Geosynthetic-reinforced Soil Abutment Research Articles

Experimental and theoretical studies on deformation characteristics of Geosynthetic-Reinforced Soil (GRS) abutments induced by vertical loads

This study conducted five centrifuge model tests to investigate the deformation characteristics of the Geosynthetics Reinforced Soil (GRS) abutments under vertical loads, considering the setback distance ab and beam seat width B as two major influencing factors. Test results show that a linear correlation existed between the maximum lateral facing displacements DL and the maximum settlements at the top of the GRS abutments Dv. The ab and the B had different effects on the deformation characteristics of the GRS abutments as well as the relationship between the DL and the Dv. The total volumetric strains of the GRS abutments were smaller than 0.3% for all the cases investigated in this study, indicating that it was reasonable to use the assumption of zero-volume change for the deformation calculation of the GRS abutments. This study proposed an improved semi-empirical method to describe the relationship between the DL and the Dv. Centrifuge test results and data collected from the literature were used to validate the improved method. It was concluded that the improved method had the advantage of considering the effects of the ab and the B separately and therefore significantly improved the prediction accuracy of the deformations of the GRS abutments.

Ultimate bearing capacity of geosynthetic reinforced soil abutment centrifuge model tests

Five centrifuge models of geosynthetic reinforced soil (GRS) abutments with segmental block facing were loaded in the acceleration field under plane strain condition. Influencing factors including reinforcement tensile strength, setback and bearing area width were considered and analysed. Results show that the abutment with stronger reinforcement remained stable under the maximum loading capacity. However, abutments with weaker reinforcement showed excessive vertical strain, local deformation or even collapse. The ultimate bearing capacity increased with the lengthening of setback but decreased due to a larger bearing area. The rupture of reinforcements was observed and considered as the cause of the failures. Compared with the measured ultimate bearing capacity, the values calculated by the semi-empirical formula of design guidelines were significantly conservative. The failure surface of failed abutment developed from the rear edge of the bearing area to the middle height of the abutment at an angle of nearly 45° + φ/2. The setback and the bearing area width affected the form and position of the failure surface. The difference between the potential failure surface predicted by available methods and the measured failure surfaces has been discussed, and suggestions for the design and ultimate bearing capacity prediction of GRS abutments with segmental block facing are provided.

Cumulative deformation behavior of GRS bridge abutments under cyclic traffic loading

This paper presents an experimental study on reduced scale geosynthetic reinforced soil (GRS) abutment models subjected to cyclic traffic loading, aimed at investigating the influences of cyclic load amplitude, self-weight of bridge superstructure, and reinforcement vertical spacing on the cumulative deformations. The GRS abutment models were constructed using sand backfill and geogrid reinforcement. A static load was first applied to account for the self-weight of bridge superstructure, and then the cyclic loads were applied in several phases with increasing amplitude. The results indicate that significant cumulative footing settlement under cyclic loading mainly occurs within the first few hundred loading cycles, and the settlement increases with increasing cyclic load amplitude. The cyclic load amplitude and reinforcement vertical spacing have significant impacts on the cumulative deformations of GRS abutments under cyclic loading. The maximum facing displacement under cyclic loading occurs near the top of the wall. The cyclic load has a greater impact on the reinforcement strains near the upper middle reinforcement layers, while it has a smaller impact on the lower reinforcement layers.

Comparative assessment of stability of GRS abutments through 1 g physical model tests for field implementation

Geosynthetic reinforced soil (GRS) abutments have emerged as innovative improvement measures over the conventional GRS walls. Being an internally stabilized composite structure subjected to heavy stresses adjacent to facing, proper selection of GRS abutments in field is very important. Over the years, various design philosophies have been formulated in respect of GRS abutments but proper selection to a specific problem remains undiscussed. The present study attempts to conduct comparative analysis of stability of 5 types of chronologically evolved GRS bridge abutments (BA) namely BA I, BA II, BA III, BA IV and BA V through 1 g model tests (5 types are defined later) with special emphasis given to the influence of type of facing and configuration of reinforcements. A total of 75 model tests on 1/5th (N = 5) scaled down abutments have been performed to evaluate the effects of footing width (B), footing offset (x), facing type and abutment type on serviceable bearing capacity, ultimate bearing capacity, footing settlement, horizontal displacement of facing, tilting of footing, rotation and buckling of facing. The serviceability criteria based on FHWA recommendation has been chosen to ascertain field suitability of the model. An interesting mechanism correlating footing tilt (positive and negative) with movement of facing has been hypothesized and validated by the failure mode observed at the facing of the abutments. The abutments with modular facing were found to be more stable as compared to continuous facing. The footing width ratio (B/H) > 0.2 with footing offset ratio (x/H) > 0.3 (where, H is height of abutment) was found to be more suitable for field application. The degree of tilt, facing rotation, buckling behavior and differential settlement of footing were minimum for BA V. Based on all response parameters, BA V having modular facing with secondary reinforcements in the bearing bed performed exceedingly well in withstanding serviceable bearing pressures while sustaining larger footing settlements and resisting horizontal displacements of facing, followed by BA IV, BA III, BA II and BA I.

