Mechanically Stabilized Earth Research Articles

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.

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.

Estimation of confidence in the calculated resistance factor for simple limit states with limited data for load and resistance model bias

Estimation of the resistance factor in load and resistance factor design (LRFD) calibration for simple soil-structure limit states is most often based on model bias data of limited size. Frequently, the bias data are only available or required for the resistance term. In this paper, the confidence in the estimate of the mean of the resistance factor is computed for the case of one resistance factor and one load factor where limited model bias data are available for both load and resistance terms. The bootstrap method is used to compute synthetic load and resistance bias data sets from which confidence intervals on the point (mean) estimate of the resistance factor and load factor are computed. A closed-form solution is used to calculate the resistance factor for a single prescribed load factor and target reliability index, bias data, and nominal load and resistance variables that are lognormally distributed. However, the approach is general using Monte Carlo simulation. The method is demonstrated using the case of the internal stability pullout limit state for steel strip mechanically stabilized earth (MSE) walls. The example demonstrates the quantitative influence on pullout design using upper and lower 95% confidence interval limits for load and resistance factors.

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.

Large-Scale Hydraulic Performance Testing of a Geotextile Mechanically Stabilized Earth (MSE) Wall Constructed with Recycled Concrete Aggregate Backfill

Abstract Constructing geosynthetic mechanically stabilized earth walls with recycled backfill materials reduces environmental impacts and financial cost compared with their gravity wall counterparts. While a large database of column-scale tests to evaluate the hydraulic performance of recycled backfill materials exists in the literature, clogging potential under multidimensional flow conditions has not been examined. A large-scale reinforced soil wall and a complementary column test constructed with recycled concrete aggregate (RCA) and closely-spaced woven geotextile reinforcement were tested to examine chemical and physical clogging under wetting-drying cycles. Internal moisture migration and the evolving chemical signature of leachate were measured. Geotextile samples were exhumed after the tests and analyzed to evaluate chemical (tufa formation) and physical (fines migration) clogging. The complementary multidimensional and column experiments afford direct comparison of outflow chemistry and effects on geotextile permittivity. Geotextiles in the large-scale wall and column tests did not show any evidence of chemical or physical clogging and no evidence of positive pore pressures was detected. Outflow leachate from the wall test had higher total dissolved solids values and higher concentrations of Ca and SO4 in comparison to the column test. The pH of leachate from the column test is initially lower than from the wall, but results become similar (pH ∼12) at test completion. Leachate from both tests is supersaturated with tufa minerals. Differences in leachate characteristics of the two tests can be attributed to the initial moisture content of the backfill, larger quantity of RCA material in the large-scale wall, and the multidimensional flow characteristics of the large-scale wall. Results validate previous observations from column tests in terms of moisture retention and chemical response when flow conditions are multidimensional. Maintaining a free-draining backfill under conditions that could promote clogging (closely-spaced woven geotextile reinforcement layers) gives further confidence in using RCA as backfill under these conditions.

Evaluation of Construction and Demolition Waste and Other Alternative Fills for Strip-Reinforced Soil Walls

This article assesses the pullout performance of ribbed metallic strips embedded in fill soils that do not conform to conventional design criteria for mechanically stabilized earth (MSE) walls. These alternative fill soils include gravelly and sandy recycled aggregates from construction and demolition waste, artificial and natural sands, and fine-grained lateritic soil. The research included soil characterization tests and large-scale pullout tests, conducted as part of this study. The results showed that the reinforcement pullout behavior was similar for recycled, artificial, and natural sands, indicating that soil particle size played a crucial role in mobilizing the interface pullout resistance. However, in the case of recycled sand, stress concentration at the reinforcement level led to particle crushing during pullout conditions, causing this material to exhibit less efficient performance compared to other sands. The fine-grained lateritic soil demonstrated inferior behavior compared to sandy soils, despite the interparticle bonding provided by the sesquioxide coating characteristic of intensely weathered tropical soils. Finally, an analytical prediction tool based on experimental results was developed, providing an alternative method to make conjectures about the performance of different soils during the pre-design stages, particularly based on particle size attributes.

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.

