Mechanically Stabilized Earth Walls Research Articles

Environmental impacts of mechanically stabilised earth walls

Mechanically stabilised earth (MSE) walls have gained widespread popularity in North America because of their cost-effectiveness and reliable performance. Although the use of carbon-intensive materials for MSE walls is significantly lower compared to conventional retaining walls like concrete gravity walls and cantilever walls, heavy earthwork and transportation activities are involved in the construction of MSE walls, which increase their carbon footprint. The intensity of construction and transportation activities need particular attention because these are heavily reliant on the combustion of fossil fuels. In this study, the environmental impacts of MSE walls, reinforced by two common types – steel strips and geogrid – are quantified using life cycle assessment (LCA). A parametric study is conducted to investigate the effects of (i) soil properties, (ii) material properties of reinforcement, (iii) applied load, (iv) design parameters, and (v) hauling distances of materials on the global warming impact of MSE walls. Based on the study, reference charts are developed for the purpose of quick estimation of global warming impact of MSE walls based on design dimensions, applied load, and site conditions.

Seismic Safety Evaluation of Mechanically Stabilized Earth (MSE) Wall for Highway Construction

The usage of Mechanically Stabilized Earth (MSE) Walls has grown in popularity over the last few decades and has been widely used in many countries for highway construction, including Indonesia. As a country with a high risk against seismic hazards, a considerable stability analysis against earthquakes for construction must be conducted. This paper is directed to evaluate the static and seismic stability of MSE wall by adopting design criteria from SNI 8460:2017 using the pseudo-static approach with Limit Equilibrium Method (LEM) which modelling earthquake as a seismic coefficient, a one-way constant load and dynamic response approach with Finite Element Method (FEM) which modelling earthquake as ground motion, a fluctuating load which varies in time. The stability analysis is performed by considering three failure mechanisms that mostly occurred in MSE Walls; base sliding, tensile overstress, and slope failure. The earthquake load is modelled based 1000-year return period earthquake. Based on the analysis result, the most potential failure mechanism that may occur in the MSE wall is tensile overstress, while the least potential failure is base sliding. The analysis result also shows that the finite element method obtained higher safety factors compared to limit equilibrium, while on the other hand, the remaining two failure mechanisms shows the different result, with the finite element method obtaining lower safety factors than limit equilibrium. Modelling seismic load as an accelerogram indicates that earthquakes have higher impacts on structure stability compared to seismic coefficient, based on seismic safety factor reduction of each method. Although show differences in the value of the safety factor, the minimum safety factor required still complies with both methods.

Geosynthetic MSE walls research and practice: past, present, and future (2023 IGS Bathurst Lecture)

The technology of geosynthetic mechanically stabilized earth (MSE) walls can help solve classical geotechnical earth retaining wall problems. It can also contribute to achieving the new required performance for infrastructures, such as reliance and sustainability. To further develop this technology, it is essential to analyze the history of its progress. This study summarizes the state-of-the-art research on the mechanical and soil interaction properties of geosynthetics, physical modeling and in situ measurements, analytical and numerical modeling, and reliability analyses by reviewing approximately 728 papers published in well-known international journals in this field and some notable conference paper contributions during the period of approximately 50 years from 1972 to 2023. The latest analytical methods, such as risk-based life cycle cost and CO2 emission assessments and damage/failure predictions, are introduced to evaluate the resilience and sustainability performance of geosynthetic MSE walls. Finally, the prospects of a seismic isolation technique with new types of geosynthetics and life cycle management using a long-term sensor for geosynthetic MSE walls are discussed.

