Geotechnical Aspects of a Pipeline Rupture in Ecuador: Factors and Mitigation

In February 2009 a pipeline rupture occurred along a sloped section of the Oleoducto de Crudos Pesados (OCP) Ecuador S.A. pipeline. The spill resulted in crude oil flowing down the hillside and into the Rio Santa Rosa. Post rupture investigations were initiated to identify the geotechnical factors that may have contributed to the incident and what mitigation may be necessary to ensure future pipeline integrity. The investigation consisted of several activities including detailed site reconnaissance by a geotechnical engineering team and installation of slope inclinometers to assess ground movements. The intent of the slope inclinometers was to determine the depth, areal extent and rate of ground movement, if any. The post rupture site reconnaissance identified a number of terrain features consistent with shallow ground movement mechanisms. The presence of hummocky terrain could be the result of ground movement or an artifact of the use of the slope as cattle pasture. Five slope inclinometers were installed to assess the slope movements within the project site. Four slope indicators were installed up-slope of the pipeline right-of-way to provide some lateral boundary to the ground movement area. The slope inclinometers showed that in the months following the pipeline rupture the terrain upslope of the pipeline right-of-way was moving at a relative constant rate of about 0.45 mm/day. As a result of the geotechnical investigations an integrity mitigation plan was developed. This included ongoing slope movement monitoring, regular site reconnaissance and placement of the pipeline above ground on “sleepers” to isolate the pipeline from the underlying creeping slope. To-date, these mitigations have been successful in reducing strain on the pipeline.