This paper presents an experimental study of shaking table tests on two back-to-back mechanical stabilized earth (MSE) walls with different width-to-height ratios (RWH) of RWH = 1.6 and 1.1, to ...investigate the influence of RWH on the dynamic response. The reduced-scale MSE wall models were designed according to the similitude relationships considering model geometry, reinforcement stiffness, and input motions. The back-to-back MSE wall models were constructed using poorly graded backfill soil and geogrid reinforcement, and then were excited using a series of sinusoidal input motions with increasing acceleration. Results indicate that the incremental facing displacements and residual facing displacements of the two back-to-back MSE walls increase significantly with increasing input acceleration. For the back-to-back MSE walls with RWH = 1.6, the predominant facing deformation mode is rotation for smaller input acceleration. However, the deformation mode becomes bulging with the highest displacement near the mid-height for higher accelerations. For the back-to-back MSE walls with RWH = 1.1, the predominant facing deformation mode is rotation during shaking. Back-to-back MSE walls with small RWH exhibited better seismic performance under the same input motions.
As a new technique, a fixed geogrid in a geogrid-reinforced and pile-supported (GRPS) embankments has been used to reduce the total and differential settlement. To investigate the load transfer ...mechanism of the fixed geogrid technique of a GRPS embankment, three discrete element method (DEM) models of pile-supported embankments were established, including an unreinforced embankment, a geogrid reinforced embankment, and a fixed geogrid reinforced embankment. The efficacy of the pile, the evolution law of the contact force chain and the axial force of the reinforcement, and the microscopic load-bearing structure of the soil were investigated. Numerical simulation results showed that the embankment self-weight and surcharge load were transferred to the pile through the soil arching and tensile membrane effect. The settlement could be effectively reduced via the addition of the reinforcement, and the fixed geogrid technique was more conducive to improving the load-bearing ratio of the pile than the traditional reinforcement technique. Compared with the traditional technique of a GRPS embankment, the fixed geogrid technique had a better effect on reducing the total and differential settlement. With the increase in the surcharge load and the settlement of the soft subsoil, the reinforcement transferred a greater load to the pile. The results also showed that the stress of the embankment fill was concentrated at the pile top in all three models. The GRPS embankment with a fixed geogrid technique had a lower soil stress concentration than the other two cases. The contact force chain and stress in the embankment also showed that the reformation of the microscopic load-bearing system of the embankment fill was the internal mechanism that caused the development of the soil arching and the redistribution of stress. Furthermore, the evolution of the fabric parameters in the arching area could reflect the evolution of the soil arching structure. In the fixed geogrid case, the proportion of the load transferred to the pile from the soil arching effect was reduced, and the vertical load transferred to the pile top by the tensile membrane effect accounted for 22–28% in this study. Under the combined effect of the tensile membrane and the soil arching, the efficacy of the pile could increase by 10%.
This paper presents an experimental study on the anisotropic shear strength behavior of soil–geogrid interfaces. A new type of interface shear test device was developed, and a series of soil–geogrid ...interface shear tests were conducted for three different biaxial geogrids and three different triaxial geogrids under the shear directions of 0°, 45° and 90°. Clean fine sand, coarse sand, and gravel were selected as the testing materials to investigate the influence of particle size. The experimental results for the interface shear strength behavior, and the influences of shear direction and particle size are presented and discussed. The results indicate that the interface shear strength under the same normal stress varies with shear direction for all the biaxial and triaxial geogrids investigated, which shows anisotropic shear strength behavior of soil–geogrid interfaces. The soil–biaxial geogrid interfaces show stronger anisotropy than that of the soil–triaxial geogrid interfaces under different shear directions. Particle size has a great influence on the anisotropy shear strength behavior of soil–geogrid interfaces.