Applicability of Digital Image Photogrammetry to Rapid Displacement Measurements of Structures in Restricted-Access and Controlled Areas: Case Study in Korea

Critical facilities are generally located in areas with restricted or controlled access, making it difficult for experts to monitor the structural health of enclosed infrastructures. Hence, a case study was conducted in South Korea to evaluate the applicability of digital image photogrammetry using commercial imaging devices in order to quickly measure the structural deformations of infrastructures in such areas. The applicability evaluation involved measuring the displacement of mechanically stabilized earth (MSE) walls. In the experiment, the displacement of MSE walls was first measured using the traditional monitoring method and the results were compared with those obtained via digital image photogrammetry using commercial imaging devices such as digital cameras and cellphones. The measurement results obtained with the cellphone camera had a maximum error of approximately 20 mm when compared with the results of the traditional monitoring method. Because this is a significant error, even when considering the mechanical error in the traditional monitoring method’s result, it was determined that monitoring using a cellphone camera is infeasible. However, the experimental results of digital image photogrammetry using a digital camera showed a maximum error of approximately 9 mm. Although this is a sizable error, the method was assessed to be technically feasible.

Numerical analysis of shored mechanically stabilized earth walls

ABSTRACT This study investigates the deformation and stability of shored mechanically stabilized earth (SMSE) walls using numerical analysis. A finite element (FE) model is developed in Plaxis, and parametric sensitivity analysis is conducted to identify the most influential input parameters on the maximum lateral facing displacements of the mechanically stabilized earth (MSE) and soil nail (SN) walls and global factor of safety (FS) of the SMSE wall. Predictive equations are developed for these responses using multiple linear regression. The suitability and adequacy of the developed predictive equations are assessed by evaluating the summary of fit statistics. It is observed that the governing failure mechanism of the SMSE wall is a bilinear failure plane. Its inclination angle is 10° less than that of the Rankine failure surface. The external stability of the SMSE wall is more critical compared to the conventional MSE wall. It is concluded that special attention should be given to the interfaces and connections due to the vulnerability to reinforcement-facing connection failure.

Numerical investigation on the behaviour of Post-Tensioned Mechanically Stabilised Earth Walls (PT-MSEW)

This study reports on a numerical investigation on the behaviour of an innovative retaining wall system named Post Tensioned Mechanically Stabilised Earth Wall (PTMSEW). In the proposed system, Post-Tensioning (PT) technique was integrated into the common retaining wall and the Mechanically Stabilised Earth Wall (MSEW) construction method to improve the performance of MSEWs and limit their failure modes. The variables of this study were wall height, PT force, pre-cast segment size, surcharge load, foundation size, and soil reinforcement length. The study found that incorporating PT stress into the MSEW improved the performance of the retaining wall by decreasing horizontal displacement of the wall face, soil reinforcement tensile forces, and backfill settlements and significantly enhanced the passive resistance of the wall. The introduction of a small amount of PT force prevented local failures caused by the relative movement of face segments. It was observed that by applying only a small level of post-tensioning, the lateral load-carrying capacity and passive resistance of the proposed PT-MSEW system can be significantly improved over that of its conventional counterpart. This opens new possibilities for the use of MSEW in the construction of taller retaining walls.

A Bibliometric Review of Reinforced Soil Wall Research Topics

Reinforced soil or mechanically stabilized earth (MSE) wall structures offer straightforward construction techniques as an alternative to conventional retaining earth walls. The benefits of MSE wall structures are their low cost, rapid construction, minimal ground occupation, and high tolerance for differential settlements. In the past, a vast amount of research has been conducted on this specific topic, but there is no state-of-the-art overview on the general reinforced soil walls subject. In this paper, a bibliometric review of MSE walls literature is carried out to provide multiple data points regarding the state-of-the-art in MSE wall publications. To present/demonstrate the main traditional applications, current utility, and last developments of MSE walls, a thematic/keyword cluster categorization is performed to catalog and organize the numerous applications analyzed and published in the last 4 decades. Furthermore, a discussion of MSE wall characteristics is conducted to assist researchers in expanding their understanding of potential future research areas.

