Results of a Mitigation Technique Used to Reduce Pipeline Strains in Unstable Slopes

Abstract

The OCENSA pipeline system crosses a wide range of geological zones, finding different stability problems. Those problems related with landslides are stabilized with different kinds of geotechnical works within the pipeline maintenance programs, but sometimes these problems reach big dimensions making very difficult to stabilize them, so mitigation techniques are necessary in order to guarantee the pipe integrity. A mitigation technique using EPS (Expanded Poly-Styrene) blocks is being used in the OCENSA pipeline system (Colombia) in order to reduce the buried pipe response due to soil displacements during landslide events and in creeping slopes. OCENSA is the first operator in Latin America using this technique. Prior to the use of this technique, numerical modeling studies were done with the support of SOLSIN S.A.S. These studies were focused on determining the viability and effectiveness of the proposed technique. The purpose of the EPS blocks is to constitute a low-density fill with very low Young modulus reducing the soil-pipeline interaction forces. These blocks are located near the landslide limits in both, the stable and un-stable zones in order to reduce the stiffness of the materials around the pipe. These blocks allow the pipe to move beyond the landslide limits, reducing the bending strains. The extension of the EPS backfill is determined by means of the geotechnical investigation of the place in study and using the in-line inspection tools data to determine the length of the pipe affected by the soil movement. In this paper, three case studies are presented in which the proposed mitigation technique effectiveness was proved. In this part, data analyses coming from the in line inspection program was done. The inertial tool data showed that the EPS blocks had a significant effect on the pipe response, reducing the total strains compared with those obtained with a normal backfill. This technique can be used to reduce the frequency of the strain-relief excavations in unstable slopes. That means a cost reduction in the pipe maintenance activities and a more efficient integrity management program.