Scaled Model Tests Investigating Deformation Characteristics of Geosynthetic Reinforced Soil (GRS) Abutments under Vertical Loads.

This study conducted plane-strain scaled model tests to investigate the deformation characteristics of geosynthetic reinforced soil (GRS) abutments subjected to vertical loads. Setback distance, i.e., the distance between the back of the abutment facing and the front of the loading plate, was chosen as the investigated influencing factor since it is one of the most frequently used variables by engineers for the design of GRS abutments. This study analyzed the settlements at the top of the abutment, the lateral displacements of the abutment facing, and the volumetric deformations of the abutment under the applied vertical loads. Test results showed that increasing the setback distance could effectively reduce the deformations of the GRS abutment. There existed an optimum setback distance and further increasing the setback distance beyond this optimum value did not have a significant effect on reducing the abutment deformations. The vertical, lateral, and total volumetric deformations of the GRS abutment showed an approximately linear increase with the increase of the applied vertical loads. The lateral volumetric deformations of the GRS abutment were larger than its vertical volumetric deformations and therefore the total volumetric strains of the GRS abutment were not zero based on the test results. However, the theory of zero volume change may still be suitable for the deformation calculation of the GRS abutment since the values of the volumetric strains were minimal. The measured maximum lateral facing displacements were compared with the calculated values using the US Federal Highway Administration (FHWA) method, which assumes zero volume change of the GRS abutment under vertical loads. Comparison results indicated that the FHWA method overestimated the maximum lateral facing displacements of the GRS abutment under vertical loads. An improved method was proposed in this study to calculate the maximum lateral facing displacements under vertical loads based on the theory of zero volume change and a revised distribution of the settlements at the top of the GRS abutment. Results showed that the improved method could better predict the maximum lateral facing displacements as compared to the FHWA method.

Experimental study on the load bearing behavior of geosynthetic reinforced soil bridge abutments on yielding foundation

This paper presents an experimental study of the load bearing behavior of geosynthetic reinforced soil (GRS) bridge abutments constructed on yielding clay foundation. The effects of two different ground improvement methods for the yielding clay foundation, including reinforced soil foundation and stone column foundation, were evaluated. The clay foundation was prepared using kaolin and consolidated to reach desired shear strength. The 1/5-scale GRS abutment models with a height of 0.8 m were constructed using sand backfill, geogrid reinforcement, and modular block facing. For the GRS abutments on three different yielding foundations, the reinforced soil zone had relatively uniform settlement and behaved like a composite due to the higher stiffness than the foundation layers. The wall facing moved outward with significant movements near the bottom of facing, and the foundation soil in front of facing showed obvious uplifting movements. The vertical stresses transferred from the footing load within the GRS abutment and on the foundation soil are higher for stiffer foundation. The improvement of foundation soil using geosynthetic reinforced soil and stone columns could reduce the deformations of GRS abutments on yielding foundation. Results from this study provide insights on the practical applications of GRS abutments on yielding foundation.

