No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Geosynthetic Reinforced Soil Performance Testing- Axial Load Deformation Relationships
Abstract
FOREWORD The use of geosynthetic reinforced soil (GRS) for load bearing applications such as bridge abutments and integrated bridge systems (IBS) has expanded among transportation agencies looking to save time and money while delivering a better and safe product to the traveling public. GRS has been identified by the Federal Highway Administration (FHWA) as a proven, market-ready technology, and is being actively promoted through its Every Day Counts (EDC) initiative. FHWA interim design guidance for GRS abutments and IBSs is presented in Publication No. FHWA-HRT-11-026. The guidance includes the procedure and use of the GRS performance tests, also termed a mini-pier experiment. This report presents a database of nineteen performance tests performed by the FHWA, largely at the Turner-Fairbank Highway Research Center. It also presents findings, conclusions, and suggestions regarding various design parameters related to the performance of GRS, such as backfill material, reinforcement strength, reinforcement spacing, facing confinement, secondary reinforcement, and compaction. A reliability analysis for load and resistance factor design (LRFD) was performed based on the results of this performance testing to determine a calibrated resistance factor for the soil-geosynthetic capacity equation. The results of this analysis can also be used by bridge designers to estimate capacity and deformation of GRS. In addition, an insight into the behavior of GRS as a new composite material due to the close reinforcement spacing is described.
... GRS mini-pier test is a test method developed by the Federal Highway Administration (FHWA) to investigate the load-deformation behavior of a frictionally connected GRS mass [31,32]. A GRS mini-pier is composed of multiple components, such as compacted backfill, closely spaced geosynthetic layers, and hollow Concrete Masonry Unit (CMU) facing blocks. ...
... Therefore, the GRS mini-pier test is an excellent example to assess different interaction simulation methods on the predicted performance of GRS structures. The mini-pier test TF6 conducted by Nicks et al. [31] was chosen as the prototype testing of the numerical investigation to assess different interaction simulation methods. The TF6 mini-pier was 2 m high and composed of ten layers of CMU blocks. ...
... In all three numerical models, the backfill soil VDOT21A aggregate was modeled with the linearly elastic perfectly plastic MC constitutive model. A friction angle ϕ of 53° and a cohesion c of 5.5 kPa were adopted in the numerical model based on large-scale direct shear test results reported by Nicks et al. [31]. A dilation angle ψ of 23° was used. ...
The purpose of this study is to assess effects of two different simulation methods (i.e., interfaces with a single spring-slider system and interfaces with double spring-slider systems) for interactions between reinforcement and the surrounding medium on the performances of geosynthetic-reinforced soil (GRS) structures when conducting numerical analyses. The fundamental difference between these two methods is the number of the spring-slider systems used to connect the nodes of structural elements simulating the geosynthetic reinforcement and the points of solid grids simulating the surrounding medium. Numerical simulation results of pull-out tests show that both methods reasonably predicted the pullout failure mode of the reinforcement embedded in the surrounding medium. However, the method using the interfaces with a single spring-slider system could not correctly predict the interface shear failure mode between the geosynthetics and surrounding medium. Further research shows that these two methods resulted in different predictions of the performance of GRS piers as compared with results of a laboratory load test. Numerical analyses show that a combination of interfaces with double spring-slider systems for reinforcement between facing blocks and interfaces with a single spring-slider system for reinforcement in soil resulted in the best performance prediction of the GRS structures as compared with the test results. This study also proposes and verifies an equivalent method for determining/converting the interface stiffness and strength parameters for these two methods.
... The equation was derived based on an inferred assumption that there was significant interaction between the soil and geosynthetic reinforcement in the soil mass [31]. Equation (1) was validated by at least 15 available field-scale experiments, if which some of them were conducted by the Federal Highway Administration [32], for materials with properties falling in the range of 10 mm < d max < 33 mm and 6 < S v /d max < 20. It is unclear whether the accuracy of the equation would still be consistent in materials with properties falling outside the above ranges, for example, for the case with the maximum aggregate size of 33 mm and S v /d max = 3. ...
... According to the Mohr-Coulomb failure criterion, failure occurs on the plane with the maximum ratio of shear stress and normal stress; thus, the theoretical inclination angle θ of the Rankine active wedge is (45 o + φ /2), leading to a backcalculated internal friction angle of 35.4 • , which is smaller than the peak internal friction angle of 50 • obtained from a series of 150 mm diameter by 300 mm high triaxial tests performed on unreinforced soil. A similar result was also observed in [32]. Based on the rupture pattern of the geotextiles in their test specimen no. ...
... Based on the rupture pattern of the geotextiles in their test specimen no. TF-6 and an inclination angle of 62.9 • , Nicks et al. [32] obtained a backcalculated internal friction angle of 35.8 • , which was 25% smaller than the peak internal fiction angle obtained from the triaxial test of unreinforced soil. At first, one may argue that the shear strength of soil decreased with an increase in the specimen size [48] and hence the 2 m high by 1.4 m wide SGC mass should possess a smaller angle of friction than that measured from the medium size (150 mm diameter by 300 mm high) triaxial apparatus. ...
There is an increasing awareness on the major benefits of using soil-geosynthetic composite (SGC) to achieve and maintain the stability of earth-filled embankment. Unlike the mechanically stabilized earth wall, the mechanism of the composite mass is still not fully understood. For examples, current analyses have been limited to an SGC mass with a reinforcement spacing Sv of 0.2 m only; the combined effect of reinforcement and backfill properties is rarely studied; the equation for the estimation of the load-carrying capacity of the SGC mass has only been validated for backfill with maximum particle size dmax between 10 mm and 33 mm and an Sv/dmax ratio between 6 and 20. The consequences of backfill compaction on an SGC mass with different reinforcement spacings are yet to be validated and whether the load-carrying capacity equation would still be applicable for materials with properties falling outside the above ranges. Through the simulation and validation of a field scale SGC mass, this study aims to assess the influence of various reinforcement and backfill parameters on the mechanical responses of a large-scale experimental SGC mass under its working load and failure conditions; the results are presented in terms of the wrapped face lateral displacement, reinforcement axial strain, and load-carrying capacity.