Case Study of Mechanically Stabilized Earth (MSE) Retaining Wall Failure in the State of Tennessee; Recommendations for Future Design and Constructions

This study presents an investigation into the failure of a Mechanically Stabilized Earth (MSE) retaining wall in Tennessee, USA. The wall was constructed to support an embankment development, but it failed catastrophically, causing damage to the road and posing a significant safety risk to the public. The investigation involved a comprehensive site visit, field data collection, laboratory testing, and numerical modeling. Our investigation revealed that the failure of the retaining wall was caused by inadequate construction practices. Specifically, the wall was not constructed in accordance with design specifications, and the backfill material used was not properly compacted. The construction issues resulted in the differential settlement of the wall, which ultimately caused it to fail. Based on our findings, we propose a set of recommendations for the design and construction of future retaining walls in similar geotechnical conditions. The recommendations include the proper selection and use of backfill material, proper compaction of backfill, and adherence to design specifications. The results of this study are expected to contribute to the development of improved design standards and construction practices for MSE retaining walls in Tennessee and other regions with similar geotechnical conditions.

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.

The role of geosynthetic stiffness in soil reinforcement applications

Most often the focus on the mechanical contribution of reinforcement geosynthetics in soil reinforcement applications has been on the strength of the material. In fact, under operational conditions the performance of these systems is controlled by the stiffness of the geosynthetic, not its strength. An appreciation of the role of geosynthetic stiffness in soil reinforcement applications is complicated by the rate-dependency of many products which means that their load-strain properties are time-, strain- and temperature-dependent. This paper describes the quantification of these properties using a simple isochronous load-strain model with properties fitted from laboratory creep testing. The implementation of the model and its consequences on the quantitative performance of mechanically stabilized earth (MSE) wall loads and deformations, reinforced fills over voids, and a thin reinforced granular base over a soft clay foundation are demonstrated.

Experience from design & construction of a stable feature MSE wall in Dubai

There has been continued development of various methods for mechanically stabilized earth (MSE) wall construction, often by specialized system providers, to solve problems when the available width of reinforced fill is highly restricted. The design manual FHWA-NHI-10-024 permits to reduce the length of soil reinforcements up to 30% of wall height in shored or stable featured walls. There are many instances where the available width is much less than the limits by design standards, necessitating innovative approaches. The current project involves constructing a link road as a diversion at the middle of an existing 6m high ramp made of concrete wall. The new ramp will be retained by MSE wall that will be joined to the old concrete wall within tight space limitations. To accomplish this 'stable feature MSE wall' within narrow space, it was imperative to adopt a novel method of actively connecting geogrid reinforcements and modular block fascia to existing concrete wall. This paper presents the challenges in designing a stable feature MSE wall in extremely narrow space. The presented approach of connecting the soil reinforcement to the concrete anchors was a determining factor in the project and could therefore be adopted for future projects under similar conditions.

Effect of a two-tiered configuration on the seismic behaviour of reinforced soil walls

Shaking table tests were performed on reduced-scale models of integrated and two-tiered mechanically stabilised earth (MSE) walls to evaluate the effect of a tiered configuration on the seismic behaviour of metal-strip and geogrid reinforced soil walls. The results showed that, although inextensible reinforcements could reduce the fundamental period, acceleration amplification and lateral deflection and improve wall stability, these benefits declined with the use of a tiered configuration and gradually faded with an increase in the offset distance. This made changing the degree of extensibility a low-impact factor in two-tiered MSE walls with a sufficiently large offset distance (D > (0.4–0.5)H). In order to benefit from the advantage of a tiered configuration, it was found that 0.22H should be considered as the minimum offset distance. The findings indicated that preventing the development of a slip surface in the lower half of the wall, improving the seismic stability by increasing the failure threshold acceleration, mitigating acceleration amplification and decreasing the reinforcement load were the main advantages of a tiered configuration. Moreover, it was concluded that the Mononobe–Okabe method could be used to find the upper bound for estimating the reinforcement forces in two-tiered MSE walls.

Influence of reinforcement design on seismic stability of full-height panel MSE walls

A numerical study was carried out to investigate the seismic stability of mechanically stabilized earth (MSE) walls using a finite element limit analysis (FELA) approach. The numerical method was validated using results from shaking table tests and limit equilibrium (LE) analysis. A series of parametric analyses was subsequently carried out to examine the influences of reinforcement design on seismic stability and failure mechanisms in full-height panel MSE walls. Results of the study indicate that, as opposed to the linear or bilinear failure mechanisms typically assumed in current design guidelines, more complex failure geometries could form in the backfills that involve extended reinforcement, which can be captured and analyzed using the FELA method employed in this study. The results also confirm the current consensus that placing longer reinforcement layers at the top of the wall (i.e. tapering-down arrangement) can help improve its seismic stability. However, in shorter walls or when high-strength reinforcement is used, a tapering-up reinforcement arrangement could also lead to increased seismic stability.