Environmental sustainability and life cycle assessment of pilot scale application of coal combustion residue as structural fill in mechanically stabilized earth walls

In this study, three types of coal combustion residue (CCR) have been used, and the life cycle impact of CCR as structural fill behind mechanically stabilized earth (MSE) walls of three different heights has been conducted. The analysis has been done using OpenLCA software. Results have been compared with MSE walls using natural sand as a structural fill. It is observed that the environmental impacts of using CCR reduce by more than 50 % compared to those of using natural sand. Amongst CCR, the maximum impact is shown by fly ash and the least by bottom ash. Relative to natural sand, the impacts of using CCR decrease with an increase in wall height. The cost analysis of the walls indicates that if structural fills are transported from the same distance, the cost of construction with natural sand is 18–46 % higher than that by CCR as fill. Results reveal that utilizing CCR as structural fill in MSE walls proves to be a more economic and eco-conscious choice compared to the conventional natural soil. These findings could hold considerable implications for the construction sector and its efforts to minimize ecological footprint.

Case Study on Instrumenting and Monitoring Geosynthetic-Reinforced Pile-Supported Mechanically Stabilized Earth Wall Built over Soft Soil

This paper presents a case study on instrumenting, monitoring, and finite element modeling (FEM) of geosynthetic-reinforced pile-supported (GRPS) mechanically stabilized earth (MSE) walls. The GRPS-MSE wall was monitored using various instruments such as piezometers, earth pressure cells, shape-acceleration arrays (SAAs), and strain gauges. The performance criteria included efficacy, stress concentration ratio (SCR), differential settlement, and reinforcement tension. Collected data, such as excess pore-water pressures, contact pressures on pile and soft soil, differential settlements, and lateral displacement of MSE wall, were analyzed thoroughly. A 3D FEM was also developed to simulate the GRPS MSE wall, and the results are in good agreement with field data. The results demonstrated significant load transfer from soil to piles as a result of soil arching, yielding 30–32 SCR. The field efficacy was measured at 37.69 %, while the FEM efficacy was estimated as 42.4. Strains in geogrids within the geosynthetic-reinforced load transfer platform (GLTP) system were under 1%, less than the 5% maximum recommended by FHWA. The maximum differential settlement measured between pile cap and soft soil from SAAs is 7.1 mm, while it is estimated to be 8.3 mm from FEM. The MSE wall exhibited low lateral displacement (<25 mm), indicating enhanced stability because of GLTP. The comparison between five analytical GLTP design methods showed that the CUR226 methods gave the closest results to field measurements and FEM results. This study offers crucial insights into leveraging GLTP and MSE walls in highway construction.

Physical and Numerical Models of Mechanically Stabilized Earth Walls Using Self-Fabricated Steel Reinforcement Grids Applied to Cohesive Soil in Vietnam

Mechanically stabilized earth (MSE) walls have been widely applied in construction to maintain the stability of high embankments. In Vietnam, imported reinforcement materials are expensive; thus, finding locally available materials for MSE walls is beneficial. This study examines the behavior of an MSE wall using local reinforcement materials in Danang, Vietnam. The MSE was reinforced by self-fabricated galvanized steel grids using CB300V steel with 3 cm ribs. The backfill soil was sandy clay soil from the local area with a low cohesion. A full-scale model with full instrumentation was installed to investigate the distribution of tensile forces along the reinforcement layers. The highest load that caused the wall to collapse due to internal instability (reinforcement rupture) was 302 kN/m2, which is 15 times greater than the design load of 20 kN/m2. The failure surface within the reinforced soil had a parabolic sliding shape that was similar to the theoretical studies. At the failure load level, the maximum lateral displacement at the top of the wall facing was small (3.9 mm), significantly lower than the allowable displacement for a retaining wall. Furthermore, a numerical model using FLAC software 7.0 was applied to simulate the performance of the MSE wall. The modeling results were in good agreement with the physical model. Thus, self-fabricated galvanized steel grids could confidently be used in combination with the local backfill soil for MSE walls.