... Test program for the GSGC tests [46] Table 3 Effects of CMU facing on stiffness and capacity [44] . Table 4 NCHRP full-scale test results [15] Table 5 Recommended allowable bearing pressure of a geosynthetic reinforced soil abutment with an integrated sill [15] . ...
... Table 4 NCHRP full-scale test results [15] Table 5 Recommended allowable bearing pressure of a geosynthetic reinforced soil abutment with an integrated sill [15] . Table 6 Comparison between GMSE and GRS design methods [44] Table 8 Comparison between predicted and measured lateral deformation of facing wall .......... 89 Table 9 ...
... The current design for GRS Bridge is largely empirical-based and required validation for local materials and subsurface conditions and practice. This method addresses the advantages of closely-spaced geosynthetic reinforcement such as higher confinement, lower lateral deformation, suppress of dilation, and reduction in connection stress [44]. FHWA also calibrated the reliability of these models using performance test data, which have been correlated against results from laboratory and field monitoring programs [45]. ...
... Based on the test results of Pham (2009), Wu and Pham (2013) developed a Wfactor to account for the effect of reinforcement vertical spacing, which was used to develop a load-carrying capacity model for GRS composites. The FHWA published a very comprehensive study (Nicks et al., 2013) that involved a series of square GRS mini-pier tests using com- geotextiles of different tensile strengths and vertical spacing as reinforcement layers. Relatively large quantities of load tests (i.e., 19 tests) enabled the FHWA to establish a database of GRS material properties and evaluate the effects of reinforcement vertical spacing and tensile strength on the behavior of GRS structures. ...
... A parametric study was then conducted under both 2D and 3D conditions to investigate the influence of several key factors: reinforcement tensile stiffness, reinforcement vertical spacing, and a combination of reinforcement tensile stiffness and vertical spacing on the performance of GRS piers. Nicks et al. (2013) conducted 19 GRS mini-pier tests to investigate their axial load-deformation relationships. For each test, the GRS mass height-to-width ratio was kept at approximately 2.0 to minimize boundary effects. ...
... The numerical model included backfill soil, CMU blocks, concrete slab, geotextile layers, and different types of interfaces as shown in Fig. 1. A square GRS pier was adopted in the 3D numerical model with the same cross sectional area as that of the physical GRS pier used by Nicks et al. (2013). On the other hand, a slice of the GRS pier was adopted in the 2D numerical model with a unit width in the out-of-plane direction. ...
In this study, both two-dimensional (2D) and three-dimensional (3D) numerical analyses were carried out to evaluate the performance of geosynthetic-reinforced soil (GRS) piers. The numerical models were first calibrated and verified against test results available in the literature. A parametric study was then conducted under both 2D and 3D conditions to investigate the influences of reinforcement tensile stiffness, reinforcement vertical spacing, and a combination of reinforcement stiffness and spacing on the performance of GRS piers under vertical loading. Numerical results indicated that the effect of reinforcement spacing was more significant than that of reinforcement stiffness. The use of closely – spaced reinforcement layers resulted in higher global elastic modulus of the GRS pier, smaller lateral displacements of pier facing and volumetric change of the GRS pier, lower and more uniformly-distributed tension in the reinforcement, and larger normalized coefficients of lateral earth pressure. This study concluded that a 2D numerical model gave more conservative results than a 3D model.
... To properly design and maintain transportation infrastructure, it is necessary to monitor and understand the performance of the structure until its failure (Kermani 2013). Nicks et al. (2013) conducted 19 performance tests on GRS piers and investigated the effects of facing type and geotextile spacing and strength on the behavior of piers until failure. The test results showed that the frictionally-connected concrete masonry units (CMU) facing increased load bearing capacity and led to a stiffer response compared to a GRS pier with no facing blocks. ...
... The test results showed that the frictionally-connected concrete masonry units (CMU) facing increased load bearing capacity and led to a stiffer response compared to a GRS pier with no facing blocks. Nicks et al. (2013) concluded that the design assumption made by Adams et al. (2011) about excluding the effect of confinement from the facing in determining the capacity of GRS piers and abutments was conservative. Numerical studies have also been conducted to evaluate the behavior of GRS structures. ...
... In this study, the performance of GRS piers under axial loading until failure is investigated through a numerical investigation. A full-scale test of a GRS pier by Nicks et al. (2013) is simulated and the results are compared with the observed pier settlement data. The validated model is then used to conduct a parametric study to investigate the effects of reinforcement strength and spacing, pier height and its cross-sectional dimension on settlement within the GRS mass. ...
In this study, a numerical investigation was conducted to study the settlement of GRS piers under applied axial loads. A finite-difference program was used to model full-scale GRS piers. The backfill soil is simulated using the plastic hardening model combined with strain-softening behavior. The developed model is validated against the results of full-scale GRS pier performance tests. The numerical results were compared with the observed pier settlement data, and it was found that the model adequately captures the behavior of GRS piers under axial loading. After validation, the influences of reinforcement strength, reinforcement vertical spacing, pier height, and pier cross-sectional dimensions were investigated through a parametric study. Results indicated that increasing the reinforcement strength and decreasing its spacing have a significant benefit in reducing the settlement of GRS piers.
... The FHWA analytical method calculates ultimate bearing capacity based on the load-bearing capacity of soil-geosynthetic composite structures, and accounts for the maximum aggregate size and friction angle of the backfill soil and the vertical spacing and ultimate tensile strength of the geosynthetic reinforcement ( ). The allowable vertical stress for the service limit is then taken as 10% of the calculated ultimate bearing capacity ( Nicks et al. 2013Nicks et al. , 2016). The FHWA empirical method is based on a vertical stress-strain relationship that is measured from performance tests (e.g., GRS mini-pier loading tests) conducted using project-specific soil and geosynthetic materials ( Adams et al. 2011a, b). ...
... The FHWA empirical method is based on a vertical stress-strain relationship that is measured from performance tests (e.g., GRS mini-pier loading tests) conducted using project-specific soil and geosynthetic materials ( Adams et al. 2011a, b). In this case, the service limit is defined as an applied vertical stress of 200 kPa or the vertical stress at 0.5% vertical strain, and the strength limit is defined as the vertical stress at 5% vertical strain ( Berg et al. 2009;Adams et al. 2011a, b;Nicks et al. 2013). ...
