Geosynthetic-reinforced Soil Retaining Walls Research Articles

Long-Term Performance Assessment of a Geosynthetic-Reinforced Railway Substructure

Significant savings in carbon emissions, cost, and time could be achieved via the reduction in maintenance frequency, capital costs of track construction, and land used. Geosynthetic-reinforced soils offer such sustainable solutions. The experimental work presented in this paper investigates the long-term performance of a Geosynthetic-Reinforced Soil Retaining Wall (GRS-RW) system as an alternative to the conventional railway embankment. Full-scale testing was carried out on three sleeper sections of ballasted and slab tracks by simulating train loads cyclically, phased to 360 km/h. The tracks were supported by either a low-level fully confined conventional embankment or a GRS-RW substructure. The substructures were formed of a 1.2 m deep subgrade and frost protection layer, in accordance with high-speed railway design standards. The overall aim was to assess the performance of the tracks, in terms of transient displacements and total settlements. It was observed that once the GRS-RW system reached its active state, it deformed in a very similar way to a conventional embankment despite the fact that the GRS-RW system is less confined than the conventional embankment. The results indicate that the cumulative settlement of the slab track, which is due to the plastic deformation of the soil, is significantly less than that of the ballasted track, which is primarily caused by the movement of the ballast particles.

Analytical Solutions for Internal Stability of a Geosynthetic-Reinforced Soil Retaining Wall at the Limit State

Analytical Solutions for Internal Stability of a Geosynthetic-Reinforced Soil Retaining Wall at the Limit State

Centrifuge modeling of geosynthetic-reinforced soil retaining walls subjected to the combined effect of earthquakes and rainfall

Local fine-grained soils were usually used as backfill for geosynthetic-reinforced soil retaining walls (GSRWs). However, there are few studies on the seismic response in this case, especially under the influence of rainfall. In this study, three centrifuge shaking table tests were performed at 30 gravities to investigate the performance of GSRWs subjected to the combined effect of earthquakes and rainfall. Two stages were designed in this study. In the first stage, three conditions were simulated, i.e., post-rainfall earthquake (Test-1), rainfall and earthquake occurring simultaneously (Test-2), and post-earthquake rainfall (Test-3). The results show that if there was enough time for rainwater seepage, the suction force generated in unsaturated GSRW enhanced the soil strength. When GSRW was subjected to heavy rainfall and no time for seepage, the deformation of the GSRW was largest due to the high excess pore water pressure of local saturated soil in GSRW. In the second stage, seismic failure models of GSRWs with different water contents were studied. Under the excitation of a series of continuous earthquakes, a large tensile crack was formed in the unsaturated GSRW, whereas no cracks were found in the saturated GSRW, but its panel demonstrated a large bulging deformation.

Stress distribution in reinforced railway structures

This paper evaluates the performance of a geosynthetic reinforced soil retaining wall (GRS-RW) system as an alternative to a conventional railway embankment. The aim is to investigate the behaviour of the GRS-RW system in terms of displacements and stress levels at different locations in the track and substructure. Full-scale laboratory experimental testing is carried out on a GRS-RW structure, supporting sections of ballasted and slab track, under moving loads at 360 km/h. The tracks are supported by a low-level fully confined conventional embankment and a GRS-RW system, which are constructed to high-speed standards. Displacement transducers and earth pressure cells are placed at different locations to record the displacements of the track and the stress levels in the substructure. The test results show that the pressure levels on the GRS-RW wall are negligibly small for the particular test setup, proving the GRS structure under the action of compaction reached its active state. This means that the reinforced soil was self-supporting under its self-weight and train loads, meaning there was minimal pressure on the walls. Therefore, GRS-RW systems are better alternatives to traditional earth embankments due to enhanced soil stabilisation and less land take.

