Nonlinear Constitutive Model of Stress-Strain Behavior for Bay of Campeche Sand-Paper

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The study calibrates the MRDF-UIUC nonlinear constitutive model in DEEPSOIL to predict the cyclic stress–strain behavior of Bay of Campeche sand. The calibration uses resonant-column and cyclic direct-simple-shear test data from 216 specimens, comprising 2,779 measurements of normalized shear modulus (G/Gmax) and material damping ratio across a range of strains and confining stresses.<br /><br />Regression analysis was used to establish the model’s ten parameters, several as functions of effective confining stress and others as constants. The calibrated model reproduces measured cyclic stress–strain loops closely when degradation caused by excess pore pressure is not considered. For G/Gmax values above 0.3 and damping ratios above 5%, predictions are generally within 30% of laboratory measurements. The model tends to overpredict at lower modulus and damping values, and its fit is poorer at large strains under higher confining stresses.<br /><br />The authors recommend limiting use of the calibration to effective confining stresses from 0 to 400 kPa. Within this range, it can support seismic site-response analyses and provide preliminary estimates of modulus-reduction and damping curves when dynamic laboratory testing is unavailable or insufficient. It is a supplement—not a replacement—for appropriate geotechnical investigation and dynamic testing.

Keywords

MRDF-UIUC

DEEPSOIL

Bay of Campeche sand

cyclic stress-strain behavior

normalized shear modulus

material damping ratio

resonant-column test

cyclic direct-simple-shear test

effective confining stress

seismic site-response analysis