Predicting and validating the load-settlement behavior of large-scale geosynthetic-reinforced soil abutments using hybrid intelligent modeling

Settlement prediction of geosynthetic-reinforced soil (GRS) abutments under service loading conditions is an arduous and challenging task for practicing geotechnical/civil engineers. Hence, in this paper, a novel hybrid artificial intelligence (AI)-based model was developed by the combination of artificial neural network (ANN) and Harris hawks’ optimisation (HHO), that is, ANN-HHO, to predict the settlement of the GRS abutments. Five other robust intelligent models such as support vector regression (SVR), Gaussian process regression (GPR), relevance vector machine (RVM), sequential minimal optimisation regression (SMOR), and least-median square regression (LMSR) were constructed and compared to the ANN-HHO model. The predictive strength, relalibility and robustness of the model were evaluated based on rigorous statistical testing, ranking criteria, multi-criteria approach, uncertainity analysis and sensitivity analysis (SA). Moreover, the predictive veracity of the model was also substantiated against several large-scale independent experimental studies on GRS abutments reported in the scientific literature. The acquired findings demonstrated that the ANN-HHO model predicted the settlement of GRS abutments with reasonable accuracy and yielded superior performance in comparison to counterpart models. Therefore, it becomes one of predictive tools employed by geotechnical/civil engineers in preliminary decision-making when investigating the in-service performance of GRS abutments. Finally, the model has been converted into a simple mathematical formulation for easy hand calculations, and it is proved cost-effective and less time-consuming in comparison to experimental tests and numerical simulations.

Experimental study on the load bearing behavior of geosynthetic reinforced soil bridge abutments with different facing conditions

This paper presents an experimental study on reduced-scale model tests of geosynthetic reinforced soil (GRS) bridge abutments with modular block facing, full-height panel facing, and geosynthetic wrapped facing to investigate the influence of facing conditions on the load bearing behavior. The GRS abutment models were constructed using sand backfill and geogrid reinforcement. Test results indicate that footing settlements and facing displacements under the same applied vertical stress generally increase from full-height panel facing abutment, to modular block facing abutment, to geosynthetic wrapped facing abutment. Measured incremental vertical and lateral soil stresses for the two GRS abutments with flexible facing are generally similar, while the GRS abutment with rigid facing has larger stresses. For the GRS abutments with flexible facing, maximum reinforcement tensile strain in each layer typically occurs under the footing for the upper reinforcement layers and near the facing connections for the lower layers. For the full-height panel facing abutment, maximum reinforcement tensile strains generally occur near the facing connections.

Numerical study of geosynthetic reinforced soil bridge abutment performance under static and seismic loading considering effects of bridge deck

Although the use of Geosynthetic Reinforced Soil (GRS) bridge abutments has been increasing, the seismic performance of such structures has remained a significant concern due to their unknown behavior in load-bearing and stress distribution under bridge load and seismic conditions simultaneously. This paper investigates the static and dynamic response of GRS bridge abutment. A series of numerical models representing the realistic field conditions of these structures, including two reinforced soil walls and a single span deck that restrains the top of walls, rather than equivalent surcharge load, was developed. The calibrated numerical model in FLAC program was used to evaluate the effects of horizontal restraint from the deck on the GRS wall displacements and reinforcement loads at the end of construction and under harmonic base acceleration up to 0.5 g. Results indicated that the restraint mobilized from the bridge deck presence, considerably affected the results at both the end of construction and after the dynamic load was applied. Moreover, a series of the parametric studies were performed to investigate the influences of backfill soil relative compaction, reinforcement stiffness, reinforcement length, and reinforcement vertical spacing on the response of GRS abutments at the end of construction and post dynamic state.

Evaluation of vertical stress distribution in field monitored GRS-IBS structure

This paper presents a case study of a geosynthetic-reinforced soil (GRS) integrated bridge system (IBS) in which the vertical stresses during and after construction were monitored via instrumentation. The purpose of the study was to evaluate the effects of reinforcement spacing, width of the beam seat, and seasonal variations on the vertical stresses measured in the field. The stress distribution observed in the field was also compared to the theoretically estimated stress distribution. The results showed that the bearing bed where the reinforcements are doubled is effective in reducing the applied stresses by about 1.8 to 5.4 times. The width of the beam seat controlled the magnitude of the applied stresses on the GRS abutment and the applied stress was vertically transferred all the way to the foundation level even in wider beam seats. A comparison between field recorded and theoretical stress values showed that the Boussinesq method provides a better estimate of the field vertical stress distribution than the approximate 2 : 1 method, although the 2 : 1 method provides more conservative stresses to be considered for design. Results from long-term monitoring indicated that vertical stress distribution in the GRS abutments was not significantly influenced by seasonal variations.

