A Fully Coupled Numerical Framework for Predicting Dynamic Behavior in Unsaturated Soils and Its Application to Embankment Seismic Analysis
Publication: International Journal of Geomechanics
Volume 24, Issue 7
Abstract
A soil–water–air fully coupled numerical framework is proposed to predict the deformation and hydraulic behavior of soils under different saturation states in response to dynamic loading. The proposed framework is developed based on the mixture theory of porous media and the governing equations are discretized with the finite-element method. The soil behavior is modeled by a sophisticated constitutive model. The hysteresis characteristic and the mutual dependence between volume change and the degree of saturation in the soil–water characteristic curve (SWCC) are considered. A consistent description for both unsaturated and saturated soils is achieved by taking the effective stress and the degree of saturation as the two independent variables, with only one set of unified mechanical/hydraulic parameters. The numerical framework is first validated at the element level against undrained and unvented strain-controlled cyclic triaxial test results of unsaturated Toyoura sand. The reliability of the proposed framework in addressing boundary value problems is further validated by the simulation of a dynamic centrifuge model test. The numerical framework is further applied to the dynamic stability analysis of unsaturated embankments with different initial water contents. The results show that initially unsaturated embankments with relatively high water content are susceptible to liquefaction during seismic loading. There is a significant correlation between the liquefaction and the deformation-induced soil saturation. Deformation-induced saturation initially occurs at the toe of the embankment and then gradually extends to the areas near the lateral surfaces of the embankment, which triggers the development of shear bands.
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Data Availability Statement
All data, models, and code generated or used during the study appear in the published article.
Acknowledgments
The authors wish to acknowledge the financial support from the National Natural Science Foundation of China (Grant Nos. 41727802 and 42072317) and the Science and Technology Commission of Shanghai Municipality (Funding No. 21DZ1204300).
Notation
The following symbols are used in this paper:
- bi
- body force;
- br
- parameter of anisotropy;
- c1
- fitting parameter shaping the drying boundary curve;
- c2
- fitting parameter shaping the wetting boundary curve;
- c3
- fitting parameter shaping the scanning curve;
- stiffness tensor;
- stiffness tensor in Hooke’s law;
- stiffness tensor related to the degree of saturation;
- elastoplastic stiffness tensor;
- e
- void ratio;
- f
- yield surface;
- κ
- swelling index;
- bulk modulus of water/air (α = w, a);
- intrinsic permeability of water/air (α = w, a);
- initial stiffness of the scanning curve;
- M
- stress ratio at the critical state;
- m*
- parameter related to structure;
- m
- parameter related to overconsolidation;
- N
- void ratio at NCL under reference state;
- N(Sr)
- void ratio at NCLS under reference state;
- n
- soil porosity;
- p
- mean stress on the subloading yield surface;
- mean stress on the superloading yield surface;
- mean stress on the normal yield surface;
- p0
- mean stress under the reference state;
- pr
- referenced mean stress;
- Qi
- interaction between the soil and air;
- q
- deviatoric stress on the subloading yield surface;
- deviatoric stress on the superloading yield surface;
- deviatoric stress on the normal yield surface;
- q0
- deviatoric stress under the reference state;
- Ri
- interaction between the soil and water;
- Sij
- deviatoric stress tensor;
- Sr
- degree of saturation;
- residual degree of saturation;
- saturated degree of saturation;
- s
- suction;
- sd
- SWCC parameter for the AEV on the drying boundary curve;
- sw
- SWCC parameter for the AEV on the wetting boundary curve;
- ua
- pore air pressure;
- uw
- pore water pressure;
- V
- integration domain in finite-element method;
- v
- Poisson’s ratio;
- β
- stress-induced anisotropic stress tensor;
- δ
- Kronecker’s delta;
- η
- stress ratio;
- stress tensor related to anisotropy;
- λ
- compression index;
- ρ
- average density of the mixture;
- intrinsic density of soil/water/air (α = s, w, a);
- partial density of soil/water/air (α = s, w, a);
- σij
- total stress tensor;
- soil skeleton stress tensor; and
- ζ
- magnitude of anisotropy.
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Received: Apr 24, 2023
Accepted: Jan 14, 2024
Published online: May 7, 2024
Published in print: Jul 1, 2024
Discussion open until: Oct 7, 2024
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