Evaluation of an Operator’s Horizontal Directional Drilling Pipeline Installation Inventory and Recommended Practices

Abstract Horizontal directional drilling (HDD) is a common pipeline installation method increasingly preferred to avoid challenging terrain, geohazards, and environmentally sensitive areas that would otherwise be encountered with conventionally trenched installations. However, HDD pipeline installations (HDDPIs) are not always designed to avoid geohazard threats, with pipelines often drilled through areas vulnerable to watercourse floodplain erosion or landslides. This can increase pipeline susceptibility to failure up to 15 times compared to conventionally trenched pipelines [1]. Failure to adequately design for, monitor, assess and manage geohazard threats to HDDPIs has resulted in failures, environmental impacts, lengthy pipeline outages and costly HDDPI replacements. This paper presents an operator’s review of 429 HDDPIs and a proposed standard for classifying, evaluating, monitoring, and mitigating landslide and watercourse threats to both planned and existing HDDPIs. Geotechnical HDDPI hazard sites are classified and assessed by drill path position and ground/pipeline monitoring. Hydrotechnical HDDPI hazard sites are reviewed based on depth of cover, historical air photos, and river geomorphology, and categorized according to likelihood of failure based on potential free span length as related to river size, and estimated time to pipeline exposure. Depending on categorizations, various ground and pipeline monitoring, investigations, and mitigations are prescribed.