A THREE DIMENSIONAL CONTACT MODEL FOR SOIL-PIPE INTERACTION

One of the most common causes of collapse of pipelines crossing unstable slopes is the large deformation induced by landslides. This paper presents a numerical methodology based on the finite element method for the analysis of buried pipelines considering the nonlinear behavior of the soil-pipe interface. This problem is inherently complex since it involves the interaction between two different bodies (pipe and soil), and is affected by many elements such as material nonlinearities, local and global buckling, soil settlement, pipe upheaval, among others. An important aspect that should be considered in the study of buried pipes is the mechanical behavior along the interface between the structure and the soil. The contact problem, which includes both a normal and a tangential constitutive law, is formulated through a penalty method. The finite element model considers full three-dimensional geometry, elasto-plastic material behavior and accounts for the presence of large displacements and deformations. In Brazil transport of petroleum, gas and oil derivatives between refineries and the port tanking terminals that collect and export petroleum products is generally made through buried pipelines that cross the mountain range of Serra do Mar. These mountains run parallel to the Atlantic Coast and stand between the Brazilian plateau, where most of the largest cities are located, and the lower sea plains. A major concern during design and performance monitoring of these buried structures is the potential occurrence of soil movements, usually triggered by heavy rainfalls in areas lacking protective forest covering or those that have recently experienced changes of landscape caused by excavations, cuts and embankments due to road constructions, new industrial developments, etc. In cases of pipeline damage the consequences may be quite severe in terms of economical losses, social and environmental impacts.

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