... Field and laboratory loading tests have been conducted on largescale GRS piers and abutments and generally indicate satisfactory 1 performance under service loads and relatively high bearing capacity (Adams 1997;Gotteland et al. 1997;Ketchart and Wu 1997;Wu et al. 2001Wu et al. , 2006aAdams et al. 2011aAdams et al. , 2014Nicks et al. 2013Nicks et al. , 2016Iwamoto et al. 2015). Lee and Wu (2004) reviewed the results of several large-scale loading tests and suggested that bearing capacity can be as high as 900 kPa for closely spaced reinforcement and well-graded, well-compacted backfill soil. ...
This paper presents a numerical investigation of the deformation and failure behavior of geosynthetic reinforced soil (GRS) bridge abutments. The backfill soil was characterized using a nonlinear elastoplastic constitutive model that incorporates a hyperbolic stress-strain relationship with strain-softening behavior and theMohr-Coulomb failure criterion. The geogrid reinforcement was characterized using a hyperbolic load-strain-time model. The abutments were numerically constructed in stages, including soil compaction effects, and then monotonically loaded in stages to failure. Simulation results indicate that a nonlinear reinforcement model is needed to characterize deformation behavior for high applied stress conditions. A parametric study was conducted to investigate the effects of reinforcement, backfill soil, and abutment geometry on abutment deformation and failure behavior. Results indicate that reinforcement vertical spacing, reinforcement stiffness, backfill soil friction angle, and lower GRS wall height are the most significant parameters. The shape of the failure surface is controlled primarily by abutment geometry and can be approximated as bilinear.
... Experimental studies involving field and laboratory static loading tests have been conducted on large-scale GRS structures (Adams 1997;Gotteland et al. 1997;Ketchart and Wu 1997;Wu et al. 2001Wu et al. , 2006aAdams et al. 2011a;Nicks et al. 2013bNicks et al. , 2016. Results from these tests indicate that the GRS piers and abutments had satisfactory performance under design loads and relatively high load capacity. Lee and Wu (2004) reviewed several case studies of in-service GRS abutments (Won et al. 1996;Wu et al. 2001;Abu-Hejleh et al. 2002) and reported satisfactory performance under service load conditions. ...
... Experimental studies involving field and laboratory static loading tests have been conducted on large-scale GRS structures (Adams 1997;Gotteland et al. 1997;Ketchart and Wu 1997;Wu et al. 2001Wu et al. , 2006aAdams et al. 2011a;Nicks et al. 2013bNicks et al. , 2016. Results from these tests indicate that the GRS piers and abutments had satisfactory performance under design loads and relatively high load capacity. Lee and Wu (2004) reviewed several case studies of in-service GRS abutments (Won et al. 1996;Wu et al. 2001;Abu-Hejleh et al. 2002) and reported satisfactory performance under service load conditions. ...
... In contrast, values of settlement and abutment compression are nearly equal for all n br . The simulation results are consistent with observations from largescale loading tests on GRS minipiers, which indicate that bearing bed reinforcement can reduce lateral facing displacements but is unlikely to reduce settlement under typical design-level applied vertical stress conditions (≤200 kPa) (Nicks et al. 2013b). The effect of bearing bed reinforcement in Fig. 14(a) is less significant than results reported by Nicks et al. (2013b) because the bridge structure in the current study imposes horizontal friction forces on the bridge seat that act to reduce outward movement of the GRS abutment. ...
This paper presents numerical simulations of the performance of the Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) under static loading conditions. Simulations were conducted using a finite-difference program and realistic conditions for system geometry, backfill soil, geosynthetic reinforcement, and applied loads. Simulation results, including lateral facing displacements, settlements, lateral and vertical earth pressures, and reinforcement tensile strains and forces, indicate good performance of GRS-IBS during construction and under traffic loads. A parametric study was conducted to investigate the effects of backfill soil compaction, reinforcement length, reinforcement stiffness, bearing bed reinforcement, bridge seat setback distance, bridge load, and abutment height on the performance of GRS-IBS. Results indicate that reinforcement stiffness, bridge load, and abutment height have the most significant influences on lateral facing displacements and bridge seat settlements. Differential settlements between the bridge and approach roadway were small for all conditions.
... One problem is that these large scale PTs require specialized equipment and knowledge to perform. The method is atypical for most GRS bridges designed with different backfills and geosynthetics from what has already been tested (Adams et al., 2011a; Nicks et al., 2013); rather, a simple methodology is needed to estimate deformations without conducting mini-pier experiments. In addition, there are no guidelines to estimate the in-service reinforcement strain; however, for GRS, it is often assumed that the soil and the reinforcement strain together. ...
... In effect , compaction preloads the geosynthetic within the backfill, thus restraining lateral movement, locking-in internal stress and confinement to the soil, and strengthening the composite. Nicks et al. (2013) compared the results of an uncompacted and compacted GRS performance test. In these tests, the applied stress resulting in 0.5% vertical strain for the uncompacted sample was 15 kPa, whereas for the compacted sample with the same materials, the applied stress was 147 kPa, an increase in the load carrying capacity at the SLS by a factor of almost 10. ...
... The process was repeated until the mini-pier was completed (Figure 3a). For the tests with no facing (Figure 3b), the CMU blocks were removed after construction and the geotextile fabric was trimmed flush with the exposed GRS composite (Nicks et al., 2013). The series of tests were designed to examine the contributions of backfill type, reinforcement strength and spacing, and facing condition to the strength and serviceability of GRS composites, with deformations and strains the focus of this analysis. ...
... The experiments demonstrated that the soil-geosynthetic composites could be stabilized internally to form a very strong composite by closely spaced geosynthetic reinforcement. Fig. 3 A FHWA performance test specimen with facing blocks removed before load application [25] Tight Reinforcement Spacing Figure 4 shows distribution of vertical and lateral stresses in an unreinforced soil mass and a reinforced soil mass subjected to a vertical load (6.0 kN/m) on the top surface, as obtained from plane strain finite element analysis. The two soil masses have identical geometry and soil properties except that the reinforced soil mass contains three sheets of geosynthetic reinforcement, equally spaced at the top, mid-height, and bottom, on 0.3 m spacing. ...