This paper presents a numerical study on the investigation of microscopic mechanism governing the interaction of woven geotextile and angular sand employing the 3D discrete element method (DEM). The ...surface texture and tensile properties of the geotextile were simulated using overlapping spherical particles, and the angular sand was simulated using rigid blocks. The DEM models were fully calibrated based on previous experimental data. The shear and dilation zones of sand near the interface were quantitatively determined based on particle displacement gradients. Analysis of contact forces was conducted to explain the microscopic mechanism behind the macroscopic strength evolution. The influence of geotextile surface roughness on the shear strength of the geotextile-sand interface is also discussed. The results show that the failure mode of the woven geotextile-sand interface is a combination of particle sliding failure along the geotextile surface and shear failure of the sand within the shear zone above the interface. There is a rapid redistribution of contact forces prior to reaching peak shear resistance, and the average normal contact force within the shear zone remains relatively constant after the peak shear stress is achieved. A completely developed shear zone stabilizes soil deformation, typically after achieving the peak shear resistance.
•The thickness of the stabilized shear zone decreases as the normal stresses increase.•The shear zone is completely developed after the peak shear resistance is reached.•Contact forces are rapidly redistributed prior to reaching peak shear resistance.•The evolution of shear strength is caused by interparticle sliding in the shear zone.
This paper presents numerical simulations to investigate the influence of secondary reinforcements on the behavior of geosynthetic reinforced soil (GRS) walls under static loading. Simulations were ...conducted using a finite difference program to model an instrumented field GRS wall with secondary reinforcements. Simulated results are in good agreement with field measurements, including facing displacements, lateral soil stresses, and tensile strains of the primary and secondary reinforcement. A parametric study was then conducted to investigate the influences of secondary reinforcement length, backfill soil friction angle, and wall height on the static behavior of GRS walls with secondary reinforcements. Results indicate that the maximum facing displacement and the required reinforcement tensile force of primary reinforcements generally decrease with increasing secondary reinforcement length up to a critical value. The decreasing effect is more pronounced for GRS walls with lower soil friction angle and higher wall height. The K-stiffness method is overconservative for the calculation of required tensile force of primary reinforcements for GRS walls with secondary reinforcements, and the overestimation increases with increasing secondary reinforcement length. A design method that accounts for the influence of secondary reinforcements on the internal stability of GRS walls is provided.
•The influence of secondary reinforcements on the static behavior of GRS walls with is evaluated in terms of facing displacements and reinforcement tensile forces.•The influences of backfill soil friction angle and wall height on the behavior of GRS walls with secondary reinforcements are investigated.•The calculated required reinforcement tensile forces using the FHWA design method are evaluated and compared with the simulated results.•A design calculation method that accounts for the secondary reinforcement length on internal stability of GRS walls is provided.
A three-dimensional discrete element method (DEM) model was developed to explore the influences of shear direction and geogrid anisotropy on the shear strength behavior of geogrid-soil interfaces. In ...the DEM model, the anisotropic tensile behavior of biaxial geogrid was simulated using double-layered bonded spheres, and the irregular soil particle shapes were also considered. The DEM model for geogrid-soil interfaces subjected to shear in different directions was validated using experimental data. The tensile force development of geogrid ribs and the evolution of microstructure of the soil particles were presented and discussed. Results show that the interface shear strength in the 45° shear direction is the highest due to the passive resistance from both the longitudinal and transverse ribs. The evolution of microstructure of the soil particles indicates that the shear direction has a certain influence on the amplitude of normal contact force but little influence on the principal direction. The interface shear strength generally decreases with increasing anisotropy of biaxial geogrid due to the decrease of overall geogrid strength. The anisotropy of biaxial geogrid has an important influence on the geogrid rib passive resistance but little influence on the geogrid surface frictional resistance.
Corrosion-induced deterioration of material properties can noticeably affect the seismic performance of coastal reinforced concrete (RC) bridges in aggressive marine environments, causing significant ...adverse economic and environmental consequences post extreme events. This study systematically investigates the time-dependent seismic performance, resilience, and sustainability of coastal RC bridges. For that purpose, a three-dimensional (3D) nonlinear finite element (FE) framework is developed and combined with the formulation of performance-based earthquake engineering (PBEE) and an economic input-output life cycle assessment (LCA) approach. Seismic resilience and robustness of the coastal RC bridges are subsequently evaluated in terms of the post-earthquake repair cost, repair time, and carbon footprint quantified by CO2. Within this framework, additional analyses are conducted to explore possible retrofit measures, including the use of fiber-reinforced polymer (FRP) reinforcement on the sustainability and resilience of the retrofitted RC bridges. For the presented scenario, it is shown that wrapping bridge columns with FRP composites can effectively increase the moment capacity, thus improving resilience and sustainability by reducing as much as 650 Mg of CO2 for this specific bridge. Overall, the derived insights highlight the need for sustainability, resilience, and potential retrofit analysis of coastal RC bridges in seismically active regions affected by corrosion-induced deterioration.
