Case Study: Remediation of a Riverbank Slope Failure in the Canadian Prairies

ABSTRACT: A major pipeline crossing of the Souris River in southern Manitoba was undergoing a retrogressive slope failure within the limits of the pipeline corridor. A geotechnical investigation was carried out to assess the subsurface conditions in the slope and mechanism of the slope failure to develop a suitable remediation strategy. Activities included topographical and bathymetric surveys, pipeline surveys, borehole drilling using auger and bedrock coring techniques, and installation of instrumentation such as vibrating wire piezometers and slope inclinometers. The selection of the borehole locations was a challenge due to the many on site constrains such as poor access for the drill rigs, safety concerns on the failed slope, and the presence of five active pipelines within the corridor. To gain critical subsurface information on the failed slope and within the river channel, geophysical surveys were also carried out such as seismic refraction imaging and multi-channel analysis of surface waves. By combining the results of the boreholes and instrumentation with the geophysical survey results, an interpretation of the failure mechanism was completed that allowed the remediation design and construction to proceed. The remediation strategy consisted of addressing a weak toe condition, rebuilding the riverbank using imported fills, providing drainage within the remediated slope, and protecting the final remediated surface with a rip rap armor layer, topsoil and hydroseed, and erosion control blankets on the upper portion of the slope. The observational approach was successfully applied during the construction process so that confirmation of important design elements and changes to the design could be made quickly in the field by geotechnical personnel. Construction of the remediation was completed in the fall of 2016.