... The high load-carrying capacity of GRS has been demonstrated in the Bperformance tests^(over 20 tests, 8 tests with facing blocks removed prior to testing) by the FHWA [25]. The test specimen with the facing blocks (used during preparation of the specimen) removed measures about 3.2 ft (length) × 3.2 ft (width) × 6.4 ft (height); see Fig. 3. ...
This article starts with an overview of reinforced soil retaining walls, in that the fundamental differences in design concepts between externally and internally stabilized reinforced soil walls were explained. Mechanically stabilized earth (MSE) walls belong to the former, whereas geosynthetic reinforced soil (GRS) walls belong to the latter. MSE walls with geosynthetics as reinforcement have sometimes been referred to as GMSE walls. GMSE walls have seen to suffer from an unusually high failure rate of about 5 to 8%. GRS walls, on the other hand, have seen a very low failure rate. This article addresses 11 major features of GRS which help to explain the very low failure rate. The features, learned from field-scale experiments and analytical studies, include the following: (1) behavior of internally stabilized reinforced soil mass, (2) effect of tight reinforcement spacing, (3) the lateral earth pressure (“bin pressure”) against facing, (4) facing connection strength of GRS, (5) relative roles of reinforcement spacing vs. reinforcement strength in GRS, (6) the Wu-Pham GRS load-carrying capacity equation, (7) approaching a K0 stress condition in GRS, (8) rational evaluation of pullout failure of GRS, (9) seismic resistance of GRS, (10) creep and stress relaxation of GRS, and (11) GRS with truncated base. It is the author’s hope that the article will add to reader’s understanding of GRS and make better use of this novel technology in wall construction.
... In recent years, awareness of the major advantages of installing sheet reinforcement with close spacing has grown. Close reinforcement spacing has considerable advantages that were initially seen during construction and afterward confirmed by several field-scale investigations [1,2,15,[25][26]34]. These tests have demonstrated that, in terms of a reinforced soil system's capability, reinforcement spacing is important considerably more than reinforcement strength. ...
When building Soil Geosynthetic Composite (SGC) walls, fill compaction is normally carried out by operating a compactor in a general direction parallel to the wall face. In other words, a moving point or area load is often used to apply a compaction load on a newly installed soil lift. Pham (2009) and Wu and Pham (2010) demonstrated that the compaction-induced stress (CIS) caused by multiple passes of a compactor moving toward or away from a section can be calculated by taking into account the compaction load applied directly above the section under consideration using a simplified stress path proposed by Duncan and Seed (1986). Additionally, by simulating the compaction, the CIS due to fill compaction may be correctly assessed. The CIS resulting from fill compaction can also be accurately assessed by simulating the compaction load, such as by applying a distribution load on top of each backfill layer or a distribution load at the top and bottom of each soil layer, or by applying various widths of strip load to the top of each backfill layer. The objective of this study was to validate the numerical simulation of the compaction load to stress deformation behavior of SGC mass under operating stress conditions. In order to conduct the numerical analysis, data from both a full-scale instrumented SGC mass based on large-scale soil geosynthetic composite (SGC) experiments and a 6 m-high SGC (Pham, 2009) were employed. This study will examine a few SGC behavior parameters, including reinforcement strains, lateral displacements, and reinforcement strains. The objective of the FE modeling is to demonstrate the effect, emphasize the significance of the compaction conditions to the stress-deformation behavior of SGC mass, and validate the findings from the field-scale experiments and proposed model by Pham (2009) and Wu and Pham (2010).
... The GRS abutment directly supports the bridge superstructure and is the most important component of the GRS-IBS. Research through field and laboratory loading tests show that GRS abutments have satisfactory performance under service load conditions and relatively large bearing capacity (Adams 1997;Ketchart and Wu 1997;Wu et al., 2001Wu et al., , 2006Nicks et al., 2013Nicks et al., , 2016Adams et al., 2014;Iwamoto et al., 2015;Xiao et al., 2016;Xu et al., 2019;Zheng et al., 2019;Doger and Hatami 2020;Hatami and Doger 2021). GRS-IBS structures involve complex interaction between the closely spaced geosynthetic reinforcement (i.e., vertical spacing ≤ 0.3 m) and well compacted backfill soil (Morsy et al., , 2020Morsy and Zornberg 2021). ...
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.
... He plotted the limited test data that was available at that time for soil reinforced with geosynthetics. The authors do not have those original plots, but his approach is recreated in Fig. 1 with more recent FHWA data (Nicks et al. 2013). ...
Professor Jonathan Wu’s career was devoted to rigorous development of internal stability in reinforced soil as a new and evolving technology. This paper presents two of Professor Wu’s students’ work on the search for internal stability by tracing his work. Engineering design of reinforced soil originated in France with Schlosser and Vidal in the late 1960s. The first designs were based on a simple limit state method. Analyzing test data, Schlosser later found that the limit method was insufficient and that internal stability involves stiffness. Wu found that stiffness was affected by reinforcement spacing. Settlement or collapse is shown in examples that violate this spacing criterion. Initial analysis and validation involved geosynthetic sheets, but these were extended to other materials and to strip reinforcement. The analysis has been validated both by laboratory data and by field observations. These findings corroborate those of international companies in the reinforced soil community, but they are often incompatible with code in North America. The studies and discussions presented in this paper are further enhanced with the most current testing and work to confirm Professor’s Wu insights and visions.
... The effect of surcharge has also been evaluated on the reinforced soil wall performance in several experimental and field work studies (e.g., Jewell and Milligan, 1993;Gomes et al., 1994;Palmeira and Gomes, 1996;Bathurst et al., 2000;Abu-Hejleh et al., 2002;Wu et al., 2006;Adams et al., 2011;Nicks et al., 2013;Lenart et al., 2016;Tatsuoka et al., 2016;Xiao et al., 2016;Mirmoradi and Ehrlich, 2017;Sabermahani et al., 2018) including numerical and analytical analyses (e.g., Helwany et al., 2003;Hatami and Bathurst, 2006;Ahmadi and Hajialilue-Bonab, 2012;Abu-Hejleh et al., 2014;Liu, 2015;Ambauen et al., 2016;Zheng et al., 2018). Nonetheless, the combined effect of the facing inclination and uniform surcharge has not yet been properly evaluated in the studies found in the literature. ...
