Assessment of Subgrade Soils for Pavement Design for Highway 407, East Extension Pickering to Oshawa, Ontario

Although a variety of different input is required for roadway design, subsoil characteristics are one of the key inputs.

In Phase 1 of the extension of Highway 407 eastbound (Pickering-Whitby-Oshawa) and the connection to Highway 401 (West Durham Link), the subgrade soil was observed, described and sampled in nearly 500 exploratory drill holes, evenly spaced along the route, over nearly 30 km. The subgrade soil resilient modulus was measured using a LWD deflectometer in some holes where fairly shallow fill was planned.

The mechanical characteristics of the subgrade soil, mainly ranging from silty sand to sandy silt in the northern section and from silty clay to clayey silt in the southern section, were determined using CBR and resilient modulus testing in the laboratory.

The thermal characteristics of the subgrade soil were determined using soil segregation potential tests (SP0) and standard geotechnical tests (granulometric analysis, sedimentation analysis, Atterberg limits and methylene blue detection limits).

Various correlations were established between the different results obtained to achieve the most accurate possible characterization of the materials while avoiding long and costly testing. The methodological approach used to adequately characterize these subgrade soils will be presented.