Rigid Facing Research Articles

Full-scale mechanically stabilized earth (MSE) walls under strip footing load

This study analyses two full-scale model tests on mechanically stabilized earth (MSE) walls. One test was conducted with a rigid and one with a flexible wall face. Other parameters were the same in these two tests, like the number and type of geogrid layers, the vertical distance between the layers and the soil type. The loads and strains on the reinforcement are measured as function of the horizontal and vertical earth pressure and compared with analytical models. Specifics regarding the behavior of the geogrids under the compaction load during the construction of the model and under strip footing load are included in the study. Results are compared with AASHTO and the empirical K-stiffness method. In this study, an analytical method is developed for the MSE walls taking into account the facing panel rigidity both after backfill construction and after strip footing load. There is good agreement between the proposed analytical method and the experimental results considering the facing panel rigidity. The results indicate that the tensile force on reinforcement layers for rigid facing is less than the flexible facing. The maximum strains in the reinforcement layers occurred in the upper layers right below the strip footing load. The maximum wall deflection for the flexible facing is more than for the rigid facing. The maximum deflection was at the top of the wall for the rigid facing and occurred at z/H = 0.81 from top of the wall for the flexible facing.

Analytical method for calculating natural frequencies of geosynthetic-reinforced wall with full-height concrete facing

Based on the theory of beams on elastic foundations, a new analytical solution for calculating the natural frequencies of reinforced-soil retaining walls is presented. The assumed retaining wall is geosynthetic-reinforced, with a full-height rigid concrete facing (a GRS-FHR wall). The current study takes into account the rigid body motion of these walls for the first time, and two analytical formulae for calculating the natural frequencies of the rigid mode of deformation for reinforced retaining walls are presented through an exact solution. Next, applying the energy method, a new analytical formula for calculating the natural frequency of the flexural deformation mode is developed. Another innovation is the modeling of the foundation soil with both rotational and translational springs, which makes it possible to consider rocking and sliding deformation modes for retaining wall motion. Moreover, the effect of backfill soil interaction is taken into consideration by translational springs along the wall. The results thus obtained are then compared with numerical analysis using Ansys software, and an excellent agreement was observed.

Design and construction of the first GRS integrated bridge with FHR facings in Europe

Abstract The bridge across the Pavlovski potok stream in the village of Žerovinci in northeast Slovenia is a part of the investment into the modernisation of the Pragersko–Hodos railway line, one of the biggest investments in the infrastructure in Slovenia at the moment. Its design was accompanied by very short deadlines and a deep layer of soft foundation soil. For this reason the reinforced concrete abutments of a nearby railway bridge were founded on 24 m deep piled foundations. Short deadlines and a limited budget forced the authors of this paper to find an alternative solution. Deep piled foundations were replaced by shallow foundations made of compacted fill material reinforced with geosynthetics. The bridge was completed by the end of 2014. From the results of previous laboratory tests that were obtained within the scope of the EU co-funded research project “Research voucher”, the basic characteristics of the building materials for the geosynthetic reinforced soil (GRS) bridge abutments, as well as the deformation properties of the typical reinforced soil were obtained. These data were used for the design of the abutments. The staged construction procedure of full height rigid (FHR) facings for the GRS retaining walls (RW) was used for the construction of this GRS integrated bridge. Partial pre-stressing of geogrids and consequently the increased stiffness of the reinforced soil was achieved by following the staged construction procedure. The bridge system consisted of a cast-in-situ RC slab, which was placed on top of the GRS immediately behind the FHR facings, i.e. the bridge was constructed as a simply-supported slab supported by a pair of GRS abutments, without the use of bearings. Thus the described bridge across the Pavlovski potok combines two approaches for GRS integrated bridge design, one of which has been used in Japan (Tatsuoka et al., 2009), with full structural integration of the deck onto the pair of FHR facings, other being proposed by the FHWA (Adams et al., 2010), without full integration of the deck onto the GRS RWs. A system for the monitoring of structure performance was established in order to ensure optimization of this kind of structure. Data for this GRS integrated bridge, which were obtained during the construction works were compared to similar data obtained from the construction of a nearby railway bridge with reinforced concrete abutments. The comparison provides a good basis for future decisions when choosing the type of bridge abutments.