3D numerical analysis of corner mechanically stabilized earth walls

ABSTRACT MSEW (Mechanically Stabilized Earth walls) has become a widely adopted and economical earth-retaining system. However, the current design standards primarily rely on a two-dimensional plane-strain approach, overlooking the critical 3D behavior and mechanisms associated with wall curves and corners. To address this gap, this research aims to enhance our comprehension of MSEW corner performance for right-angle (Sharp turns) and curved (Round off) walls by using 3D finite element modeling. A comparative study was conducted for MSEW in case of sharp turns and round off walls, in addition to examining the influence of the curve angle in the different cases with angles (internal curve angle) of 50 to 120 degrees. Based on results of comparing the right-angle wall and the curved angle (90º) wall, it is evident that the horizontal displacement of the right-angle wall is greater. For curved wall, it was observed that the value of horizontal displacement is minimal at the beginning of the curved wall and gradually increases until it reaches the maximum displacement at the mid of the curve in plan view. The geogrid strain for the right-angle wall is approximately 1.70 times of the curved wall (internal curved angle = 90°). Based on the results of difference angle of curved wall, it was concluded that the horizontal displacement values of the wall between internal curved angles 90 and 120 are quite close, but they differ significantly from 50 to 90. It was noted that, the maximum displacements for angles from 60 and 110 was occurred at approximately 0.38 H of the wall’s height from the base but, it equal to 0.50 H for angle 110 and 120. Finally, an equation of second degree can be deduced to illustrate the relationship between the maximum facing wall displacement and the wall height with the curved wall angle.

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.

Seismic Response Compression of Various MSE Walls Based on 3D Modeling

This study evaluates the earthquake-induced movement of mechanically stabilized earth (MSE) walls. A thorough investigation was conducted on an MSE wall model, utilizing a comprehensive finite element (FE) analysis. This research focuses on investigating and designing MSE walls made of reinforcement concrete and hollow precast concrete panels. It also involves comparative studies such as on the vertical pressure of the wall, horizontal pressure of the wall, lateral pressure of the wall, settlement of the wall, settlement of the backfill reinforcement, vertical pressure of the backfill, horizontal pressure of the backfill, lateral pressure of the backfill, vertical settlement of the foundation, and settlements of soil layers across the height of the MSE walls. The FE simulations used a three-dimensional (3D) nonlinear dynamic FE model of full-scale MSE walls. The seismic performance of MSE walls has also been examined in terms of wall height. It was found that the seismic motion significantly impacts the height of the walls. In addition, the validity of the proposed study model was assessed by comparing it to the reinforcement concrete wall and ASSHTO guidelines using finite element (FE) simulation results. Based on the findings, the hollow prefabricated MSE wall was the most practical alternative due to its lower displacement and settlement. The specifics of the modeling approach used in this study and the lessons learned serve as benchmarks for future comparable lines of inquiry and practitioners, especially as the computational power of desktop computers continues to rise.

Determination of shear stress-shear strain behavior of polymeric geostrip reinforced MSE wall

In this paper, the shear strain-dependent dynamic response properties of a retaining wall model made of mechanically stabilized earth (MSE) with polymeric geostrip material are investigated in a 1-g shaking table test. The values of lateral displacements and accelerations measured at different points along the MSE wall surface were used to evaluate the equivalent hysteris loops. The effect of reinforcement stiffness and backfill slope angle on the equivalent shear stiffness modulus (Ge) and damping ratio (D) were investigated. The experimental results show that the variation of shear stiffness modulus and damping ratio as a function of shear strain (γ) is affected by vertical pressure (σv), but the effect of the stiffness of the polymeric geostrip on the damping ratio is negligible. The variations of the Ge, Ge/σv, Ge/Gmax, and D as a function of γ are expressed in exponential equations with high least squares values in this study.

A Case Study on Distresses of Concrete Pavements Supported on a Retaining Wall

Embankments and retaining walls are integral parts of the bridge system and provide a smooth transition from lower elevations (i.e., roadways) to higher elevations (i.e., bridge decks). Performances of pavement structures supported on embankments or retaining walls are directly related to their conditions. This paper presents a comprehensive case study of the evaluation of pavement structures supported on an in-service mechanically stabilized earth (MSE) wall that showed significant distresses, such as lane separation, faulting, lane settlement, and tilting of the MSE wall. The conditions of the pavement structures were evaluated via visual observations, falling weight deflectometer (FWD) tests, and coring through pavement structures. The conditions of the MSE wall were evaluated through dynamic cone penetrometer (DCP) tests, cone penetration tests (CPTs), LiDAR surveys, and soil borings. Detailed analysis of the data obtained in this study provides valuable insights into potential distress mechanisms.