Responses of geosynthetic-reinforced soil (GRS) abutments under bridge slab loading: Numerical investigation

Abstract This study evaluated the responses of geosynthetic-reinforced soil (GRS) abutments subjected to bridge slab loading under working stress conditions using two-dimensional finite difference numerical software. A parametric study was conducted to investigate the effects of different combinations of reinforcement spacing Sv and reinforcement stiffness J, beam seat width b, and setback distance ab on the responses of the GRS abutments in terms of additional vertical stresses under the beam seat centerline Δσv induced by the bridge slab load, additional lateral earth pressures behind the abutment facing Δσh-facing and under the beam seat centerline Δσh-cetner induced by the bridge slab load, and maximum tension in the reinforcement Tmax. Numerical analyses evaluated trapezoidal and uniform reinforcement layouts and showed that both reinforcement layouts generated similar responses of the GRS abutments. Under the same ratio of J/Sv, different combinations of Sv and J generated similar distributions of Δσv, Δσh-facing and Δσh-center. The maximum of Tmax with depth decreased almost proportionally with the decrease of Sv. Larger b and ab caused lower Δσv, Δσh-facing, Δσh-center, and smaller Tmax in the upper reinforcement layers. The truncated 2 to 1 distribution method, which considers the effects of abutment facing on the Δσv distribution, could reasonably predict the Tmax in the reinforcement.

Passive Force–Displacement Behaviour of GRS Bridge Abutments

Many bridge abutments suffered severe damages due to pounding of superstructure elements of the bridge during seismic excitation. Collision of the girder is resisted by passive pressures mobilised in the backfill soils. Seismic load on the bridge structure causes the bridge abutments to undergo lateral translation (Δ) and rotation. The present study focuses on the evaluation of passive force (Pp) developed in the reinforced backfills of the geosynthetic-reinforced soil (GRS) bridge abutments. The GRS abutments of nine configurations with three different geogrid spacing and three different geogrid lengths are modelled using finite element (FE) approach under lateral push. Hypoplastic soil constitutive model with inter-granular strain concept is used to model the soil behaviour. User material subroutine, VUMAT is developed to simulate the soil behaviour in Abaqus. The maximum passive resistance (Pp,ult) increases by 12% in the GRS abutments with closer geogrid spacing.

Seismic Behavior of GRS Bridge Abutments with Concrete Block Facing: an Experimental Study

Despite great promise of excellent performance characteristics of geosynthetic reinforced soil (GRS) bridge abutments under static loads, their response under earthquake loading remains a concern. In order to advance and implement this new technology, especially in seismically active regions, this study was undertaken to examine the performance of GRS bridge abutments under seismic loads in a rational and critical manner and to present rational guidelines for design and construction of earthquake-resistant GRS bridge abutments. This paper reports a field-scale shake table test that was performed to provide relevant data for validate an analytical procedure for GRS abutments. The abutment model withstood vertical and horizontal loads placed on it during ground accelerations of 0.15 g at 1.5 Hz and did not experience structural failure or significant movement. The model sufficiently withstood the bridge loads while being subjected to ground accelerations up to 1.0 g at 3 Hz. This paper describes the instrumented field-scale GRS bridge abutment shake table test and reports the test results.

Seismic Behavior of Geosynthetic-Reinforced Soil (GRS) Bridge Abutments with Concrete Block Facing—an Analytical Study

The response of GRS bridge abutments to earthquake loading remains a concern despite their great success under static loads. In order to advance and implement this new technology, especially in seismically active regions, the study described in this paper and the companion paper was undertaken to examine the performance of GRS bridge abutments under seismic loads in a rational and critical manner. In this study, a field-scale shake table test was performed in order to provide relevant test results to validate an analytical procedure for GRS abutments that was used subsequently to perform a rigorous parametric analysis that formed the basis for the proposed guidelines for design and construction of earthquake-resistant GRS abutments. This paper describes the validation of a finite element model where its analytical results were compared with the results of the instrumented GRS bridge abutment shake table test described in the companion paper titled: “Seismic behavior of geosynthetic-reinforced soil (GRS) bridge abutments with modular-block facing—an experimental study.” After validation is achieved, the finite element modeling was used to perform rigorous parametric analyses on a bridge with GRS abutments subjected to various types of earthquake loading.

