Pipelines crossing mountainous areas are susceptible to ground movement loading from landslides. Structural analysis of pipeline performance from landslide loads is critical for making decisions on the requirement and timing of intervention activities. Current analytical assessment methodologies for pipelines affected by ground movement tend to assume the landslide as an abrupt boundary from the stable region to moving ground, causing an over conservative estimation of the condition of the pipeline. In-line inspection using inertial mapping tools provides invaluable information to assist in the determination of the current pipeline integrity but does not provide a complete picture because axial loads are not defined. Interpretation of in-line inspection data allows the estimation of a transition zone width between stable and unstable ground, where there is a progressive increase in ground movement. Due allowance for the transition zone can remove conservatisms in the assessment methodology and allow a pipeline integrity plan to be created. This paper investigates the influence of landslide transition zone dimensions on the pipeline response and a methodology is developed for the prediction of the transition zone width. The interaction between the ground and the pipe movement is modelled using finite element analysis techniques. The definition of the transition zone properties provides a more reliable prediction of the pipeline performance and enables the current and future pipe integrity to be established with greater confidence.

An analysis was performed of the charts that are traditionally employed in the determination of the separation of geotechnical protective structures on rights-of-way, such as cut-offs and trench barriers. An analysis was performed for the specific study area, with information from the existing weather and rainfall stations, which made it possible to characterize more accurately the rainfall figure required for curve fitting. Furthermore, knowledge of the soils in the area made it possible to classify them in terms of erodability. This classification was used to establish curves that better reflect the actual conditions of the soils of the rights-of-way. A conceptual analysis was performed of the need for the implementation of these structures in order to control erosion along the rights-of-way. This analysis made it possible to propose changes in the materials specification, in order to optimize costs during construction. As a supplement to the study of the protective structures for the rights-of-way, the dimensions of the trench for the installation of the pipelines was analyzed. This analysis included a comparison of the actual construction dimensions of the trench against the dimensions recommended by international standards and the ones contained in the international literature. Certain Colombian projects that supplement the analysis are also cited. The foregoing findings were used in the preparation of certain recommendations regarding the reduction of the dimensions of the trench for certain specific technical, social, and environmental conditions. Last, based on the analyses that were performed, the study proposes certain changes in the operator’s current standards, primarily regarding items such as cut-offs, trench barriers, and the dimensions of the trench. These changes will lead to a reduction in the construction costs of the geotechnical protective structures for hydrocarbon-pipeline rights-of-way. These items are typical, because the pipelines in question are located predominantly on foothill plains.

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.

To ensure the integrity of pipelines in failure mode Geotechnical, TRANSPETRO and the TBG perform underwater inspections of pipelines in the main crossings of rivers, lakes, dams, canals and permanently flooded areas. The inspections are designed to locate guideline and measure the covering the pipelines from the margins and underwater depth, identify any exposure of the pipelines, map the occurrences of blocks of rock or debris on the channel and evaluate the anthropic influence on stability of the sections inspected. Among the crossings rivers inspected, in the Atibaia V, with approximately 27.3 m in length, was observed a high erosive potential, which resulted in the loss cover of 3 (three) pipelines of crossing river, besides the fiber optic cable. The lengths uncovered resulted in approximately 33.0 m, with suspended pipes, damage in the concrete jacket and presence of blocks of rocks in the channel. The pipeline in the most critical situation went vain of 6.0 m, with gap up to 0,2 m in relation the background. The crossing river was studied with bathymetric survey and designed cover the pipelines with mechanical protection and anti-erosive. The pipes were supported with sacks of granular material, sequentially, the margins and pipelines were protected with geotextile filled with concrete, installed with the help of divers. The working conditions of 4.0 m depth, currents of up to 0.8 m/s, temperature and low visibility waters were challenges overcome during execution, in which the divers took turns in short periods. Due to the characteristics of the bedrock, the blankets went stylized and stitched on the field by the team, with dimensions taken on site. After positioning the blankets in the background began the underwater concreting, which occurred in stages monitored by the volume pumped and divers strategically placed. The crossing river was re-inspected approximately 1 (one) year after their stabilization and was found in good conditions. The occurrence improved the procedures for geotechnical monitoring and treatment of pipelines uncovered in crossings rivers, being who the efficiency and safety of the work performed currently serve as a reference for the design of similar works.