A comparative study of different model families for the constitutive simulation of viscous clays

Abstract

Summary The simulation of the viscous behavior of some clays is of high importance in many geotechnical problems. The literature offers a vast amount of constitutive models able to simulate the rate dependence observed on these materials. Although most of these models are calibrated to very similar experimental observations and share similar definitions of material parameters, some discrepancies of their response have been detected, which are related to their mathematical formulations. In this work, the causes of these discrepancies are carefully studied. To that end, four different model families are analyzed, namely, nonstationary flow surface (NSFS) models, viscoplasticity with overstress function (OVP), viscoplasticity with Norton's power law (NVP), and visco‐hypoplasticity (VHP). For the sake of a fair comparison, single constitutive models using the same set of material parameters, and following other requirements, are developed for each model family. Numerical implementations of the four resulting models are performed. Their response at different tests are carefully analyzed through simulation examples and direct examination of their constitutive equations. The set includes some basic tests at isotropic stress states and others as responses envelopes, undrained creep rupture, and an oedometer test with loading, unloading‐reloading, creep, and relaxation. The article is concluded with some remarks about the observed discrepancies of these model families.

A high-cycle accumulation model for clay and its application to monopile foundations

“…Modified Cam Clay (MCC) model [11]), a hypoplastic model [46,74] or a barodesy model [50] for the simulation of a bearing capacity problem of a shallow foundation on clay. These models are only able to simulate monotonic loading for non-viscous clays, and as in detail discussed in [72], they would not capture the strain rate dependency typical for plastic clays (as is the case with soft marine clays). If the clay shows a high plasticity, a ratedependent model could be useful [10,86].…”

A simple hypoplastic model with loading surface accounting for viscous and fabric effects of clays

“…Specifically, while the viscous strain rate was semi‐implicitly integrated, other components of the models were explicitly computed. This required the computation of an algorithmic jacobian J alg , which is explained in detail in Tafili et al 27 Numerical integration of the models under different paths assuming element test conditions (homogeneous field for stresses and strains) was solved with the use of a Newton–Raphson solution scheme, whereby tolerances and a maximum number of iterations were specified to minimize the numerical error. During the calculations, no further numerical issues were detected.…”

“…Up to now, a relatively thorough understanding was implemented in constitutive models for time-independent fine-grained soils. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Some of these works are restricted to either normally consolidated 22 or overconsolidated 21 fine-grained soils. Some models need various parameter sets for different overconsolidation ratios, which for the users is very confusing.…”

“…Some models need various parameter sets for different overconsolidation ratios, which for the users is very confusing. In order to capture the strain-rate dependency typical for plastic clays, different models [27][28][29][30][31][32][33][34][35][36][37] have been developed. The majority of recent works in this field have opted for the viscoplastic strains to replace the original plastic strains in order to describe the time and strain rate effects observed in experiments with soft clays.…”

“…Up to now, a relatively thorough understanding was implemented in constitutive models for time‐independent fine‐grained soils 14‐28 . Some of these works are restricted to either normally consolidated 22 or overconsolidated 21 fine‐grained soils.…”