Failure Mechanism and Deformation-Based Design of Narrow Geosynthetic Reinforced Soil Walls

In recent years, the working performance of mechanically stabilized earth (MSE) walls has shown their outstanding stability and capacity to accommodate large deformation. The behavior and failure mechanisms of conventional MSE walls have been carefully examined. In cases where space is limited, such as in mountainous regions, in coastal regions, and for road expansion, the conventional MSE wall can be modified by adjusting the length of reinforcement to conform the construction area. For narrow geosynthetic reinforced soil (GRS) wall, the modification and arrangement of reinforcement components, including reinforcement tensile strength, vertical spacing, and aspect ratio, play key roles in the behavior of reinforced earth walls and can also lead to differences in the distribution of lateral earth pressure compared with conventional MSE walls. In this study, a series of geotechnical centrifuge tests are conducted to clarify the failure behaviors, distribution of lateral earth pressure, and deformation progresses of narrow GRS walls. Among the investigated variants, it is verified that improved reinforcement strength leads to a significant decrease in horizontal wall displacement. The relationship among lateral earth pressure, zero-earth-pressure zone, and horizontal displacement can be applied to predict the deformation of a narrow GRS wall.

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.

Pullout Behavior of a Polymeric Strap in Compacted Dry Granular Material

Strap reinforcement is very commonly used as reinforcement material in mechanically stabilized earth walls (MSEW). Metal straps are mostly used as reinforcement material. However, in humid climates, where the risk of damage to metal straps due to corrosion is high, the use of geosynthetic straps is quite justified. In the Croatian coastal region, geosynthetic straps were used as reinforcement for two very high MSEWs. In both cases, the backfill material crushed stone aggregate from the neighboring site was used. According to the relevant standards, it is recommended that the backfill material should have a uniformity coefficient of Cu ≥ 4.0. To meet these requirements, it is usually necessary to sieve and crush the backfill material. To evaluate the influence of the uniformity coefficient on the friction interaction coefficient between a geosynthetic strap and a crushed stone aggregate, a series of pullout tests with different confining stresses and aggregate grain size distributions were conducted. The pullout tests were performed for three different uniformity coefficients of the crushed stone aggregate. The results confirmed the justification to use backfill material with a uniformity coefficient higher than 4.0. The pullout tests were performed with one strap, two closely spaced straps, and two separated straps. The results showed that lateral friction contributes to the pullout force in the amount of 16.1% of the total force.

Seismic performance of mechanically stabilized earth walls with Sand-Crumb rubber backfills of varying proportion

The applicability of crumb rubber mixed with sand as alternative fill material in mechanically stabilized earth (MSE) walls is investigated in the current study. Shaking table tests have been conducted to analyze the dynamic response of model geogrid reinforced earth walls subjected to three different base input motions. Eight different sand-crumb rubber mixture combinations were used as backfill. The outcomes of this study provide quantitative results on how base excitation amplitudes could influence the seismic behavior of the MSE walls in the presence of sand-rubber backfill. The results have been analyzed in terms of deformation and rotation of the wall, settlement of backfill, acceleration amplification, and earth pressure response. Wall displacement and backfill settlement was found to reduce with the addition of rubber in the sand. The maximum displacement at the top of the wall was found to reduce by 45% at a rubber content of 30% for high peak ground acceleration (PGA) input motion. Two-wedge failure was observed with the failure envelope inclined at an angle of 49° from the vertical. Apart from this, the strain in the geogrid was decreased with an increase in the rubber content. Hence, the rubber content of 30% mixed with sand can be considered an optimum percentage to control the dynamic performance of MSE walls. In the end, a cost-benefit analysis was conducted, and it was found that using rubber as a partial substitute for sand backfill reduces the overall cost of the project. This research will also promote the use of recyclable rubber as a construction material in highway construction.