Finite element modeling of time-dependent deformations in marine clays

Horst G Brandes, University of Rhode Island

Abstract

This study is part of a comprehensive program at URI that is investigating sediment deformation processes on submarine slopes. The work presented herein centers on developing a numerical capability for predicting the stress-strain-time behavior of fine-grained sediments that can be used to analyze deformation patterns observed on the continental margin.^ A new finite element code (GEO-CP) is presented which uses a realistic characterization of marine materials, including creep and time-dependent hardening. The constitutive model chosen is that of Borja and Kavazanjian which incorporates the widely used creep equations of Taylor and Singh-Mitchell. The GEO-CP program was derived from the code CRISP, and includes a number of significant improvements.^ The predictive capabilities of GEO-CP are examined in a unique long-term, drained, triaxial creep test conducted on an undisturbed sample of deep sea clay. In general, the predicted behavior during the early stages of deformation is dominated by the compressibility and drainage parameters, whereas the long-term behavior is most sensitive to the creep parameters. In the creep test used in this study, the model predicts the measured axial deformation very well.^ The program is also used to examine the pore pressure response in the triaxial specimen following the application of isotropic and deviatoric loads. Results show that for the low permeability marine clay the Mandel-Cryer effect is pronounced and results in large pressure gradients and non-uniform stress distributions. The effect of creep on pore pressure dissipation is to delay the rate at which it proceeds. In addition to laboratory settings, the program is put through verification runs that show close agreement with exact solutions when available. Overall, significant confidence has been gained in the code to serve as a useful tool in modeling field slopes.^ A discussion of the modeling approach for a particular cross-section of the continental slope south of New England centers on the various analysis options available. The specific finite element discretization scheme proposed involves a minimum of some 5,000 to 10,000 elements to achieve the kind of resolution observed in the acoustic profiles. Geologic evidence of downslope sediment deformation at other locations is also examined. ^

Subject Area

Engineering, Civil|Engineering, Mechanical

Recommended Citation

Horst G Brandes, "Finite element modeling of time-dependent deformations in marine clays" (1992). Dissertations and Master's Theses (Campus Access). Paper AAI9239546.
http://digitalcommons.uri.edu/dissertations/AAI9239546

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