Mechanically Stabilized Earth Wall Design Research Articles

Analysis of the maximum reinforcement loads of four MSE walls compared to the values predicted by the AASHTO 2020 specification

Mechanically stabilized earth (MSE) systems are a well-known and applicable solution for retaining walls, that presents a composite structure consisting of layers of backfill soil with rigid or flexible reinforcement inclusions. The stability of the wall system is derived from the interaction between the backfill and soil reinforcements involving friction and tension. The wall facing has as its main function to prevent erosion of the structural backfill. The design of MSE walls is usually divided in two phases: external and internal stability. Although there are many methods to design MSE walls, the Coherent Gravity Method is the most common used for MSE walls reinforced with inextensible (steel) reinforcements, the Simplified Method for both steel and geosynthetics reinforced wall systems and the new one included in 2020, Stiffness Method, to calculate the maximum reinforcement loads, Tmax, for extensible (geosynthetics) reinforced MSE walls (all these methods are outlined in Section 11 of the AASHTO LRFD Bridge Design Specifications 2020) . The main objective of this paper is to carry out the analysis of the 3 methods available at AASHTO and compare the results from full-scale MSE walls and the predicted Tmax values.

Dynamic analysis of MSE wall subjected to surface vibration loading

Abstract Extensively used Mechanically Stabilized Earth (MSE) walls in Rail Transportation System (RTS) are vulnerable to surface vibrations generated by moving vehicles. Hence, it is necessary to consider the effects of surface vibrations during the design of MSE walls for RTS. Steel-reinforced panel-type MSE walls are shown to perform well during vibration loading, but costly steel materials have led to greater reliance on affordable and readily available geosynthetics for reinforcement. Limited research exists on the behavior of panel-type MSE walls with geosynthetics considering RTS-induced vibrations frequencies. Thus, this study employs Finite Element software PLAXIS 3D to simulate the impact of surface vibration frequencies on panel-type MSE walls. The qualitative study encompasses two reinforcement cases (geogrids and steel strips) of 4 m MSE wall height and four harmonic loading frequencies representing RTS-induced surface vibrations for simulation. The dynamic responses of MSE wall are presented in terms of lateral wall displacements and lateral earth pressure distributions. Furthermore, the distributions of tensile strain and the identification of potential slip surface locations are presented. The findings indicated that MSE wall and reinforcement responses are governed by RTS-induced vibrations and fundamental frequency of backfill soil. This highlights the need for consideration of both the fundamental frequency of the backfill soil and RTS-induced vibrations in the design of MSE walls.

Assessment of Soil–Structure Interaction Approaches in Mechanically Stabilized Earth Retaining Walls: A Review

Mechanically stabilized earth (MSE) walls are recognized for their cost-effectiveness and superior performance as earth-retaining structures. The integration of internally reinforced walls has transformed soil preservation practices, garnering significant attention from the global technical community. The construction method of MSE walls has recently gained widespread popularity, likely due to its cost efficiency and simplicity compared to traditional externally reinforced walls. This paper provides a comprehensive review of MSE walls, including their historical development, aesthetics, benefits, drawbacks, factors influencing lateral displacements and stress responses, and the concept of the MSE wall system. Key approaches for analyzing seismic soil–structure interaction (SSI) issues are emphasized, investigating the dynamic interaction between the structure and soil through various research methodologies. This study incorporates multiple publications, offering an in-depth review of the current state of dynamic SSI studies considering surrounding structures. The findings emphasize the significant sensitivity of the dynamic behavior of mechanically stabilized earth (MSE) walls to soil–structure interaction, highlighting the necessity for continuous research in this area. The paper identifies research gaps and proposes future directions to enhance MSE wall design and application, facilitating further advancements in earth-retaining structures.

Factors affecting the deformation of facing elements for MSE wall design

The deformation of the Mechanically Stabilized Earth (MSE) walls is one of the key factors which control the design of the MSE walls. In many practical cases, the size of facing panels concrete bedding is increased for high MSE walls. In the present study the effect of the dimensions and stiffness properties of the facing panels concrete bedding on the deformation of the facing elements and the axial forces developed in the geogrid reinforcements are analysed and discussed. The study has been conducted using a finite element analysis Plaxis-2D. The used model has been verified with data attested in the references, [1]. The geometry of model consists of MSE wall with precast concrete facing panels to support reinforced soil zone. The results shed the light on the influence of the dimensions and stiffness properties of facing panels concrete bedding on the deformation of the MSE facing panels. The results showed that for the cases considered in the study, increasing the width dimension of facing panels concrete bedding will decrease the deformations of the facing elements without significant changes in the axial forces developed in the geogrid reinforcing elements.