Design Theory and Method of Geo-Synthetic Reinforced Soil Retaining Wall Combined with a Gravity Retaining Wall or Full Height Rigid Facing

Geo-synthetic reinforced soil retaining wall (GRS-RW) combined with a Gravity Retaining wall (GRW) facing or Full High Rigid (FHR) facing is a new type of retaining wall. This type of retaining wall is used to get full advantages of GRW and reinforced soil retaining wall (RS-RW) and to avoid their drawbacks. The design method based on the principle of working strain considers the backfill in the limit state but the reinforcement not in the limit state; while in traditional design method based on the tensile strength of reinforcement, consider both backfill and reinforcements in the limit state and it cannot reflect the influence of reinforcement stiffness. In this paper, numerical analyses were performed to evaluate the stress and strain of both reinforcement and backfill. From the analyses, deformation of the retaining wall, the working performance of GRS-RW with GRW facing, and contribution of geo-grids to GRS-RW with a GRW facing, were evaluated. Analyses are performed for determining the force between GRS-RW with a GRW facing and reinforced soil. Analytical methods, for the calculation of soil pressure acting on the back of GRW, based on the principle of working stress are obtained by comparative analysis between the working performance characteristics of common GRS-RW and GRS-RW with GRW facing. A new analytical method for determining the force between GRS-RW with a GRW facing and reinforced soil “E” is proposed. By comparative study between theoretical and numerical analysis results, method 1 and method 2 are recommended for determining the “E”. A method for determining the tension in the reinforcement of GRS-RW with a GRW facing based on the principle of working strain is also presented in this paper.

Geosynthetic-reinforced soil structures for railways and roads: development from walls to bridges

The development and construction of various types of geosynthetic-reinforced soil (GRS) structures for railways, roads and others, mainly for railways, for the last 35 years in Japan is described. In the 1980s, GRS retaining wall (RW) with full-height rigid (FHR) facing was developed. The FHR facing is constructed firmly connected to reinforcement layers after the reinforced backfill and subsoil has deformed sufficiently. In the early 1990s, GRS Bridge Abutment supporting one end of a simple girder at the top of the FHR facing was developed. In the early 2000s, GRS Integral Bridge was developed, which structurally integrates both ends of a continuous girder to the top of the FHR facings of a pair of GRS RWs. The total wall length of these GRS structures became about 185 km by June 2019 with no problematic case. The use of FHR facing, the staged construction of FHR facing and the structural integration for GRS Integral Bridge are the three major breakthroughs for the development of these GRS structure technologies.

Behaviour of Two-Tiered Geosynthetic-Reinforced Soil Walls

The literature studies and current design methodologies of reinforced soil wall show increases in tensile stresses in reinforcement with increase in height of wall. This results in decrease of spacing between reinforcement and ultimately increases in cost of construction. Alternatively, the reinforced soil wall can be constructed in tiered fashion to improve aesthetic and reduce cost of construction. This paper focuses on the performance of two-tiered-reinforced soil-retaining walls with different offset lengths. A numerical model of geosynthetic-reinforced soil-retaining wall with a concrete-block facing reported in literature is simulated using commercial finite element software ANSYS. The backfill soil is modelled using the Drucker–Prager plasticity model. The concrete facing is simulated as elastic material and reinforcement with non-linear material properties. The results obtained from numerical model are validated with those from physical model studies reported in literature. Using validated model parameters, two-tiered-reinforced soil walls with different offset lengths are simulated. Four models of 0 offset, 1.2-m offset, 2.0-m offset and 3.0-m offset are developed to study the effects of tiered wall. The offset lengths are determined as intermediate offset distance and large setback distance as per FHWA (2010). The walls are studied for horizontal displacement of facing, strain developed in backfill soil and in reinforcement layers. The maximum horizontal displacements of reinforced soil wall decrease with increase in offset length of tiered wall. By considering the strain variation in soil, two deformation zones—shear deformation zone near the facing and compaction zone below the upper tier facing—are identified. The strains in compaction zone of lower tier increase with increase in offset length. The reinforcement strains in top reinforcement layer of lower tier decrease with increase in offset length.

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.

