The response of dense sand to the ice gouging event

Nematzadeh, Afrouz (2019) The response of dense sand to the ice gouging event. Masters thesis, Memorial University of Newfoundland.

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Abstract

The integrity of subsea pipelines in the Arctic regions are threatened by ice-related subsea geohazard. A common practice for physical protection of the pipelines against the ice loads is to burying them inside the subsea trenches. However, determining the minimum burial depth of the pipeline to minimize the construction cost is a challenging design aspect of Arctic offshore pipelines. This requires an in-depth understanding of the ice-soil-pipe interaction, which in turn is significantly affected by ice-soil interaction and the foucuse of this thesis. Mohr-Coulomb soil model is conventionally used for continuum modeling of dense sand by adopting the constant friction and dilation angles. However, this approach neglects the pre-peak hardening and the post-peak softening behavior of dense sand. In this study, two smart self-correcting soil models were incorporated into an advanced Coupled Eulerian-Lagrangian (CEL) analysis to automatically update the shear strength parameters by the magnitude of plastic strains. The analysis was conducted using ABAQUS/ Explicit scheme incorporating the soil model that was coded into a user-defined subroutine. The soil strength parameters are self-corrected to model the nonlinear hardening, softening and pressure dependency behavior of dense sand by considering the ice keel bearing pressure and octahedral shear strain. The pre-peak hardening, and post-peak softening behavior of dense sand were captured through a series of free-field ice gouging analysis. Tow comprehensive parametric studies were conducted, one investigated the ice properties and anther one was foucued on the soil parameters.

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