Prince George LPR Corrosion Monitoring
Project Gallery
ERTesting, at McMahon & Mann Consulting Engineers, P.C., was engaged to design and install a corrosion monitoring system for a hollow-bar soil nail retaining wall in Prince George, British Columbia. The soil nail wall supports a side hill cut serving as a grade separation between the north and southbound lanes of Highway 97. The wall is approximately 2000 feet long and is more than 40 feet high at its tallest point. Due to challenges associated with incorporating corrosion protection measures, hollow-bar soil nails are designed with sacrificial steel. Proper selection of sacrificial steel requires knowledge of corrosivity of the subsurface environment and an estimate of metal loss expected to occur over the 100-year design life of the facility. The British Columbia Ministry of Transportation and Infrastructure (Owner) included installation of a corrosion monitoring system in its construction contract with Windley Contracting, Ltd (Windley) to document corrosion rates and check if the wall will meet the intended service life given the sacrificial steel that is incorporated into the design.
Windley engaged ERTesting to install 10 corrosion monitoring stations across the soil nail wall and collect initial measurements. ERTesting configured the system to facilitate corrosion rate measurements via the linear polarization resistance technique. ERTesting completed the installation and obtained initial measurements from these stations during June 2018 shortly after construction of the soil nail wall was completed. These measurements showed that corrosion rates were close to the values assumed in design for selection of sacrificial steel. The effects of variations in moisture contents of the native soil and the effectiveness of the grout cover surrounding the soil nails to mitigate corrosion were also evident on these data. Data showed that the grout cover did not always serve to mitigate corrosion, although the effect of the grout cover was not considered in the design and selection sacrificial steel.