Computational simulation of time-dependent behavior of soil–structure interaction by using a novel creep model: Application to a geosynthetic-reinforced soil physical model

In this paper, a model geosynthetic-reinforced soil retaining walls (GRS-RW) is tested by vertically loading it through a rough footing on the top near the retaining wall and the results are simulated by a sophisticated nonlinear Finite Element Method (FEM) having a novel rate dependent constitutive model for both the backfill material and the geosynthetic reinforcement. Usually, polymer geosynthetic reinforcement is known to exhibit more-or-less rate-dependent stress–strain or load–strain behavior due to their viscous properties. The geomaterials (i.e., clay, sand, gravel and soft rock) also exhibit viscous properties. The viscous behavior of geometrials are quite different from that of the polymer based geosynthetic-reinforcements. It has been revealed recently that viscous behavior of sand is a kind of temporary effect, which vanishes with time. So the rate-dependent deformation of backfill reinforced with polymer geosynthetic reinforcement becomes highly complicated due to interactions between the elasto-viscoplastic properties of backfill and reinforcement. In the present study, a scaled model geosynthetic-reinforced soil retaining wall is tested with a vertically loaded rough rigid footing. The results of the model test are simulated by using an appropriate elasto-viscoplastic constitutive model of both sand and geogrid embedded in a nonlinear plane strain FEM.

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.

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.

FEM Simulation of Earth Pressure on Geosynthetic-Reinforced Soil Retaining Wall under Variable Rate Loading

On the basis of the Dynamic Relaxation method, a nonlinear finite element method (FEM) analysis procedure was developed for the geosynthetic-reinforced soil retaining wall. The FEM procedure technique incorporated the unified three-component elasto-viscoplastic constitutive model which can consider the rate-dependent behavior of both the backfill soil and the geosynthitic reinforcement. A simulation was performed on a physical model test on geosynthetic-reinforced soil retaining wall to validate the presented FEM. Extensive finite-element analyses were carried out to investigate the earth pressure distributions from the back of retaining wall under variable rate loading. It is shown that this FEM can well simulate the rate-dependent behavior and the earth pressure of geosynthetic-reinforced soil retaining wall.

FEM Analysis on Tensile Force of Geosynthetic Reinforcement Arranged in GRS-RW Considering Variable Loading Rate

The combined effects of the rate-dependent behavior of both the backfill soil and the geosynthetic reinforcement have been investigated, which should be attributed to the viscous property of material. A nonlinear finite element method (FEM) analysis procedure based on the Dynamic Relaxation method was developed for the geosynthetic-reinforced soil retaining wall (GRS-RW). In the numerical analysis, both the viscous properties of the backfill and the reinforcement were considered through the unified nonlinear three-component elastic-viscoplastic model. The FEM procedure was validated against a physical model test on geosynthetic-reinforced soil retaining wall with granular backfill. Extensive finite-element analyses were carried out to investigate the tensile force distributions in geosynthetic reinforcement of geosynthetic-reinforced soil retaining wall under the change of loading rate. It is found from the analyses that the presented FEM can well simulate the rate-dependent behavior of geosynthetic-reinforced soil retaining wall and the tensile force of geosynthetic reinforcement arranged in retaining wall.

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.

Evaluation of Geosynthetic Forces in GRSRW under Dynamic Condition

Geosynthetics have proved to be suitable for reinforced soil retaining walls. Based on the increasing uses of geosynthetic reinforced soil systems in the regions, which bear frequent earthquakes, the study of dynamic behavior of structures seems necessary. Determining the reinforcement forces is; therefore, one of the most important and main points of discussions in designing retaining walls, by which we prevent from conservative planning. Thus, this paper intended to investigate the effects of such parameters as wall height, acceleration type, vertical spacing of reinforcement, type of reinforcement and soil type on forces and deformation through numerical modeling of the geosynthetic reinforced soil retaining walls (GRSRW) under dynamic loading with finite difference method by using FLAC. The findings indicate rather positive results with each parameter.

