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 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 analyses with no trivial theoretical demonstration, such as the notable effect of pipe diameter.The tool is based on a three-dimensional simulation of the zone under analysis, which can be up to one kilometer long. The finite element method is used for the resolution of partial derivative differential equations and incorporates complex nonlinear physical-mathematical models, including contact algorithms and failure criteria at material level. A typical geometry considers a 20 m wide and up to 20 m deep right of way, supported in the solid rock layer. The ground is modeled with tetrahedral elements and their parameters describe different soil layers.An example is presented, in which two parallel pipelines of different diameter were modeled using 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 region under study, which include geotechnical measurements and pipe strains via vibrating wire strain gauges. The tool is meant to assist the Line Operators in Integrity Management Policies.