MECHANISTIC DESIGN: A MODELING CASE STUDY FOR THE CITY OF SASKATOON

摘要

A mechanistic roadway design methodology was employed for City of Saskatoon roadways as part of a pilot study. The mechanistic design methodology included Saskatoon field state conditions of subgrade materials, changing moisture contents, and alternative road building materials. This design methodology used is comprehensive and based on regulated standards, mechanistic materials testing, and modeling. A finite element method was used to conduct a mechanistic primary response analysis to determine road design pavement structure options. This paper describes a road design case study for City of Saskatoon new subdivisions. Laboratory testing was conducted to assess the soil and aggregate material properties of sampled subgrade. Both conventional and mechanistic materials libraries were developed for subgrade and other pavement structure materials. The conventional materials library included material properties such as gradation, plasticity, and density and the mechanistic library included material properties such as dynamic modulus and Poisson's ratio. The model used these material properties as inputs and the finite element method to perform simulations and generate model outputs. For this project, the outputs were different pavement structure design options based on maximum peak surface deflections allowed. The critical vehicle loads for City of Saskatoon collector and local roads is a vehicle loaded to primary weight limits. For this new subdivision design case study, standard conventional pavement structures currently used for local roads and collector roads were modeled as a baseline and compared to alternative road structures with additional base material, a sand drainage layer, and a rock drainage layer for one subgrade type. For each resultant cross section generated by the model, the shear strains were analyzed and maximum peak surface deflections were used to assess which cross section was optimum for each subgrade type. The results of this case study showed that the mechanistic model provided feasible alternative pavement structures for City of Saskatoon local and collector roadway design. This study illustrated that using the standard pavement structures for local roads currently used by the City's design methodology may not be structurally appropriate for roads in new subdivisions with varying subgrade types.