| Owing to the highly nonlinear
behaviour of soil materials, pipe/soil interface phenomena, and the possibility of pipe
distortion, buried pipe/soil systems have a relatively complex behaviour. Two basic
approaches are used for numerical modelling of buried pipelines: (1) the
state-of-practice, using specialized beam type elements for the pipe and Winkler type
representation of surrounding soil (soil spring structural models) , and (2) the
state-of-the-art, using continuum finite element or boundary element methods.
The first approach is considerably less computationally demanding than continuum modelling methods. However, soil representation by nonlinear springs lacks physical significance and has serious limitations related to modelling of soil plastic, dilatational and hysteretic behaviour, and of shear interaction between different soil zones along the pipe. Plasticity soil constitutive models implemented in continuum finite element codes account for the true 3D stress state and are based on constitutive equations derived from observed soil behaviour. Another drawback of the structural approach is the inability to capture the details of pipe behaviour, such as ovalization and buckling. These aspects can also be addressed by the continuum approach.
A continuum finite element model for pipe-soil interaction involving large relative displacements was developed using the code ABAQUS Standard. The analysis procedure accounts for the nonlinear behaviour of soil and pipe materials, relative slip and separation at the pipe-soil interface, and ovalization and buckling of the pipe. The model was calibrated and validated based on full scale experimental data.
A series of aspects of pipe/soil interaction are not addressed by the standards used in current practice. Some of these aspects have been studied to provide guidelines for improving existing soil spring based structural models: soil failure mechanisms, including strain hardening and softening; trench effects; pipe ovalization and post-buckling behaviour; effects of internal pressure; effects of complex loading, etc.
To see some of these results, please click the links at the top-left of this page.