In the current paper, using experimental studies and numerical analyses, the combined effect of facing inclination and uniform surcharge on the behaviour of geosynthetic-reinforced soil (GRS) walls under working stress conditions is evaluated. Data from four well-instrumented GRS walls at the end of construction and under surcharge applications were used considering different facing types, inclinations, and toe conditions. The numerical analyses were carried out considering different wall heights, facing inclinations, and surcharges. Moreover, data from the physical and numerical model studies were utilised to verify the predictability of the AASHTO simplified (2017) and Ehrlich and Mirmoradi (2016) design methods and some limitations of each method are discussed. The results clearly indicate that for better representation of the actual conditions, the uniform surcharge and facing inclination should not be independently taken into account in the design procedures.
... In Figure 1, the Wu-Pham instability is validated by capacity ratios for unfaced and faced soil structures tested at the US Federal Highway Administration (FHWA) [7]. ...
The 1/6 th Rule of Triaxial Testing says that particles larger than 1/6 th the diameter of the specimen will skew test results when not discarded. Although this rule is documented in the procedures of government laboratories, its origin is obscure. In this paper, the rule is derived as a corollary of granular stability. The stability derivation involves particle-continuum analysis. However, instead of a discrete element formulation or Cosserat mechanics, this paper uses the classical solution of Sokolovskii that is the modern basis of Terzaghi bearing capacity theory. Stability of a soil particle is addressed within the continuum by matching leading terms of series expansions, which is also known as the singular perturbation method. This finding is similar to previous derivations involving deformation of geosynthetic reinforced soil.
... The other differences between the two methods have been described in a number of publications (Nicks et al., 2013;Zornberg et al., 2014). The GRS-IBS design method is mainly focused on design of GRS abutment structures and it does not sufficiently cover design details of wing walls and walls supporting embankment (Zornberg et al 2014). ...
... The other differences between the two methods have been described in a number of publications (Nicks et al., 2013;Zornberg et al., 2014). The GRS-IBS design method is mainly focused on design of GRS abutment structures and it does not sufficiently cover design details of wing walls and walls supporting embankment (Zornberg et al 2014). ...
Geosynthetic reinforced soil (GRS) is a special soil with geosynthetic fabric closely stacked in
layers as soil stabilization and considered an alternative design method to the conventional bridge support
technology. In this research study, a field case study of Maree Michel bridge, which is located in
Route LA 91 Vermilion Parish in Louisiana, was instrumented with six different types of
instrumentations to monitor the performance of GRS-IBS bridge abutment and to develop 2D and
3D finite element models. The instrumentations include Shape Acceleration Array (SAA), earth
pressure cells, strain gauges, piezometers, and thermocouples. Additionally, surveying was
conducted at the bridge surface upon the completion of the construction. Two and threedimensional
finite elements (FE) computer program PLAXIS 2016 was chosen to model the GRS
abutment. First, the FE simulation is performed for the case study, in which the FE models were
verified using the results of field monitoring program. A comprehensive parametric study was then
conducted to evaluate the effect of different design variables on the performance of the GRS-IBS.
Based on the results of parametric study, the relationship between the reinforcement
spacing and the reinforcement strength on the behavior of the GRS-IBS performance was
evaluated. The results indicated that the reinforcement spacing has a higher impact than the
reinforcement strength on the performance of GRS-IBS for a reinforcement spacing equal or
greater than 0.2 m (8 in.), and similar impact for reinforcement spacing less than 0.2 m (8 in.). An
analytical model was developed to calculate the required tensile strength of GRS-IBS abutment
based on the composite behavior of the closely reinforcement soil. The equations were verified by
using field measurements and by the results of the finite element (FE) method of analysis. The
results of the analytical model were also compared with the current design procedure adopted by
the Federal Highway Administration (FHWA). Finally, the FE analysis demonstrated that the
vi
possible potential failure envelope of the GRS-IBS abutment was found to be a combination of a
punching shear failure at the top and Rankine failure surface at the bottom, in which the failure
envelope is developed under the inner edge of the footing and extending vertically downward to
intersect with the Rankine active failure surface.
... As geosynthetic reinforcements are used in a wide range of soil structures and these structures are subjected to various loading conditions including static and dynamic loads, more and more attention has been paid to evaluating the performance of geosynthetic-reinforced soil structures under static and dynamic loads by numerical calculations, laboratory and field tests, etc. For example, experimental studies involving field and laboratory static loading tests on geosynthetic-reinforced soil structures have been conducted [7][8][9][10][11]. Besides the response under static loads, there also have been many studies performed on the behaviors of geosynthetic-reinforced soil structures under dynamic loads. ...
... The significant beneficial effects of placing sheet reinforcement on small spacing, however, have gained increasing attention in recent years. The significant benefits of close reinforcement spacing were first realized in actual construction, and later validated by many field-scale experiments (1,3,7,12,19,21). These experiments have confirmed that reinforcement spacing plays a far greater role than reinforcement strength in the capacity of a reinforced soil system. ...
