Evaluation and suggested improvements to highway edge drains incorporating geotextiles: Fid-Bau Portal

Evaluation and suggested improvements to highway edge drains incorporating geotextiles

Raymond, G.P. / Bathurst, R.J. / Hajek, J.

Design recommendations for retrofitted highway edge drains are presented. The recommendations are based on results from excavations made to evaluate the performance of various types of geosynthetic edge drains at selected locations on Ontario's highways. The evaluations include observations from excavations at highways built on both clay and sand subgrades. The geosynthetics excavated include geocomposite edge drains, geotextile-wrapped pipe edge drains and geotextile-wrapped aggregate edge drains. The edge drains were installed using various techniques that included: ploughed-in-place, trench excavation, and mechanical trencher and boot. The excavated edge drains were installed either as part of pavement construction or retrofitted several years after the original construction. All excavated edge drains used the pre-installed (existing) excavated or displaced shoulder Granular 'A' as backfill to the installed drain. Two main observations are: (a) drains that were installed adjacent to and in contact with the pavement edge (in North American terminology the pavement surface refers to the driving surface) soon became separated from the pavement edge by eroded/pumped fine soil particles seriously compromising the performance of the pavement subdrain systems, particularly where an open-graded drainage layer (OGDL) was used; (b) the granular backfill was considerably (up to 1000 times) less permeable than the geotextiles used for the edge drains. These and other problems form the background for the recommendations for the design and installation of retrofitted edge drains to ensure satisfactory field performance.