Dynamic stability of geosynthetic-reinforced soil integral bridge

ABSTRACT: To evaluate the dynamic stability of different bridge types, the results from a series of shaking-table tests on small-scale models of the following bridge types were analysed within the framework of the single-degree-of-freedom theory: (1) a conventional bridge (CB), comprising a girder (i.e. deck) supported via a pair of movable and fixed bearings (i.e. shoes) by gravity-type abutments (without a pile foundation) having unreinforced backfill; (2) a GRS-RW bridge, comprising a girder supported via a pair of movable and fixed bearings by a pair of sill beams placed on the crest of a pair of geosynthetic-reinforced soil-retaining walls (GRS-RWs) having a stage-constructed full-height rigid facing; (3) an integral bridge (IB), comprising a girder integrated to a pair of abutments (without bearings) and unreinforced backfill; (4) a GRS integral bridge, comprising a girder integrated to the abutments (in the same way as the IB bridge) while the backfill is reinforced with geosynthetic layers connected to the facings (in the same way as the GRS-RW bridge); and (5) a GRS integral bridge with a cement-mixed soil zone of rectangular prismatic or trapezoidal shape immediately behind the facing. The following is shown: the stability of the bridge against dynamic excitations increases: (1) with an increase in the initial natural frequency via an increase in the initial stiffness; (2) with a decrease in the decreasing rate of stiffness during cyclic loading (i.e. an increase in the dynamic ductility); (3) with an increase in the damping energy dissipation capacity near and at failure; and (4) with an increase in the dynamic strength. With the GRS integral bridge, the structural integration and geosynthetic-reinforcing of the backfill, as well as cement-mixing of the backfill immediately behind the facings, all contribute to the evolution of these four factors. The natural frequency can then always be kept much higher than the predominant frequency of ordinary design earthquake motion, the response acceleration is kept sufficiently low, and the dynamic stability can be kept very high.

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.

Numerical analysis of reinforced soil-retaining wall structures with cohesive and granular backfills

The failure mechanisms of reinforced soil segmental walls with extensible reinforcements were studied by performing a numerical analysis using the finite element method. The numerical approach was first verified against the results of three instrumented full-scale structures reported in the literature. Finite element models with different combinations of reinforcement spacing, reinforcement length and backfill soil were analysed. The ϕ–c reduction method, which is a special shear strength parameter reduction technique, was applied to simulate the failure conditions. The results of ϕ–c reduction analysis were used to evaluate assumptions used in current design procedures for geosynthetic-reinforced soil walls. In particular, shear strains were used to identify failure surfaces. Interpretation of the results indicated that, for both granular and cohesive backfills, the potential failure surface gradually shifts to a direct sliding mode as the system approaches failure. As a result, under working loads the potential failure surface used in current design analysis is correct, but the failure plane of a geosynthetic-reinforced soil-retaining wall at failure approaches a direct sliding type or a bilinear plane, which starts from the toe of the wall with a very shallow slope.

Unified Elastoplastic–Viscoplastic Bounding Surface Model of Geosynthetics and Its Applications to Geosynthetic Reinforced Soil-Retaining Wall Analysis

The static and dynamic behaviors of reinforced soil structures are possibly subjected to the effects of creep or stress relaxation due to the time-dependent behavior of geosynthetic inclusions and backfill. To simulate the time-dependent monotonic and cyclic behavior of geosynthetics, an isothermal constitutive model is formulated within the framework of elastoplasticity–viscoplasticity. The concept of bounding surface plasticity is first utilized to formulate a time-independent cyclic model of geosynthetics. In order to capture the hardening stiffness of some polyester geosynthetics, an exponential bounding curve is used in simulating the primary loading. The time-independent version of the model was extended into an elastoplastic–viscoplastic model using overstress viscoplasticity with reference to available experimental data. The model was evaluated using creep, stress relaxation, monotonic, and cyclic loading test results obtained for different geosynthetics. It was then incorporated into a finite-ele...