Nonlinear FEM strategies for modeling pipe-soil interaction

Abstract

This paper discusses the results of one finite element modeling strategy to assess the behavior of pipelines buried in rainy forest regions, which are prone to failures by axial stresses from land movement. Two failures had already been investigated; conclusions of Root Cause Analyses agree with numerical predictions. The model allows quantifying soil displacements that load the system, a parameter that could not be estimated by geotechnical specialists. The model also confirmed other facts suggested by different failure analysis with no trivial theoretical demonstration, such as the notable effect of pipe diameter. The model is based on a three-dimensional simulation of the zone under analysis, which can be up to 1 km long. The finite element method is used for the resolution of partial derivative differential equations and incorporates complex nonlinear physical-mathematical models. A typical geometry considers a 20. m wide and up to 20. m deep right of way, supported in the solid rock layer. Two sufficiently documented events were used to verify if the tool really reproduces the stress state in the pipe due to soil movements. The model is properly adjusted using field instrument data and test results from the region under study, which include geotechnical measurements and pipe strains via vibrating wire strain gauges. The tool is meant to assist the Line Operators on the Integrity Management Policy.