Abstract
Horizontal directional drilling (HDD) is a method of trenchless pipeline installation which has been widely used in the Western Canadian Sedimentary Basin (WCSB) during the past 40 years to cross challenging terrain, including watercourses and slopes. In the case study presented, 7,952 pipeline slope crossings are considered, of which an estimated 14% are partially or fully crossed by HDD. Often the primary objective of the HDD installation at the time of construction was to cross a watercourse and adequate consideration was not always given to the possible presence of landslide terrain adjacent to the watercourse. Minimizing HDD cost often requires shallower and shorter installations, which combined with the practice of not always identifying existing landslide features resulted in an estimated 16% of HDD landslide crossings spatially intersecting landslides. Due to the increased stiffness and overburden stress of soil or bedrock with depth as well as other factors, pipeline vulnerability and hence probability of failure is significantly increased relative to shallower conventionally trenched pipelines. Within the case study inventory, the combination of historical HDD installations that did not effectively avoid landslides and the increased vulnerability of pipelines impacted by landslides at depth accounted for approximately 35% of landslide related pipeline failures within a recent 10-year period, a failure rate approximately 15 times that of conventionally trenched pipelines when adjusted for frequency of landslide intersection.
Many pipeline operators have recognized the disproportionate risk landslides pose to ineffective HDD installations and are prioritizing assessment and management accordingly. This paper proposes a screening framework to provide guidelines for evaluating the effectiveness of HDD installations avoiding landslides for both existing and planned installations.
