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Staged Road Construction in Very Weak Subgrade Using Polymeric Geocell


The ongoing development of the energy industry in Canada, especially for pipeline-related structures, demands innovative ways of access construction. Most of these are at remote locations and under difficult geotechnical conditions making access a challenge. A 4.1km long unpaved access road leading to a proposed compressor station in Blainville, Quebec was planned for the construction of the station pad and future access. The road was expected to serve as a material haul road for the 200m x 250m gravel pad, regular compressor station construction loads, and future traffic. Construction of the pad was scheduled to start before the winter of 2020. The proposed road alignment had very soft to soft subgrade conditions with saturated peat. There were problems with limited right of way, a landslide-prone zone, a creek crossing, and overhead powerlines. The road geometry was to be designed such that there was enough clearance from the overhead powerlines and the slide-prone area and maintain the minimum turning radius required for the long and heavy trucks carrying compressor units. Additionally, there were constraints imposed in permits and other aspects of the project that left a short 6-week window for the construction of the road.
The existing subgrade was high water-bearing peat with depth varying from 0.6m to 2m. Removal of the peat and bringing engineered fill was not practical from cost, schedule, and environmental permit perspectives. A non-conventional design on top of a weak subgrade with geocell was deemed necessary.
The limited construction schedule did not allow for building the minimum reinforced structure necessary to support design loads, particularly the 65 Metric Ton compressor load. As an engineered solution, a road was initially designed for the design load limits and a maintenance plan for the operation. Taking advantage of the high-strength novel polymeric alloy (NPA) geocell load support mechanism, it was possible to avoid any material removal and yet build a minimum structure for initial construction traffic including some heavy haul traffic. Strict load restrictions were imposed on the temporary bridge. The initial design was done in a way to accommodate the final construction with minimum adjustments and without hindering continuous access to the pad. For low power lines and right of way, fill limits on the final design were further reduced with an additional layer of geocell. This paper describes in detail the design methodology and maintenance program that was implemented through the construction phases.

Conference Paper Details

Session title:
Pavements - Innovations in Pavement Management, Engineering and Technologies
Chatterjee, Arghya K.
Pokharel, Sanat K.
Breault, Marc