2E12 Design and construction of geosynthetic-reinforced soil structures for Hokkaido Shinkansen(Infrastructure)

The southern part between Shin-Aomori Station (at the north end of Main Island) and Shin-Hakodatehokuto Station (at the south end of Hokkaido Island) of a new high-speed train line called Hokkaido Shinkansen was nearly completed by the end of 2014 and will be opened in 2016. In a range of 37.3 km at the south end of Hokkaido Island, a number of various types of geosynthetic-reinforced soil (GRS) structure were constructed: i.e., 1) GRS retaining walls (RWs) having full-height rigid facing for a length of about 3.5 km, having fully replaced the conventional type RWs; 2) in total 29 GRS bridge abutments, having fully replaced the conventional type bridge abutments; 3) a GRS integral bridge, the world-first one at Kikonai; 4) three GRS box culvert structures integrated to adjacent GRS RWs; and 5) nine GRS protection structures at the tunnel entrance. These GRS structures have been constructed most densely ever for railways, which is definitely so for high speed trains. This paper describes the design and construction of these GRS structures with several lessons learned from this project are summarized.

Design and construction of geosynthetic-reinforced soil structures for Hokkaido high-speed train line

The southern part between Shin-Aomori Station (at the north end of Main Island) and Shin-Hakodate Station (at the south end of Hokkaido Island) of a new high-speed train line called Hokkaido Shinkansen is nearly completed as of the end of 2013 and will be opened in 2015. In a range of 37.3 km at the south end of Hokkaido Island, a number of various types of geosynthetic-reinforced soil (GRS) structure were constructed: i.e., (1) GRS retaining walls (RWs) having full-height rigid facing for a length of about 3.5 km, having fully replaced the conventional type RWs; (2) in total 29 GRS bridge abutments, having fully replaced the conventional type bridge abutments; (3) a GRS integral bridge, the world-first one at Kikonai; (4) three GRS box culvert structures integrated to adjacent GRS RWs; and (5) nine GRS protection structures at the tunnel entrance. These GRS structures are those that have been constructed most densely ever for railways, which is definitely so for high speed trains. In this paper, the design and construction of these GRS structures is described while several lessons learned from this project are summarized.

Geosynthetic-Reinforced Soil Structures for Railways in Japan

Geosynthetic-reinforced soil retaining walls (GRS RWs) have been constructed for a total length of about 150 km as of June 2013 mainly for railways, including high-speed train lines. After a full-height wrapped-around GRS wall has been constructed and the major residual deformation of the backfill and supporting ground has taken place, a full-height rigid (FHR) facing is constructed by casting-in-place concrete on wrapped-around wall face in such that it is firmly connected to the reinforcement layers. A number of this type GRS RWs performed very well during the 1995 Great Kobe and the 2011 Great East Japan Earthquakes. The seismic design code for railway soil structures has been revised taking into account such high-level seismic loads as experienced during the 1995 Kobe EQ. A number of conventional-type RWs and embankments collapsed during these and other earthquakes, heavy rains, floods, and storm wave actions. Many of them were reconstructed to this type GRS RWs and geosynthetic-reinforced embankments. Among a couple of new bridge types that have been developed, GRS integral bridge comprises a continuous girder of which both ends are structurally integrated without using bearings to the top of the facings of a pair of GRS RWs. The first prototype was constructed for a high-speed train line in 2011 and three more were constructed to restore bridges that fully collapsed by great tsunami during the 2011 Great East Japan EQ.

An analytical method for calculating the natural frequency of reinforced retaining walls with soil–structure interaction effect

ABSTRACT: Natural frequency is one of the most important parameters in the seismic behaviour of structures, including retaining walls. In this study the theory of beams on elastic foundations and the energy method were used to obtain a precise analytical formulation for the natural frequency of the fundamental mode of geosynthetic-reinforced soil-retaining walls. The assumed retaining wall was reinforced with full-height rigid concrete facing (GRS-FHR walls). Moreover, use of the suggested formula facilitates the consideration of soil and wall interaction in calculating natural frequency. The backfill and foundation soil of the retaining wall were modelled using translational springs. The result obtained from the suggested formula was compared with the result of numerical analysis using ANSYS software, and a good agreement was found.

A new analytical method for calculating seismic displacements in reinforced retaining walls

ABSTRACT: Calculating the seismic displacement of reinforced retaining walls is important for optimal design of these structures. Using the limit analysis theorem, in this study an innovative approach has been proposed for calculating the coefficient of yield acceleration and permanent displacements of geosynthetic-reinforced soil-retaining walls with full-height rigid concrete facing (GRS-FHR walls). In this manner, based on the upper-bound theory of limit analysis and Newmark's sliding block theory, a group of charts has been proposed to estimate the permanent sliding displacements and the coefficient of yield acceleration for this type of wall. In these charts, the effect of the following parameters on the magnitude of permanent displacements and on the coefficient of yield acceleration of the wall has been investigated: vertical spacing of reinforcements; ratio of width to height of facing; ratio of length of reinforcements to height of facing; and internal friction angle of the soil. Results obtained from the suggested method have been compared with the sliding displacements reported by other researchers as well as those measured at the toe of a well-known GRS-FHR wall called Tanata under the Kobe earthquake (Japan, 1995). The suggested charts are believed to provide an appropriate, handy tool for estimating the coefficient of yield acceleration and permanent sliding displacements of GRS-FHR retaining walls.

