Nonlinear F.E.M. strategies for modeling pipe-soil interaction

H. KUNERT; J.L. OTEGUI; A. MARQUEZ; P. FAZZINI

Cambridge

Congreso; ICEFA 4, 4th Int. Conf. on Eng. Failure; 2010

This paper discusses the results of different finite element modeling strategies to assess the behaviorof pipelines buried in rainy forest regions, which are prone to failures by axial stresses from landmovement. Two failures had already been investigated; conclusions of Root Cause Analyses agreewith numerical predictions. The model allows quantifying soil displacements that load the system, aparameter that could not be estimated by geotechnical specialists. The model also confirmed otherfacts suggested by different failure analyses with no trivial theoretical demonstration, such as thenotable effect of pipe diameter.The tool is based on a three-dimensional simulation of the zone under analysis, which can beup to one kilometer long. The finite element method is used for the resolution of partial derivativedifferential equations and incorporates complex nonlinear physical-mathematical models, includingcontact algorithms and failure criteria at material level. A typical geometry considers a 20 m wideand up to 20 m deep right of way, supported in the solid rock layer. The ground is modeled withtetrahedral elements and their parameters describe different soil layers.An example is presented, in which two parallel pipelines of different diameter were modeledusing quadratic beam elements. The pipe-soil interaction effect is considered through a rigid linkage(a shared node) between the elements that model the pipeline and the elements that model the soil.The tool is properly adjusted using field instrument data and test results from the regionunder study, which include geotechnical measurements and pipe strains via vibrating wire straingauges. The tool is meant to assist the Line Operators in Integrity Management Policies.