter weight premiums in Alberta could start without compromising pavement service life.
The paper describes the process used to develop a robust, validated, model capable of estimating the structural capacity of freezing highway pavements. This included analysis of freezing patterns in Alberta, resilient modulus testing of frozen roadbed materials, full scale accelerated trafficking test of two freezing pavements, and model development and validation. Based on this work, in December 2017, Alberta Transportation reduced the starting frost depth threshold used in its winter weight policy from 1 m to 0.75 m.
Substantial benefits to the public, forest industry, and the heavy haul industry are expected from a longer winter weight period and (or) a shallower frost depth threshold. The forest industry is predicted to realize $1.63M in haul savings for each additional week of hauling with winter weights. Given a shallower frost depth requirement, more participation in the winter weight program in the south of the Province and during warmer winters will be possible. The Province is predicted to see savings in pavement rehabilitation costs of between $1M and $2.5M per year arising from some truck volume moving from summer to winter.