Evaluation of Pre-1994 Ontario Highway Edge Drain Practice

Abstract

Presented are results from excavations made to evaluate the performance of various types of edge drains at selected locations on Ontario highways. The pavements are founded on both clay and sand subgrades. The edge drains excavated include Geocomposite Edge Drains, Geotextile Sock-Wrapped Pipe Edge Drains and Geotextile-Wrapped Aggregate Edge Drains. Installation techniques included: Ploughed-in-Place, Trench Excavation, and Mechanical Trencher and Boot. All edge drains were installed after the highway was completed (i.e. retrofit construction). In each case the backfill used was the excavated or displaced shoulder Granular ‘A’ material (typically similar to ASTM D-2940). The observations and resulting test data obtained show differences between the installation concepts and asbuilt construction. Drains that were installed adjacent to and in contact with the pavement edge were found to be separated from the pavement edge by eroded/pumped fine soil particles. This seriously compromised drainage, particularly from any open-graded drainage layer. Tests showed that the granular backfills were up to 1000 times less permeable than the geotextiles used for the edge drains. Recommendations are made for the installation of retrofitted edge drains.