•A nonlinear 3D FE framework for coastal RC bridges is developed and combined with the PBEE formulation and EIO-LCA approach.•Seismic resilience and sustainability of RC bridges under aggressive marine environments and earthquakes are investigated.•Effectiveness of FRP composites to potentially enhance the performance of bridge columns is thoroughly explored.•Wrapping coastal bridge columns with FRP composites can effectively improve seismic resilience and sustainability.
Coastal bridges are particularly prone to damage caused by prior earthquakes, rendering them more vulnerable to subsequent hazards. The potential occurrence of a near-field tsunami can significantly ...exacerbate this damage, leading to detrimental environmental and economic impacts. Aiming to quantitatively assess these consequences, this study delves into the multihazard resilience and sustainability of a typical coastal Reinforced Concrete (RC) bridge under sequential earthquake-tsunami events. As such, a nonlinear three-dimensional (3D) finite element (FE) framework is established, seamlessly merging the economic input-output life cycle assessment (EIO-LCA) methodology with the principles of performance-based earthquake engineering (PBEE). To minimize the uncertainty in the probabilistic seismic demand model and the subsequent PBEE outcomes, an optimal intensity measure is chosen based on a comprehensive evaluation of efficiency, correlation, and coefficient of variation. Consequently, the multihazard resilience of the coastal RC bridge is assessed according to the repair time, repair cost, and carbon footprint. It is shown that bridges are more vulnerable under sequential earthquake-tsunami events compared to earthquake events alone, leading to notably increased carbon footprints and reduced resilience levels. Overall, the developed framework enhances the assessment of coastal RC bridge performance, providing valuable insights into the consequences for both the environment and socioeconomic aspects resulting from bridge damage during sequential earthquake and tsunami events.
•A framework for multihazard analysis of coastal RC bridges is developed by integrating FE modeling, PBEE, and EIO-LCA approach.•An optimal intensity measure is identified by considering correlation, efficiency, and coefficient of variation.•Multihazard resilience and sustainability of a coastal RC bridge during earthquake-tsunami sequential events is investigated.•Increased bridge susceptibility under earthquake-tsunami events causes increased carbon footprint and decreased resilience.
The stress-induced anisotropy of sand significantly affects the liquefaction susceptibility. This study systematically investigates the undrained behavior of saturated sand under both monotonic and ...cyclic loading through a series of torsional shear tests, considering the effects of initial anisotropic consolidation states, including extensional and compressional consolidation states. Special attention is paid to the evolution of effective stress paths, deformation pattern, pore water pressure generation, and the rotation of the principal stress direction during the torsional shear process. The experimental results show that specimens under different initial stress states and loading conditions exhibit two typical failure modes, i.e., residual strain accumulation and cyclic mobility. The evolutions of principal stress direction under both monotonic and cyclic loading are presented, which can provide useful insights into the underlying mechanism of the occurrence of different failure modes. Based on the experimental results, a new index, unified cyclic stress ratio (USR), is proposed by correlating the number of cycles required for failure (Nf) with the initial anisotropic stress state and the shear strength at the phase transformation point. The proposed index USR can serve as a unified criterion for the evaluation of liquefaction resistance of sand considering anisotropic consolidation conditions.
•Monotonic and cyclic torsional shear tests with different stress-induced anisotropy for saturated sand are conducted.•The monotonic stress path can serve as a boundary for the evolution of the cyclic stress path under same anisotropy states.•The impact of stress-induced anisotropy on the cyclic resistance is explained by the rotation of principal stress axis.•A new index is provided by linking the failure cycles to the consolidated stress ratio and phase transform strength.
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