A method for correcting field strain measurements to account for temperature effects

Measurements of deformation and strain are of critical importance for the structural health monitoring of geosynthetic reinforced soil (GRS) structures. For some commonly used wiring configurations and sensors, field strain measurements can exhibit apparent strains that are caused by changes in wire temperature or changes in gauge temperature, which do not correspond to changes in actual strain in the geosynthetic. Correcting for these effects is important for separating out real structural behavior from wiring and sensor issues, and is imperative for avoiding false trigger warnings in automated instrumentation reporting systems. The current paper consequently presents a method for correcting field strain measurements to account for temperature effects. Data collected from sensors embedded in a heavily-instrumented GRS abutment over a two-year monitoring period is presented. The distributed thermistor array embedded in the GRS abutment is shown to be particularly useful for understanding temperature effects on the measured foil strain gauge data. The presented approach and associated framework for data correction are useful for practicing engineers and other researchers, as the general concepts from this study can be applied to data collected from many instrumented geosynthetic field projects.

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.

Numerical Investigation of Geosynthetic-Reinforced Soil Bridge Abutments under Static Loading

AbstractThis paper presents a numerical investigation of the performance of geosynthetic-reinforced soil (GRS) bridge abutments under static loading conditions. Simulations were conducted using a finite-difference program to model the Founders/Meadows GRS bridge abutment during construction and service. Simulated results are in good agreement with field measurements, including displacements, lateral and vertical earth pressures, and tensile strains and forces in reinforcement. The simulations also indicate that horizontal restraint from the bridge structure has a significant influence on abutment deflections. A parametric study was then conducted to investigate the performance of a single-span full bridge system with two GRS abutments, including effects of bridge contact friction coefficient, backfill soil relative compaction, backfill soil cohesion, reinforcement spacing, reinforcement length, reinforcement stiffness, and bridge load. Results indicate that backfill soil relative compaction, reinforcement...

Experimental study on performance of geosynthetic-reinforced soil model walls on rigid foundations subjected to static footing loading

Geosynthetic-reinforced soil (GRS) walls have been increasingly used to support bridge foundations as abutment walls. On the GRS abutment wall, large footing loads are applied adjacent to the wall facing. However, so far limited studies have been conducted to investigate the performance of GRS abutment walls subjected to static or dynamic loading. This study presents a series of model tests on the GRS walls to evaluate the effects of several influence factors, including the offset distance of a strip footing, the width of the strip footing, the length of geogrid reinforcement, and the connection mode between geogrid and facing, on the ultimate bearing capacities of the strip footings on the GRS walls. The settlements of the loading plate and the lateral displacements of the wall facing during loading were monitored. Thin colored sand layers were placed in the backfill sand to observe possible failure surfaces developing in the GRS walls. The experimental results showed that the footings on the GRS walls with 0.7H (H is the wall height) long reinforcement reached the maximum bearing capacities at the offset distances of 0.3H and 0.4H in the wall tests with mechanical and frictional connections, respectively. When the GRS walls had the geogrids with longer reinforcement length (2H), the ultimate bearing capacity increased with the offset distance of the footing and became constant when the offset was greater than 0.4H. It was observed that the failure surface started from the edge of the footing and exited from the facing of the wall. Based on the limit equilibrium analyses, under the footing loading, the slip surfaces by Spencer's two-part wedge method had a good agreement with those observed in the model tests.

Mini-Pier Testing To Estimate Performance of Full-Scale Geosynthetic Reinforced Soil Bridge Abutments

The geosynthetic reinforced soil (GRS) performance test (PT), also called a mini-pier experiment, was developed by the Federal Highway Administration (FHWA) to evaluate the material strength properties of GRS composites built with a unique combination of reinforcement, compacted fill, and facing elements. The PT consists of constructing a 1.4-m square column of alternating layers of compacted granular fill and geosynthetic reinforcement with a facing element that is frictionally connected up to a height of 2 m, then axially loading the GRS mass while measuring deformation to monitor performance. The results can be directly used in the design of GRS abutments and integrated bridge systems. Considering that the geometry of the PT is square in plan, the equivalency of the results to a bridge application, which more resembles a plane strain condition, is evaluated and presented in this paper. The analysis indicates that the PT closely approximates the bearing resistance, or capacity, of a typical GRS abutment, and is a conservative estimate when predicting stiffness. These results indicate that the PT can be used as a design tool for GRS abutments at both the strength and service limit states.

Rapid Replacement

To replace a two-lane bridge nearing the end of its design life, the Delaware Department of Transportation used an innovative approach. Built using geosynthetic reinforced soil abutments and prefabricated bridge superstructure elements, the composite bridge was constructed rapidly and has been equipped with a custom-designed instrumentation system to monitor long-term performance.