Comparison of numerical and analytical solutions for reinforced soil wall shaking table tests

The paper describes a simple numerical FLAC model that was developed to simulate the dynamic response of two instrumented reduced-scale model reinforced soil walls constructed on a 1-g shaking table. The models were 1 m high by 1.4 m wide by 2.4 m long and were constructed with a uniform size sand backfill, a polymeric geogrid reinforcement material with appropriately scaled stiffness, and a structural full-height rigid panel facing. The wall toe was constructed to simulate a perfectly hinged toe (i.e. toe allowed to rotate only) in one model and an idealized sliding toe (i.e. toe allowed to rotate and slide horizontally) in the other. Physical and numerical models were subjected to the same stepped amplitude sinusoidal base acceleration record. The material properties of the component materials (e.g. backfill and reinforcement) were determined from independent laboratory testing (reinforcement) and by back-fitting results of a numerical FLAC model for direct shear box testing to the corresponding physical test results. A simple elastic-plastic model with Mohr-Coulomb failure criterion for the sand was judged to give satisfactory agreement with measured wall results. The numerical results are also compared to closed-form solutions for reinforcement loads. In most cases predicted and closed-form solutions fall within the accuracy of measured loads based on ± 1 standard deviation applied to physical measurements. The paper summarizes important lessons learned and implications to the seismic design and performance of geosynthetic reinforced soil walls.

Progressive failure and shear band development within model-scale reinforced soil walls subject to seismic shaking

This paper discusses the results of an experimental study on model geosynthetic-reinforced soil (GRS) walls constructed with full-height rigid (FHR) facing. Ground accelerations, external deformations and localised strain fields were tracked, while stepped-amplitude sinusoidal seismic shaking events were applied via a shake table. The results of one of seven shake table tests are presented here, with a focus on the evolution of the pre-failure deformation of the wall at the end of the reinforced zone. This study shows that the deformation of ductile GRS walls with FHR facing subjected to seismic shaking is a progressive process of shear band development with depth as the wall rotates and, ultimately, translates towards failure.

Negative Pore Air Pressure Generation in Backfill of Retaining Walls During Earthquakes and its Effect on Seismic Earth Pressure

In order to investigate the seismic behavior of conventional type and geosynthetic-reinforced soil retaining walls, 1-g model shaking tests were conducted. Model walls having a height of about 50 cm were placed on a subsoil layer and backfilled with a layer of dense dry Toyoura sand. They were subjected to several steps of horizontal irregular excitations. As a result, generation of negative pore air pressure in the backfill was observed. The maximum amplitude of the negative pore air pressure during each shaking step increased with the base acceleration. Based on analyses of the measured data, it was inferred that such negative pore air pressure was caused by outward wall displacement relative to the backfill and not by dilative behavior of the backfill. It would cause a reduction in the seismic earth pressures exerted from the backfill. This feature suggests an advantage of a rigid full-height facing for reinforced soil walls over the segmental types of facing. A simplified numerical procedure to evaluate earth pressure was applied while considering the effects of the negative pore air pressure, and it could qualitatively simulate the measured behavior in terms of the seismic earth pressure and the angle of failure plane in the backfill.

An instrumented reinforced earth wall

Reinforced earth wall system has become very popular because of its aesthetic value and ease of construction. In order to optimize the design, it is important to understand its behavior during and after construction. This can be achieved either through field instrumentation or numerical simulation. In this paper, field instrumentation work carried out on a reinforced earth wall is described with the objective of capturing the essential behaviour of the wall during and after construction. Two different wall conditions were considered, that is, in the first case, the wall is allowed to move laterally and in the other case the wall is not flexible in transverse direction. Based on the observations made, it can be concluded that the locus of maximum tension is a vertical line offset approximately 0.35H away from the facing. For lateral pressure, it is seen that the curve for the flexible facing follows similar trend as the curve for the rigid facing except that the horizontal pressure at the flexible facing is generally slightly lower. Lastly, the connection ratio at rigid facing is generally higher than the connection ratio at the flexible facing. Key words: Reinforced earth, instrumentation, anchor blocks, lateral movement.

