Reinforcement and separation for gravel access road
Building and maintaining unpaved access roads through the forests and grasslands of the Kamloops area of British Columbia can present contractors with considerable challenges for soil stabilisation. Weak or variable soil conditions, combined with relatively high rainfall levels, mean that many roads and tracks suffer problems with rutting and intermixing of the cover material into the subsoil. When Argo Road Maintenance Inc., working for The British Columbia Ministry of Transportation, was recently contracted to upgrade a single lane gravel road in Monte Creek, they were faced with an existing road which had extensive deep rutting throughout.
Ongoing maintenance costs for the road were spiraling and, with road gravel mixing with the soil and disappearing with traffic, Argo knew that simply adding more aggregate would only provide a short-term fix. A permanent solution was required that would provide both reinforcement and separation. Argo Road Maintenance, along with the Ministry of Transportation, first considered using separate rolls of geotextiles and bi-axial grids. However, because installation would have been complicated by using multiple rolls of two products with excessive overlaps, a single-roll, multifunctional product solution was sought. It was decided to appoint NAUE Geosynthetics’ Canadian distributor, Brock White, to carry out trials using NAUE’s Combigrid® geogrids. Selected for the trials was Combigrid® 30/30 Q1 151 GRK 4 C – a single product geocomposite, developed specifically for ground stabilisation, which combines a 30kN polypropylene geogrid and a 150g/m² geotextile. Combigrid® is a composite product of a Secugrid® geogrid, with a needle-punched Secutex® nonwoven geotextile firmly welded between the reinforcement bars. This technology has proven to be ideal for construction on soft soils, providing immediate reinforcement, separation, filtration and drainage, all in one product. Combigrid® geogrids have a high resistance to installation loads and can effectively prevent the migration of fine particles into the base course. Combigrid® 30/30 Q1 151 GRK 4 C was approved for the project and a total of twenty 100m long rolls were supplied. Prior to installation of the Combigrid®, the full length of the existing road bed was graded to a level and, as the 4.75m wide rolls matched the road width, this meant that Argo Road Maintenance was able to rapidly lay the Combigrid® by simply rolling out the material without the need to employ specialist techniques or equipment. 150mm of aggregate cover was then spread and compacted to complete a Combigrid® reinforced access road, with significantly increased bearing capacity. Furthermore, because the road was a single lane construction with no place for trucks to turn around, the durability of Combigrid® was put to the test by having to withstand the constant toing and froing of heavy vehicles over its surface. It was the first time that NAUE products had been employed by Argo Road Maintenance and the British Columbia Ministry of Transportation. Brock White reports that both parties were impressed with how Combigrid® performed in extremely soft soil conditions.