This paper addresses the behavior of pipelines partially buried on clay soils under large displacements, which is one of the principal concerns in the design of HP-HT subsea pipelines with lateral buckling. Subsea pipelines are being required to operate at higher pressure and temperature (HP-HT) in recent projects developed in deepwater. Many of these projects adopt a design philosophy of controlled buckles by limiting feed-in displacement at the buckle locations. DNV OS-F101 contains a strain based design approach that has been frequently adopted by designers. The use of the strain based design approach implies in a careful evaluation of soil resistance during a lateral buckling process, because a small increase in this parameter can produce a significant increase in the strains at the buckle apex. In the recent years PETROBRAS has developed several projects in deepwater areas of the Santos and Campos Basins, offshore Brazil, where soft clay is predominant. This has motivated the development of an extensive experimental test program for pipe-soil interaction, aimed at increasing the design reliability of subsea pipelines with lateral buckling. The model presented is based on full scale tests developed at the Institute of Technological Research (IPT) installations over the last three years. The experimental results were used to develop a model for the lateral residual friction factor based on dimensionless groups that govern the problem. The aim of this model is to improve knowledge obtained by the industry in recent years, mainly by the JIP SAFEBUCK I and II programs. Furthermore, the full scale tests produced results for the breakout friction factor that were compared with a predicted pipe response based on models currently adopted in the industry. Moreover, some "very light" to "heavy" cyclic behavior highlights are presented and discussed. The model developed for the residual friction factor provides an important improvement especially for "heavy" pipes, where a gap was verified in deepwater pipeline design. A classification for "very light" to "very heavy" pipes is proposed, based on the experimental results and soil bearing capacity expressions from geotechnics. This classification is a very useful tool to understand pipe-soil behavior for large displacements.

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