Investigation of Seismic Response of Reinforced Soil Retaining Walls

Dynamic response of a segmental (modular block) retaining wall system to recorded ground motions is investigated. The magnitude and characteristics of wall response are compared to those obtained under harmonic input base acceleration. The calculated maximum lateral displacement and reinforcement load of the segmental retaining wall mode1 subjected to a single frequency, harmonic input acceleration were considerably larger than the corresponding values obtained using a number of earthquake accelerograms with comparable predominant frequencies. It is concluded that the random characteristic of actual ground acceleration may partly explain the relatively good performance of reinforced-soil retaining wall systems that were designed without seismic considerations or at best using simple pseudo-static limit equilibrium methods. Nevertheless, it was found that low-frequency ground motions with high intensity values can result in significant structural response magnitude of short-period retaining wall systems

Earthquake load attenuation using EPS geofoam buffers in rigid wall applications

The paper is a synthesis of previously published work by the authors that is focused on the use of expanded polystyrene (EPS) geofoam buffers for seismic load attenuation against rigid basement and soil retaining walls. The paper begins with a brief description of the first documented field application followed by a description of physical 1 m-high reduced-scale shaking table tests that provided the first proof of concept . Next, details of the development and verification of a displacement-based model and a FLAC numerical model are described and simulation results that were verified against the physical shaking table tests presented. The numerical results include simulations using simple linear elastic constitutive models for the EPS buffers and granular soil backfill and more complex non-linear hysteretic models. Finally, the verified FLAC model was used to develop a series of preliminary design charts for the selection of a suitable seismic buffer based on characteristics of the design earthquake accelerogram

Vertical facing panel-joint gap analysis for steel-seinforced soil walls

This paper reports the results of a numerical parametric study focused on the prediction of vertical load distribution and vertical gap compression between precast concrete facing panel units in steel-reinforced soil walls ranging in height from 6 to 24 m. The vertical compression was accommodated by polymeric bearing pads placed at the horizontal joints between panels during construction. This paper demonstrates how gap compression and magnitude of vertical load transmitted between horizontal joints are influenced by joint location along the height of the wall, joint compressibility, and backfill and foundation soil stiffness. The summary plots in this study can be used to estimate the number and type (stiffness) of the bearing pads to ensure a target minimum gap thickness at the end of construction, to demonstrate the relative influence of wall height and different material component properties on vertical load levels and gap compression, or as a benchmark to test numerical models used for project-specific design. The paper also demonstrates that although the load factor (ratio of vertical load at a horizontal joint to weight of panels above the joint) and joint compression are relatively insensitive to foundation stiffness, the total settlement at the top of the wall facing is very sensitive to foundation stiffness. This paper examines the quantitative consequences of using a simple linear compressive stress–strain model for the bearing pads versus amultilinear model that is better able to capture the response of bearing pads taken to greater compression. The study demonstrates that qualitative trends in vertical load factor are preserved when a more advanced stress-dependent stiffness soil hardening model is used for the backfill soil as compared with the simpler linear elastic Mohr–Coulomb model. Although there were differences in vertical loads and gap compressionwith the use of both soilmodels for the backfill, the differenceswere small and not of practical concern.Peer ReviewedPostprint (author's final draft

Shaking Table Methodology and Instrumentation for Reinforced Soil Retaining Walls

The paper describes a testing methodology, instrumentation array and example data interpretation for reduced-scale geosynthetic reinforced soil (GRS) wall models built on a large shaking table. The testing program is unique in the literature because of the large number of different instruments deployed and the use of Particle Image Velocimetry (PIV) analysis of imagery captured using a high speed camera. The models are instrumented with strain gauges and extensometers attached to the geogrid reinforcing layers, LVDTs attached to the facing panel, load cells at the wall toe, reinforcement-facing load measurement, and accelerometers in the backfill and along the facing. Example measurements are reported that demonstrate the value of the experimental technique to better understand the mechanics of these systems under simulated earthquake

Short-term thermo-mechanical numerical modelling of reinforced soil walls with polyester strap reinforcements

Polyester (PET) materials have become more common as reinforcement solution in reinforced soil walls (RSW). It has been shown that strength and stiffness of geosynthetics products, including PET, is load-, time-, and temperature-dependent. Consequently, the mechanical response of these materials is influenced by in-soil conditions. The present study describes viscoelastic and visco-plastic constitutive formulations used to model PET strap reinforcement layers in thermo-mechanical finite element models. The models are demonstrated using an idealized 15-meter high RSW with concrete facing panels, including loading due to a road at the top of the structure. Reinforcement model parameters were calibrated using laboratory measured data. Analyses include temperature boundary conditions representing a Mediterranean climate for a 1-year period following end of construction. Calculated stress and strain values were in accordance with values found in the literature. The results of this study are a precursor for the long-term modelling of RSWs under operational conditions subjected to changing atmospheric boundary conditions.The authors wish to thank Aaron Kim from GECO Industrial (Korea, Rep.) for providing polymeric strap data from manufacturing quality control records. The authors wish to acknowledge the support of the Department of Civil and Environmental Engineering (DECA) of the Universitat Politécnica de Catalunya�����BarcelonaTech (UPC) and the International Centre for Numerical Methods in Engineering (CIMNE) and the funding received from the Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S-20-4).Peer ReviewedPostprint (published version