A study was undertaken to investigate stress-deformation behavior of soil-geosynthetic composites (SGC) by finite element method of analysis. Five field-scale experiments conducted on representative SGC of different reinforcement stiffness/strength and reinforcement spacing were used to validate the analytical model. An elasto-plastic soil model, referred to as the hardening soil model, was selected to simulate behavior of compacted fill in the SGC experiments. Model parameters were determined from results of large-size triaxial compression tests by following a set of procedure without back-calculation or calibration. Measured external and internal displacements, including vertical strains, horizontal displacement profiles, and internal movement at selected points of all five SGC tests, were found to be in very good agreement with simulation results from the analytical model up to an applied pressure of 1000 to 2000 kPa. The validated model therefore serves as a reliable tool for investigation of stress-deformation behavior of soil-geosynthetic composites. This paper presents validation of the analytical model, analysis of stresses and deformation of SGC, and influence of factors such as reinforcement stiffness, reinforcement spacing, soil stiffness and strength parameters on stress-deformation behavior of SGC. The study helps to gain improved understanding of stress-deformation behavior of soil-geosynthetic composites. © 2018 Springer Science+Business Media, LLC, part of Springer Nature
... The geosynthetically reinforced structures in the aforementioned studies had various reinforcement spacings from 15 to 60 cm. Basic design guidelines for GRS abutments are available that outline recommended soil type, gradation, and level of compaction of the backfill soils, along with the vertical spacing, strength, stiffness , and length of reinforcement layers (Adams et al. 2011b; Nicks et al. 2013). Although these design guidelines are reasonably well established, the prediction of GRS walls and abutment deformation under applied service loads requires further investigation. ...
Geosynthetic reinforced soil (GRS) walls and abutments are increasingly used to support transportation infrastructure. A pressing question in their response is the amount of horizontal deflection expected under service loads. This paper presents an evaluation of six methods for predicting the lateral deformation of GRS walls and abutments, namely the FHWA, Geoservice, CTI, Jewell-Milligan, Wu, and Adams methods. Field and laboratory performances of 17 GRS walls and abutments are compared with the predicted results from the six methods. A statistical analysis is then used to evaluate the conservativeness, accuracy, and reliability of these methods in predicting the maximum lateral deformation of GRS walls. The Adams method is the most accurate method for predicting the maximum lateral deformation if the amount of vertical deformation is reasonably known. Among the Geoservice, Jewell-Milligan, and Wu methods, which have the ability to predict the lateral deformation of GRS walls at various elevations where reinforcements are located, the Wu method is the most accurate and reliable method for predicting the lateral deformation of GRS walls.
... Eleven GRS load tests performed at FHWA's TFHRC (designated as "TF " ) with and without cast masonry unit or CMU facing that was frictionally connected to the geosynthetic are reported in [20] Notes: Each CMU block was 0.194-m-high x 0.397-m-long x 0.194-m-wide (Fig. 4a).A schematic of tests TF-1, 2, 6, 9 and 12, each 10 blocks high, is shown in Figs. 4b, 4c, 5a, and 5b. ...
... Therefore, the column PT is fairly representative of an in-service PS condition for well-graded gravels in this case. [20] Notes: ...
A database of load tests performed on geosynthetic reinforced soil (GRS - reinforcement in this study is of the extensible variety) was developed using results of recent load tests performed on large scale GRS structures at the Federal Highway Administration's Turner Fairbank Highway Research Center as well as results from the literature. The measured capacities were compared to those predicted using the Wu and Pham [1] equation utilizing both the peak and fully softened soil shear strength parameters. It was found that the fully softened strengths yielded capacities that agreed better with the measured capacities. A rationale for this finding is that the robust reinforcement in a GRS strengthens the soil considerably causing the GRS to experience large strains prior to failure. Because the soil peak strengths are mobilized at relatively small displacements/strains even in large scale direct shear or triaxial tests compared to the GRS load tests, it is postulated that the fully softened values are more appropriate to estimate the GRS bearing capacity. A follow-on to this is that since large movements are required to fail say a GRS abutment, the design of GRS abutments will most likely be governed by the serviceability limit state rather than the ultimate limit state.
... Recently, an extensive series of load tests on GRS/GMSE mini-piers or soil columns were performed at FHWA's Turner-Fairbank Highway Research Center (TFHRC) with and without concrete masonry unit (CMU) facing frictionally connected to the reinforcement ( Nicks et al. 2013). The tests with facing were instrumented with vertical and lateral pressure cells that provide valuable information to meet the following objectives: ...
Four pairs of large-scale instrumented geosynthetic reinforced soil (GRS) square columnswere load tested to study the effects of varying reinforcement strength to spacing ratio, to discern the lateral pressures during construction and during load testing, and to derive shear strength parameters of the GRS composite. Each pair was identical in every respect, except onewas loaded with a dry-stacked concrete masonry unit (CMU) facing in place and the other without. Lateral pressures during constructionwere found to be small for the facing type used in this study. Also, based on the derived GRS composite shear strength parameters, it was found that (1) the GRS composite Mohr-Coulomb envelopes are not parallel to those for the unreinforced soil; (2) the reinforcement increased the composite cohesion compared to the unreinforced soil (cohesion increases with decreasing spacing and increasing reinforcement strength); (3) the composite friction angle is less than that of the unreinforced soil (friction angle increases with decreasing reinforcement strength and increasing spacing); (4) as the composite friction angle increases, the active lateral earth pressure coefficient decreases; and (5) the benefits of reinforcing a soil become increasingly significant as the reinforcement spacing decreases.
... The behavior of geosynthetic reinforced soil mass has been the subject of many studies. The significant benefit of small reinforcement spacing (on the order of 0.1 to 0.3 m) for increased stiffness and strength of a reinforced soil mass has been investigated analytically by Wu and Pham [17] and verified by many full-scale experiments (e.g., [3,8,10,12,16]) as well as hundreds of walls in actual construction [4,5]. The ultimate load-carrying capacity of a reinforced soil mass has been found to be well over 1,000 kPa with medium strength geosynthetic reinforcement at 0.2-m spacing and a well-compacted granular backfill. ...
There have been ongoing arguments whether heavy blocks and/or facing connection enhancement elements, such as pins, lips, or keys, are needed for facing stability of segmental reinforced soil walls with geosynthetic reinforcement. This study was undertaken to examine facing connection forces for vertical or near vertical segmental reinforced soil walls with purely friction connections. In the study, the lateral earth pressure was assumed to be the Rankine active earth pressure—an assumption that has been employed by most current design methods of reinforced soil walls with extensible reinforcement. Based on force equilibrium, the driving forces and resisting forces at facing connections are derived for situations where reinforcement is at every course of facing blocks and at every three courses of facing blocks. For the latter, both the connection forces at geosynthetic–block interface and at block–block interface are considered. Based on these connection force equations, generalized equations of driving and resisting forces for any number courses of blocks between adjacent reinforcement layers are developed. Using the generalized connection force equations, comparisons of driving and resisting forces for some common parameter values and under typical conditions of reinforced soil walls were performed. The significance of reinforcement spacing, as well as the need, or lack thereof, for heavy facing blocks and/or additional connection measures on facing stability is discussed. The benefit of small reinforcement spacing is demonstrated. A common perception that a higher wall is more susceptible to connection failure is true only for segmental walls with larger reinforcement spacing.