Multi‐objective optimization of mechanically stabilized earth retaining wall using evolutionary algorithms

AbstractThis paper uses evolutionary optimization algorithms to study the multi‐objective optimization of mechanically stabilized earth (MSE) retaining walls. Five multi‐objective optimization algorithms, including the non‐dominated sorting genetic algorithm II (NSGA‐II), strength Pareto evolutionary algorithm II (SPEA‐II), multi‐objective particle swarm optimization (MOPSO), multi‐objective multi‐verse optimization (MVO), and Pareto envelope‐based selection algorithm II (PESA‐II), are applied to the design procedure. MSE wall design requires two major requirements: external stability and internal stability. In this study, the optimality criterion is to minimize cost and its trade‐off with the factor of safety (FOS). To this end, two objectives are defined: (1) minimum cost, (2) maximum FOS. Three different strategies are considered for reinforcement combinations in the numerical simulations. Moreover, a sensitivity analysis was conducted on the variation of significant parameters, including backfill slope, wall height, horizontal earthquake coefficient, and surcharge load. The efficiency of the utilized algorithms was assessed through three well‐known coverage set measures, diversity, and hypervolume. These measures were further examined using basic statistical measures (i.e., min, max, standard deviation) and the Friedman test with a 95% confidence level.

Mobilized Bearing Capacity Analysis of Global Stability for Walls Supported by Aggregate Piers

Global stability analysis is a key component of mechanically stabilized earth (MSE) wall design, especially those constructed over marginal soils. When limit equilibrium analysis is used for MSE wall design, incorrect factors of safety can be predicted depending on the shape assumed for the failure surface. The use of ground improvement, such as aggregate piers (AP), further complicates the analysis. A mobilized bearing capacity (MBC) approach is presented which highlights the direct relationship between the factors of safety for global stability and bearing capacity. Results from the MBC approach are compared with finite element strength reduction analyses for a range of MSE wall geometries and AP replacement ratios. The factors of safety match well for global factors of safety between 1 and 1.5, considering both eccentricity and stress concentration. The MBC approach provides a tool to supplement and refine global stability analyses for retaining walls constructed over improved foundations.

Laboratory Pullout Test of Geogrid Reinforcements for Submerged Mechanically Stabilized Earth for Waterfront Applications

The design and evaluation of mechanically stabilized earth (MSE) wall structures for riverbank protection, quays, sea walls and other waterfront structures is critically dependent on a design parameter called the interaction coefficient (Ci) for submerged or fully saturated condition. However, the available research works conducted in this field are limited to non-submerged and, at most, partially saturated condition. This limitation does not closely represent actual conditions where waterfront structures are almost often submerged and fully saturated. Hence, the objective of this study was to determine the Ci in a submerged condition, on top of the Ci in a non-submerged condition for different types of geogrid reinforcement for fine-grained soils and coarsegrained soils used for MSE walls. Test results revealed that the Ci decreased as the effective overburden stress increased. The submerged conditions yielded lower Ci compared with non-submerged conditions, and the reduction wassignificant at a lower effective overburden stress for high density polyethylene uniaxial geogrid than the polyvinyl coated polyester yarn. The design parameters derived from these conditions can be used for the evaluation and design of MSE walls for waterfront applications with a higher level of confidence.

System Reliability Framework for Design of MSE Walls for Vertical Expansion of MSW Landfills

In the past few decades, waste generation has increased significantly in India, as well as across the globe. Therefore, to avoid the acquisition of new landfill sites, vertical expansion of existing municipal solid waste (MSW) landfills is a requirement of the present scenario. Owing to the heterogeneous nature of waste and varying degrees of decomposition in MSW, the conventional practices to calculate safety margins may not be suitable to handle the variability of the design parameters. Therefore, a system reliability framework is proposed for the optimum design of mechanically stabilized earth (MSE) retaining walls against external failure modes. The properties associated with MSW landfills, their foundation soil, and MSE walls are considered as random variables. The overturning, sliding, and bearing capacity failure modes are considered using a three-part wedge mechanism. The design charts are provided to obtain the adequate length of the reinforcement and the dimensions of the MSE wall. For satisfactory performance of the MSE wall, the minimum ratio of the length of the reinforcement to the height of the MSE wall should be 0.55 to 0.6 when an additional waste mass is placed on the existing height of the landfill.

