Fang-Le Peng

FEM simulation of deformation and strength characteristics in geogrid- reinforced sand retaining wall under the change of loading rate

It is often important in geotechnical engineering practice and research to evaluate accurately the time effect on the deformation and strength characteristics of geogrid-reinforced sand retaining wall. Loading rate effect is one of the most important time-dependent behaviors of material, which is an inherent response of the viscous property of material. Based on the Dynamic Relaxation method, the nonlinear finite element method (FEM) analysis technique was developed. In the numerical analysis, both the viscous properties of the backfill (sand) and the reinforcement (geogrid) were taken into account through the unified non-linear three-component elastic-viscoplastic model. The presented FEM is validated by simulating a physical model test on geogrid-reinforced sand retaining wall. It is shown that the aforementioned FEM can well simulate the deformation and strength behaviors of geogrid-reinforced sand retaining wall under the change of loading rate, such as the overall footing pressure - settlement relationship and the earth pressure.

Simulating the Viscous Behavior of Sandy Ground by FEM

Dense sand exhibits very distinct viscous characteristics, as indicated by a number of plane strain compression tests. The main viscous aspect of sand lies in the effect of the strain rate change, creep and stress relaxation. Testing results show that the stress-strain relation is only temporarily disturbed by the change of strain rate and the viscous effect decays as loading progresses. To properly simulate the viscous characteristics, especially the temporary effect of strain rate change, a new visco-elastoplastic constitutive model is proposed for sand in this study, based on the three-component model framework. The model comprises of the hypo-elasitc, energy-based non-associated plastic and rate-dependent viscous components. Finite element simulations were conducted to model the viscous behavior of sandy ground under strip footing in the pre-peak strength realm under plane strain condition. Comparisons between physical test and numerical simulation results show that the proposed model is capable of capturing the viscous characteristics observed in the physical model experiments.

FEM analyses on creep characteristics and strain fields of geogrid-reinforced sand

ABSTRACT Both sand and polymer geogrid reinforcement are known to exhibit more-or-less complicated stress-strain-time or load-strain-time behavior including instantaneous non-linearity and viscous effects. Creep is one of the most important time-dependent behaviors of material, which is an inherent response of the viscous property of material. Due to interactions between the viscous sand and reinforcement, the creep characteristics of geogrid-reinforced sand could be very complicated. A nonlinear finite element method (FEM) analysis technique incorporating the unified three-component elasto-viscoplastic constitutive model for both sand and geogrid was developed. The FEM can simulate the whole process including the constant strain rate loadings and the creep loading stages. In addition, the development of strain fields during the creep loading can also be reproduced by the FEM simulation. By comparing the simulated results with the experimental results, it was shown that the proposed elasto-viscoplastic FEM could well simulate the creep characteristics of geogrid-reinforced sand, especially for the high stiffness following a creep loading stage.

Numerical Study on the Deformation and Failure of Reinforced Sand Retaining Walls Subjected to the Vertical Load

To gain a better insight into the deformation and failure of reinforced sand retaining walls subjected to the vertical load from the crest and their associated reinforcing mechanisms, the model experimental results from well-controlled fully-instrumented load tests of full-scale reinforced sand retaining wall with sand backfill are simulated by making use of a nonlinear elasto-plastic finite element model considering strain localization. In the finite element method (FEM) analysis, the effects of the following factors for the filled sandy soil are taken into account: (a) the non-linear pre-peak work-hardening and post-peak work-softening; (b) effects of stress history and stress path; (c) the confining pressure dependency and strength anisotropy; (d) the stress-dilatancy characteristics; and (e) strain localization into a shear band(s) with a width proportional to the particle size. The load-settlement relationship obtained from FEM analysis is generally in good agreement with the physical experimental result. It is also found that the progressive failure with a development of shear bands and the horizontal earth pressure on the back of facing and the tensile force in the reinforcement layers can be reasonably simulated by the proposed FEM analysis.

Simulating Rate-Dependent Behavior of Geogrid-Reinforced Sands by FEM

ABSTRACT A nonlinear finite element method (FEM) analysis technique incorporating the non-linear three-component elasto-viscoplastic constitutive models for both sands and polymer geogrids is developed. The model can describe the viscous effects on the stress-strain or tensile load-strain behavior observed in a series of comprehensive laboratory tests on clean sands or geogrids. The dynamic relaxation technique combined with the return mapping algorithm is applied to the inte gration algorithms of viscoplastic constitutive relations, including the effects of loading rate, stress path and shear band. A series of plane strain compression (PSC) tests performed on geogrid-reinforced sands were simulated by the FEM. The simulated average stress ratio and vertical strain relations of geogrid-reinforced sands were compared with the measurements. It is shown that the developed FEM analysis method can simulate the test results very well, especially for loading rate effects, creep and stress relaxation.

Elasto-Viscoplastic Simulation of Bearing Capacity Characteristics of Strip Footing on Reinforced Sand

A nonlinear FEM analysis incorporating an elasto-viscoplastic constitutive model for sand that has been developed based on results from comprehensive laboratory stress-strain tests including plane strain compression tests is described. A series of plane strain laboratory model tests on the bearing capacity on a model strip footing (10 cm -wide) performed on unreinforced and reinforced level sand grounds were simulated by the FEM. The simulated footing load and settlement relation and failure mechanism in the unreinforced and reinforced sand grounds were compared with the measured ones. It is reported that the proposed FEM analysis method can simulate very well the test results, including the effects of reinforcing. It is one of the characteristic features of the proposed numerical analysis method that the footing and settlement behaviour around the peak footing load state and the one in the post-peak regime can be simulated in a very stable manner. It is shown that this is due largely to that the realistic viscous properties of sand that are properly modeled are incorporated in the FEM analysis.