Pipeline integrity has been threatened at the Dead Horse Creek pipeline crossing in southern Manitoba by a slow-moving slope failure with a potential for crest retrogression. The movement zone extends from the slope crest to the bottom of the creek, a vertical distance of about 25 m and is approximately 80 m long from toe to scarp and 100 m wide along the creek. The slope has degraded over time and is controlled by the combination of local geology, which consists of weak colluvium overlying high plastic clay shale, and creek bank erosion and channel degradation. Saturated soil conditions, a function of poor drainage and elevated seasonal precipitation, have exacerbated the problem over the years.
The slope movements have been monitored on a regular basis since 2008 and presented an increasing risk to the integrity of multiple pipelines located in two rights-of-way (ROWs) situated within and immediately adjacent to the failing soil mass. The site is surrounded by various infrastructure and recreational areas that are key to the community, and therefore is considered a high consequence area with respect to potential pipeline failures. To manage the risk and protect pipeline integrity, various stress relief and other mitigating measures have been implemented since 2013 , culminating in a major slope rehabilitation project undertaken in 2015, which comprised earthworks, drainage and watercourse improvements, and slope stabilization using stone columns.
While the use of stone columns to stabilize embankments is not a new technique, it is not commonly used in the pipeline industry and represents another option for geohazard stabilization in the right situations. This paper presents the slope stabilization techniques employed and discusses the challenges of working on an active moving slope confined by a watercourse and live pipeline assets. The positive benefits of the stabilization measures are illustrated through the use of 2D and 3D numerical modelling, and confirmed through an ongoing geohazard management program that includes site inspection and instrumentation monitoring which continues to show improvements in slope performance post construction.