Modeling soil-facing interface interaction with continuum element methodology

Soil-facing mechanical interactions play an important role in the behaviour of earth retaining walls. Generally, numerical analysis of earth retaining structures requires the use of interface elements between dissimilar component materials to model soil-structure interactions and to capture the transfer of normal and shear stresses through these discontinuities. In finite element method software programs, soil-structure interactions can be modelled using “zero-thickness” interface elements between the soil and structural components. These elements use a strength/stiffness reduction factor that is applied to the soil adjacent to the interface. However, in some numerical codes where the zero-thickness elements (or other similar special interface elements) are not available, the use of continuum elements to model soil-structure interactions is the only option. The continuum element approach allows more control of the interface features (i.e., material strength and stiffness properties) as well as the element sizes and shapes at the interfaces. This paper proposes parameter values for zero-thickness elements that will give the same numerical outcomes as those using continuum elements in finite element and finite difference commercial software. The numerical results show good agreement for the computed loads transferred from soil to structure using both methods (i.e., zero-thickness elements and continuum elements at interfaces). Both different interface modelling approaches can give very similar results using equivalent interface property values, and demonstrates the influence of choice of numerical mesh size on the numerical outcomes when continuum elements are used at the interfaces.Peer ReviewedPostprint (published version

Assessment of earth retaining wall sustainability: value functions and stakeholder weighting sensitivity

Earth retaining walls are common geotechnical structures with a wide range of solutions available to perform the same function. More and more, geotechnical engineers are asked to find the best solution among several options in different civil engineering applications based on environmental impact, cost and societal/functional issues. Evaluation of these three pillars during the selection process of a structure (such as an earth retaining wall) is called a sustainability assessment. This paper describes a sustainability assessment methodology and gives examples to select the best sustainable option from candidate conventional gravity and cantilever wall types, and steel and polymeric soil reinforced mechanically stabilized earth (MSE) walls of 5 m height. Analyses were carried out using the MIVES methodology which is based on value theory and multi-attribute assumptions. The paper identifies how indicator issues are scored, weighted and aggregated to generate final numerical scores that allow solution options to be ranked. The final scores include an adjustment based on stakeholder preferences for the relative importance of the three sustainability pillars (environmental, economic (cost) and societal/functional). The analysis results show that MSE wall solutions are most often the best option in each category compared to conventional gravity and cantilever wall solutions and thus most often the final choice when scores from each pillar were aggregated to a final score. The paper also includes a sensitivity analysis of the choice of value functions and stakeholder weighting preferences on the final ranking scores used to select the best sustainable solution. The analyses also show that the choice of value function and stakeholder preferences can lead to a conventional structure being the best option.Postprint (author's final draft

Simplified approach to analyse global stability of reinforced soil walls

Reinforced soil walls (RSW) are a proven alternative to conventional earth retaining structures due to their rapid construction, smaller environmental impact, lower cost, as well as more sustainable social/functional features. Design methods for RSW appear in international codes and guidelines. However, they often do not provide detailed calculations for global stability assessment. Global stability can significantly affect RSW design for specific geometric cases and/or site-specific boundary conditions. Traditional limit equilibrium (LE) methods have the disadvantage of not considering reinforcements and/or require iterations to achieve a safety factor (SF) value. Alternatively, numerical methods can be time consuming for both model generation, particularly for complex geometries, and during calculations. The present study discusses different analytical strategies using limit equilibrium formulations and a numerical finite element method, and proposes a simplified analytical method for global stability analysis based on a three-part wedge failure mechanism, and simple wall conditions.Peer ReviewedPostprint (published version

3D modelling of reinforced soil walls

This report summarizes the scope and conclusions of a 3D numerical modelling analysis of mechanically stabilized earth (MSE) walls constructed with concrete panels and strip reinforcement. These systems pose numerical challenges as a result of the discontinuous reinforcement arrangement which suggest the necessity on the 3D strategies instead of 2D modelling to determine and to fit its actual intrinsic behaviour.Postprint (published version

Rules and exercises on the right use of the Latin subjunctive mood; interspersed with observations to assist the learner in the acquisition of a pure Latin style.

Mode of access: Internet