Behavior of cantilever and geosynthetic-reinforced walls on deformable foundations

A series of plane-strain model tests was performed to investigate the behavior of cantilever soil retaining walls (CWs) and geosynthetic-reinforced soil retaining walls with a rigid facing (GRS-RWs) placed on non-deformable and deformable foundations with various subgrade reaction moduli ( k v). The walls were designed to have configurations similar to those used in practice, with similar controlling safety factors against sliding. Screw jacks and springs were used to simulate undeformable and deformable grounds, respectively, with various maximum foundation settlements of S max ≒ 0, 2.5, 5, and 10% of the backfill height ( H). Test results show that the GRS-RW has better settlement-tolerating performances, in terms of the tilting angle ( θ), the horizontal displacement ( D h), and the settlement of the crest of the backfill ( D v1), than those of the CW. For both CWs and GRS-BWs, the worst scenario of the wall performance, in terms of D h, θ and D v1, occurred at a moderate foundation settlement of S max/ H ≒ 5% (or k v = 1.8 kPa/mm), rather than at a greater foundation settlement of S max/ H ≒ 10%, which facilitates a tilting-backward displacement mode. Experimental results also indicate that local lateral pressure coefficients against facing ( K f,z) for CWs may reach the at-rest (or K o) state at the central portion; values of K f,z may reach the passive (or K p) state at the lower portion of the wall. In the case of CWs, the measured values of local and global lateral pressure coefficients ( K f,z and K f) tend to increase with increasing maximum foundation settlement. This is not the case for GRS-RWs, which exhibited a relatively settlement-independent response, in terms of K f and K f,z, against facing. To develop relevant limit-equilibrium-based design methods for CWs and GRS-RWs placed on deformable foundations, knowledge of lateral pressure coefficients associated with various displacement and tilting induced by the foundation settlement are required.

A new type of integral bridge comprising geosynthetic-reinforced soil walls

ABSTRACT: Integral bridges, comprising a continuous bridge girder (i.e. deck) integrated to a pair of abutments without using hinged and movable shoes (i.e. bearings), have been constructed to alleviate several inherent drawbacks of conventional bridges. It is shown that this conventional type of integral bridge still has the following problems: (1) large residual settlements in the backfill, developing a bump immediately behind the abutments, and the development of high residual earth pressure on the back of the abutments by seasonal thermal expansion and contraction of the girder, as well as by traffic loads on the backfill; and (2) large detrimental deformation of the backfill by seismic loads. To alleviate these problems, it is proposed to reinforce the backfill with geosynthetic reinforcement that is firmly connected to the full-height rigid facings (i.e. abutments). A newly proposed integral bridge, called the GRS integral bridge, is constructed in stages: first, geosynthetic-reinforced backfill; second, pile foundations (if necessary); third, full-height rigid (FHR) facings (i.e. abutments); and finally a continuous girder integrated to the top of the two abutments, without using shoes. A series of static cyclic loading tests, laterally on the facing and vertically on the crest of the backfill, and shaking-table tests were performed on models of the conventional and new types of integral bridge, as well as two conventional bridge types comprising RC gravity-type abutments and geosynthetic-reinforced soil-retaining walls, both supporting a girder via shoes. The test results showed high static and dynamic performance of the GRS integral bridge, despite its simple structure and construction procedure, and therefore its low construction cost.

Simplified approach for assessing seismic displacements of soil-retaining walls. Part II: Geosynthetic-reinforced walls with rigid panel facing

Critical seismic coefficient ([Formula: see text]) and seismic displacement of some idealized geosynthetic-reinforced walls with full-height rigid panel facing (GRS-FHR walls) were calculated using a pseudo-static-based multi-wedge method in association with Newmark's sliding block theory. The proposed method uses experimentally verified lateral earth pressure coefficients to evaluate connection force at the facing/reinforcement interface subjected to various input seismic loadings. It was found that the values of critical seismic coefficient, [Formula: see text], can be expressed as linear functions of some dominant factors, such as the internal friction angle of backfill (ϕs) and the ratio between reinforcement length (L) and wall height (Ht). Empirical equations for the values of [Formula: see text] as functions of ϕs, L/Ht and other factors were established, and these equations were used in conjunction with seismic displacement evaluation methods proposed in this study. Based on the result of seismic displacement evaluations on a well-documented GRS-FHR wall that experienced the 1995 Hyogoken-Nambu earthquake, the effectiveness of the simplified approach for assessing seismic displacement of GRS-FHR walls was verified. These results were also compared with those calculated for some geosynthetic-reinforced walls with modular block facing that have been reported in a companion paper.