O emprego de encontros de ponte ou de viaduto a partir de solo reforçado com geossintético (SRG) como suporte direto do tabuleiro vem sendo cada vez mais adotado, tendo em vista vantagens significativas em relação aos sistemas convencionais. Este estudo tem como objetivo analisar o efeito do espaçamento vertical reduzido no desempenho de um maciço de SRG com face em blocos, sujeito a uma sobrecarga uniformemente distribuída. Para as análises paramétricas, foi utilizado o software de elementos finitos Plaxis 2D, considerando diferentes condições de espaçamento vertical (Sv) e rigidez do reforço (J) mantendo J/Sv constante. Os resultados indicaram um efeito significativo do espaçamento vertical. Com o emprego de menores valores de Sv, observou-se uma diminuição dos deslocamentos laterais máximos do faceamento e dos recalques do solo de aterro na face. Nas massas de SRG que se empregaram espaçamento vertical reduzido e reforços menos rígidos apresentaram maior restrição à movimentação vertical do solo de aterro próximo à face e menores deformações horizontais e verticais quando comparado aos maciços que se adotaram maior espaçamento vertical e reforços mais rígidos. Esse mesmo comportamento foi obtido para as diferentes razões J/Sv.
Five centrifuge models of geosynthetic reinforced soil (GRS) abutments with segmental block facing were loaded in acceleration field under plane strain condition. Influences 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 while decreased due to a larger bearing area. The rupture of reinforcements was observed and considered as the cause of the failures. Comparing with the measured ultimate bearing capacity, the values calculated by the semi-empirical formula of design guideline were significantly conservative. The failure surface of failed abutment developed from 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 were provided.
This paper presents two-dimensional (2D) and three-dimensional (3D) numerical simulations of a half-scale geosynthetic reinforced soil (GRS) bridge abutment during construction and bridge load application. The backfill soil was characterized using a nonlinear elastoplastic model that incorporates a hyperbolic stress–strain relationship and the Mohr–Coulomb failure criterion. Geogrid reinforcements were characterized using linearly elastic elements with orthotropic behavior. Various interfaces were included to simulate the interaction between the abutment components. Results from the 2D and 3D simulations were compared with physical model test measurements from the longitudinal and transverse sections of a GRS bridge abutment. Facing displacements and bridge seat settlements for the 2D and 3D simulations agree well with measured values, with the 2D-simulated values larger than the 3D-simulated values due to boundary condition effects. Results from the 3D simulation are in reasonable agreement with measurements from the longitudinal and transverse sections. The 2D simulation can also reasonably capture the static response of GRS bridge abutments and is generally more conservative than the 3D simulation.
In the current paper, using experimental studies and numerical analyses, the effect of surcharge width on the behavior of geosynthetic-reinforced soil (GRS) walls is evaluated under working stress conditions. Experimental tests were performed at a facility at the Geotechnical Laboratory of COPPE/UFRJ, using block and wrapped-face walls. Four well-instrumented GRS walls were examined considering different facing type and surcharge width. The numerical analysis of GRS walls was carried out using the two-dimensional computer program PLAXIS. Parametric studies were carried out with different combinations of surcharge width, wall height, compaction induced stresses (CIS) and face inclination. The results indicate the effect of the surcharge width in combination with other investigated factors on the magnitude and the position of the maximum reinforcement load and the lateral facing displacement of GRS walls.
In this study, three-dimensional numerical analyses were carried out to investigate the effects of reinforcement pullout resistance including facing connection strength on the behavior of geosynthetic-reinforced soil (GRS) piers under a service load condition. Three different piers were investigated in this study, which simulated different levels of reinforcement pullout resistance. Each pier had two cases with different reinforcement stiffness J and reinforcement spacing Sv but the same ratio of J/Sv. Numerical results showed that reinforcement pullout resistance had a significant effect on the behavior of GRS piers. When the pullout mode prevailed, the case with small Sv and low J had smaller lateral facing displacements and vertical strain of the pier under the same applied pressure as compared to the case with large Sv and high J when the ratio of J/Sv was kept constant. When the pullout mode did not prevail, two cases with the same ratio of J/Sv showed similar performance despite different combinations of Sv and J were used. To more effectively mobilize reinforcement strength and improve GRS pier performance, small reinforcement spacing or high-strength facing connection should be considered when sufficient reinforcement pullout resistance cannot be guaranteed otherwise.
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.
The fundamental design concept for an internally stabilized reinforced walls is quite different from that of externally stabilized reinforced walls. The backfill in internally stabilized reinforced walls is “reinforced” by geosynthetic inclusion in such a way that the soil‐geosynthetic composite needs to be sufficiently stable under its self‐weight and upon load applications. Internally stabilized soil walls rely on soil‐reinforcement interaction to generate different reinforcing mechanisms to achieve a stable system. This chapter focuses on internally stabilized walls. It discusses the theory of reinforced soil in general and geosynthetic reinforced soil (GRS). The chapter also discusses various reinforcing mechanisms of internally stabilized soil walls. It describes some common types of GRS walls. GRS refers to a reinforced soil mass with geosynthetic inclusion on tight vertical spacing. The chapter then discusses three sets of experiments conducted to investigate the load‐deformation behavior of GRS with closely spaced reinforcement.
