Pipeline Modeling and Assessment in Unstable Slopes

The OCENSA pipeline system is exposed to different geotechnical problems, including faults, landslides and/or creeping slopes. These problems are typical of the Andes Mountains, especially in tropical countries like Colombia. Due to the fact that the system was constructed buried, the pipe interaction with the surrounding soil is a very important factor that must be taken into account in these unstable places in order to guarantee the pipe integrity. In this paper, a methodology to evaluate the pipe response under soil displacements in slow landslides is proposed. This methodology consists of three different cases of analysis, according to the characteristics of the place in study. It starts using a simplified analytical model and ends with 3D finite element numerical simulations using the real geometry of soil and pipe. The 3D continuum finite element models are made using the general purpose nonlinear software ABAQUS/Standard. These models are calibrated and validated with soil displacement data acquired from geotechnical instrumentation and pipeline geometry information obtained from in-line inspection tools. The models are used to predict the pipe behavior, estimating the moment at which the pipe overpasses the allowable strains. Based on the calculated strains, relief procedures are programmed and executed. These activities allow the pipeline to relieve the strain caused by soil movements, avoiding the occurrence of failures. For this reason, the proposed methodology is a very important tool in the OCENSA pipeline integrity program, which has been used successfully to assess the pipe condition in unstable areas and to take the appropriate remediation and mitigation techniques.