Influence of reinforcement parameters on the seismic response of reduced-scale reinforced soil retaining walls

The focus of the paper is on the influence of reinforcement design parameters (i.e. stiffness, length and vertical spacing) on the simulated earthquake response of reinforced soil retaining walls using reduced-scale model shaking table tests. A series of instrumented 1/6-scale model walls was constructed and dynamically loaded using a stepped-amplitude harmonic base acceleration record. The reinforcement design parameters investigated were found to have a significant effect on model response. Experimental results showed that the magnitude of accumulated facing lateral displacement under base excitation decreased with increasing reinforcement length, greater number of reinforcement layers and larger reinforcement stiffness. Significant down-drag forces at the back of the rigid facing were measured for all model configurations. However, the measured vertical load at the footing was not significantly influenced by changes in reinforcement parameters. The horizontal restrained (hinged) toe at the bottom of the rigid facing was shown to attract 30–60% of the total horizontal earth force depending on the reinforcement configuration. The magnitude and distribution of reinforcement connection loads was significantly affected by the reinforcement length, vertical spacing and stiffness. Measured footing loads, reinforcement connection loads and amplification factors are compared to values calculated using current practice in North America for geosynthetic reinforced soil walls and discrepancies between experimental results and design methods are identified. Implications of the physical test results to level of conservatism in current design practice are noted.

Seismic Displacement of a Geosynthetic-Reinforced Wall in the 1995 Hyogo-Ken Nambu Earthquake

ABSTRACT Seismic displacement of a geosynthetic-reinforced wall with full-height rigid panel facing (Tanata wall) in the 1995 Hyogo-ken Nambu earthquake is calculated using a pseudo-static method based on a 'multi-wedge' failure mechanism. The calculated value of horizontal displacement of the wall is comparable to the measured one. Based on an investigation into the effect of vertical ground acceleration to the seismic displacement of the wall using vertical and horizontal input ground accelerations in recorded seismograms, it is found that the contribution of vertical ground acceleration to the seismic displacement of the Tanata wall is small, because the peak horizontal and vertical ground accelerations are out of phase. Therefore, the use of peak vertical-to-horizontal ground acceleration ratio obtained in an earthquake event for pseudo-static multi-wedge analysis may overestimate the seismic displacement of a geosynthetic-reinforced wall to some extent. The effect of the embedment of the facing on the seismic displacement of the Tanata is also investigated. It is found that the effect of facing embedment to the seismic stability and/or displacement in the case of the Tanata wall is insignificant.

Experimental design, instrumentation and interpretation of reinforced soil wall response using a shaking table

A series of dynamic shaking table experiments were performed at the Royal Military College of Canada (RMC) to investigate the seismic performance of reduced-scale reinforced soil walls constructed with different toe boundary conditions, facing panel configurations and reinforcement layouts. The models were 1 m high by 1.4 m wide by 2.4 m long and were constructed with a full-height rigid panel facing, a uniform sand backfill and multiple layers of polymeric geogrid reinforcement. The wall toe was constructed to simulate a perfectly hinged toe (i.e. the toe allowed to rotate only) in one series of models and an idealised sliding toe (i.e. the toe allowed to rotate and slide horizontally) in the other series. The model walls were instrumented to measure facing panel and soil backfill lateral displacement, reinforcement strains, horizontal and vertical toe loads, and both facing and backfill acceleration response. All the models were subjected to a horizontal stepped-amplitude sinusoidal base acceleration input. The paper is focused on the experimental design, material properties, instrumentation and the interpretation of results. Selected test results are presented to illustrate typical model response features. Finally, some implications to current seismic design practice are identified with respect to magnitude and distribution of reinforcement-facing connection loads and the influence of a structural facing and restrained toe boundary condition on wall response during base excitation.

Behaviors of Several Types of Model Retaining Walls Subjected to Irregular Excitation

In order to establish practical design procedures to evaluate seismic stability of different types of retaining walls against high seismic loads, a series of shaking table tests were conducted with irregular excitation on retaining wall models consisting of six different types. Reinforced-soil retaining wall models with a rigid full-height facing exhibited a ductile behavior, when compared with conventional type retaining wall models such as gravity, leaning and cantilever-types. When the conventional type wall started to tilt, the subsoil reaction force at the toe of wall suddenly decreased due to the loss of bearing capacity. On the other hand, under similar conditions, the tensile force in the reinforcement of reinforced-soil walls could be mobilized effectively to resist overturning.

剛壁面補強土壁工法の壁面工に関する施工試験

剛壁面補強土壁工法の壁面工に関する施工試験