Geohazard Risk Management for the Nor Andino Gas Pipeline

A 1,050 km long 20” pipeline was constructed to transport natural gas from northern Argentina to the coast of Chile. On the Argentine side, significant portions of the route traverse rugged mountainous terrain subject to landslides, debris flows, flash floods, and earthquakes. On the Chilean side (situated up to 5,000 m above sea level), the pipeline crosses active faults and terminates at locations historically subject to tsunami. The pipeline began operation in 1999. An outburst flood in a steep mountain stream caused the pipeline to rupture in 2001. Reactivation of a large rock slide in 2002 caused a second rupture. It appeared that the original design had underestimated the route’s exposure to geohazards, and efforts were required to improve pipeline safety and reliability. A geohazard risk management program was initiated in April 2002. Geohazards were identified and characterized through airphoto interpretation and field inspection. Sites were initially ranked using semi-quantitative risk estimates. Risk cost-benefit analyses were used to select optimal risk control measures at high ranking geohazard sites. These included monitoring programs, reconstruction of stream crossings, reroutes, and in one instance, landslide avoidance using a horizontal directional drill. Risk control measures were implemented between 2002 and 2006, and additional efforts are ongoing. An updated assessment of geohazard exposure was completed in 2005 with the objective of quantifying the level of risk reduction that had been achieved and prioritizing further risk reduction efforts. This paper describes implementation of the geohazard risk management program using a case history format. It highlights the techniques used to control the range of hazard that were identified in 2002 and to quantify the improvements achieved by 2006. The paper concludes with an overview of additional risk reduction initiatives that are in progress or under consideration.