Geosynthetic reinforcement stiffness characterization for MSE wall design

Reinforcement stiffness is a key parameter that influences the magnitude of tensile loads in geosynthetic mechanically stabilized earth (MSE) walls under operational conditions. An estimate of reinforcement creep stiffness at 2% strain and 1000 h is required to carry out internal stability design using the Simplified Stiffness Method. This paper provides equations that can be used to estimate the reinforcement creep stiffness based on the tensile strength for different reinforcement product types. The paper also explores how the tensile strength values of a product can vary depending on the population of tests used to compute strength values. The differences in choice of nominal tensile strength based on lot-specific and minimum average roll value (MARV) are discussed. The paper demonstrates that the Simplified Stiffness Method soil failure limit state will usually control the selection of the reinforcement and not the tensile strength limit state. While the primary motivation for this study is to find creep stiffness values for the Simplified Stiffness Method, the stiffness-strength equations are useful in other applications such as numerical modelling of geosynthetic-reinforced structures where a reinforcement stiffness value corresponding to post-construction low tensile strain conditions is required.

Optimum design of reinforced earth walls using evolutionary optimization algorithms

This study addresses the optimum cost design of mechanically stabilized earth (MSE) using geosynthetics. The design process of MSEs is mathematically programmed based on an objective function depending on the length of reinforcements and vertical distance of reinforced layers. Design restrictions control the final design to be valid in terms of constraints. The aim is to explore the efficiency of evolutionary-based algorithms in dealing with MSE optimization problem along with automating the minimum cost design of MSE walls. To this end, three evolutionary algorithms, differential evolution (DE), evolution strategy, and biogeography-based optimization algorithm (BBO), are tackled to solve this problem. Comprehensive computational simulations confirm the impact of different effective parameters variation on the final design. Finally, the BBO algorithm performed the best, while DE recorded the most unsatisfactory results.

Closure to “Assessment of Reinforcement Strains in Very Tall Mechanically Stabilized Earth Walls” by Armin W. Stuedlein, Tony M. Allen, Robert D. Holtz, and Barry R. Christopher

In the course of analyzing data collected from two exceptionally tall mechanically stabilized earth (MSE) walls constructed for the third runway at Seattle-Tacoma International Airport (SeaTac), the authors failed to understand three fundamental points regarding MSE wall design: 1. The authors ignore both the mandated design friction angle and the fact that the actual backfill internal friction angle was not known when the wall was designed. Instead, they assess the accuracy of the MSE design methods using selected in-place values of the soil friction angle, 40 and 44 , which are substantially higher than the mandated design friction angle, 37 . 2. The authors also ignore the fact that MSE walls are designed for the finished condition, not for the partially constructed condition. Instead, they condemn the validity of the Coherent Gravity and Simplified design methods based on those methods’ underprediction of reinforcement loads at intermediate stages of construction. Postconstruction stresses in the soil reinforcements at SeaTac are consistent with those predicted by the Coherent Gravity and Simplified methods using the mandated design friction angle, 37 . 3. The earth pressure distribution behind an MSE wall is triangular, not trapezoidal as assumed by the K-Stiffness method.

Load and Resistance Factors for External Stability Checks of Mechanically Stabilized Earth Walls

The use of load and resistance factor design (LRFD) to design geotechnical components of transportation infrastructure in the United States is now mandated by the Federal Highway Administration (FHWA). The advantages of LRFD over working stress design (WSD) may lead to its gradual adoption in geotechnical design even in the absence of any mandates. If load and resistance factors are based on reliability analysis, a mechanically stabilized earth (MSE) wall may be designed to a target reliability index (or a target probability of failure). Load and resistance factor design of MSE walls must consider multiple ultimate limit states, associated with both external and internal stabilities. This paper develops factors for use for the two ultimate limit states, sliding and overturning, used in design that are related to the external stability of MSE walls. Equations that closely reproduce the ultimate limit states with as little uncertainty as possible are proposed. The uncertainties of the parameters and the transformations for ultimate limit state equations are assessed using data from an extensive literature review. The first-order reliability method (FORM) is then used to produce resistance factor values for each limit state for different levels of target reliability index.

Practical analysis and design of mechanically-stabilized earth walls—I. Design philosophies and procedures

Design methods with the important design/construction considerations for mechanically-stabilized earth (MSE) walls are described. A general analysis/design procedure for MSE wall systems is discussed in detail. The effects of design methods, particularly the impact of the new load and resistance factor design (LRFD) method, on MSE walls are discussed in the companion paper (Part II) through the use of realistic examples. To ease the comparisons among the various design approaches, a unified notation is used to express all equations.

Practical analysis and design methods of mechanically-stabilized earth walls—II. Design comparisons and impact of LRFD method

A number of realistic mechanically-stabilized earth (MSE) wall systems are investigated using the general analysis/design procedure described in the companion paper (Part I). Comparisons among the various design methods are made. Impact of the new Load and Resistance Factor Design (LRFD) method on MSE wall design is discussed. To ease the comparisons among the various design approaches, a unified notation is used to express all design parameters.