Modeling the Structural Response of Urban Subsurface Drainage Systems

In recent years, many City of Saskatoon (COS), Canada, roads have experienced premature failures. High water tables, increased precipitation, and poor surface drainage have caused increased moisture infiltration in road structures. Further deterioration of these aged pavements is attributable to heavy year-round loadings in urban traffic. To address these issues, COS piloted subsurface drainage and strain dissipation layers in some roads. These drainage systems were constructed with crushed portland cement concrete (PCC) rock and conventional virgin crushed rock. Given the empirical nature of conventional road design methods currently used by COS, the structural benefits of drainage systems are difficult to quantify. Therefore, a reliable method that directly incorporates recycled materials, substructure drainage systems, and diverse field conditions is needed. A mechanistic analysis of the drainage systems was piloted in rehabilitated COS pavement structures with a three-dimensional (3-D) nonlinear orthotropic computational road structural model. The 3-D mechanistic model was used to predict peak surface deflections and normal and shear strains in the structure. Modeling results showed that constructing pavement structures with a substructure drainage layer of crushed PCC rock improved the structural performance of the road system in terms of strains under applied traffic loads. The road model provided primary response predictions that correlated with deflections measured by a heavy weight deflectometer, before and after construction. Therefore, the road model used is a reliable pavement engineering analysis tool able to predict the in-field structural behavior of various road structures under diverse field state conditions.