A 109.5-Ft-long Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) in Hawaii was instrumented to measure superstructure strains, vertical pressures below the footing, lateral pressures behind the end wall and modular block facing, and lateral displacements of the facing. Field surveys were also performed to measure the bridge footing settlement. The field data showed that: (1) with time the superstructure compressive concrete strains gradually increased and the end wall lateral pressures gradually decreased, evidence of superstructure concrete creep and shrinkage; (2) three years after construction, the total footing settlement was ≈ 1.2 in.; and (3) the bridge superstructure undergoes daily and seasonal thermal expansion and contraction cycles. Also seasonally, the vertical pressures beneath the footing, lateral pressures behind the end walls, and superstructure strains fluctuate cyclically. The vertical footing pressure closest to the stream experienced the greatest daily pressure fluctuation (≈ 2500−3000 psf), while the one nearest the end wall experienced the least. Based on the results of cyclic triaxial tests on a basalt aggregate similar to the GRS backfill to estimate permanent deformation of the abutment due to daily pressure fluctuations, it was estimated that the permanent strain ≈ 1%, comparable to what was observed in the bridge footing. After three years, the total settlement is about 1.6% of the GRS abutment height; ≈ 0.7% of this is due to the structure dead weight and the remaining 0.9% is due to cyclic loading, consistent with the 1% cyclic strain from laboratory permanent deformation tests. © National Academy of Sciences: Transportation Research Board 2019.
This paper presents an experimental study on the response of a half-scale geosynthetic reinforced soil (GRS) bridge abutment subjected to shaking in the direction transverse to the bridge beam. The specimen geometry, reinforcement stiffness, soil modulus, applied surcharge stress and characteristics of the earthquake motions were scaled according to established similitude relationships for shaking table tests in a 1g gravitational field. The GRS bridge abutment was constructed using modular facing blocks, well-graded angular sand and uniaxial geogrid reinforcement, in both the longitudinal and transverse directions. Facing displacements, bridge seat settlements, accelerations, vertical and lateral soil stresses, reinforcement strains, and bridge seat and bridge beam interactions were measured during a series of input motions. The average incremental residual bridge seat settlement was 4.7 mm after the Northridge motion, which corresponds to a vertical strain of 0.22% for the lower GRS fill. After the series of motions, the maximum residual tensile strains occurred near the facing block connections for the lowermost reinforcement layer and under the bridge seat for higher reinforcement layers.
This paper presents a numerical investigation of the deformation response of geosynthetic reinforced soil (GRS) mini-piers under service load conditions. The backfill soil was characterized using a nonlinear elasto-plastic constitutive model that incorporates a hyperbolic stress-strain relationship and the Mohr-Coulomb failure criterion. The geotextile reinforcement was characterized using linearly elastic elements with orthotropic stiffness. Various interfaces were included to simulate the interaction between different components. The three-dimensional numerical model was validated using experimental data from GRS mini-pier loading tests, including average settlements and maximum lateral facing displacements. Simulation results from a parametric study indicate that backfill soil friction angle, backfill soil cohesion, reinforcement vertical spacing, and reinforcement stiffness have the most significant effects on settlements and lateral facing displacements for GRS mini-piers under service load conditions.
This paper presents an experimental study on the dynamic response of a half-scale geosynthetic-reinforced soil (GRS) bridge abutment system using a shaking table. Experimental design of the model specimen followed established similitude relationships for shaking table tests on reduced-scale models in a 1-g gravitational field, including scaling of model geometry, geosynthetic-reinforcement stiffness, backfill soil modulus, bridge load, and characteristics of the earthquake motions. The 2.7-m-high GRS bridge abutment was constructed using well-graded sand backfill, modular facing blocks, and uniaxial geogrid reinforcements with a vertical spacing of 0.15 m in both the longitudinal and transverse directions. A bridge beam was placed on the GRS bridge abutment at one end and on a concrete support wall resting on a sliding platform off the shaking table at the other end. The GRS bridge abutment system was subjected to a series of input motions in the longitudinal direction. Results indicate that the testing system performed well, and that the GRS bridge abutment experienced small deformations. For two earthquake motions, the maximum incremental residual facing displacement in model scale was 1.0 mm, and the average incremental residual bridge seat settlement in model scale was 1.4 mm, which corresponds to a vertical strain of 0.7 %.
This paper presents an experimental study on the seismic performance of a half-scale geosynthetic-reinforced soil (GRS) bridge abutment. Experimental design of the scale model followed established similitude relationships for shaking table testing in a 1 g gravitational field. This involved scaling of model geometry, reinforcement and backfill stiffness, bridge load, and characteristics of the earthquake motions. The GRS abutment was constructed using well-graded sand, modular facing blocks, and uniaxial geogrid reinforcements with a vertical spacing of 0.15 m in both the longitudinal and transverse directions. The bridge deck was placed on the GRS abutment at one end and supported by a concrete wall resting on a sliding platform off the shaking table at the other end. The table was connected to the base of the support wall with steel beams to transmit the table motions. The measured lateral facing displacements and bridge seat settlements during application of a series of earthquake motions in the longitudinal direction are presented and indicate good seismic performance of the GRS bridge abutment.
The Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) is a
composite bridge structure built using GRS abutments and prefabricated bridge superstructure
elements. This accelerated bridge construction technology has been developed and promoted by
researchers and engineers from the United States of America’s Federal Highway Administration
(FHWA). GRS-IBS technology has proven itself useful for rapid, cost-effective bridge
construction in other regions of the United States. Consequently, the Delaware Department of
Transportation (DelDOT) constructed the first GRS-IBS in the state of Delaware (Br. 1-366) in
2013 to explore the effectiveness of this technology for use within their own bridge inventory.
This report provides an overview of the design, construction, and monitoring process
that was utilized to deploy the first constructed GRS-IBS in Delaware. Recorded performance
data for the structure from the time of construction, live load testing, and over three years of inservice
operation were collected using different types of instruments and analyzed.
Details regarding GRS-IBS technology, Br. 1-366 project requirements, the design
and construction procedure, and the instrumentation system that was utilized for monitoring the
health of the structure have been presented in Chapters 1 through 3.
The collected engineering data from different phases of the project are presented in
Chapter 4, including construction, live load testing, and over three years of in-service operation.
Since the amount of collected data was quite large, some techniques were utilized to
manage and filter the recorded data, as described in Chapter 5. A technique for statistical
correlation analysis is also presented in this chapter, which was found to be very useful for
xxv
developing an understanding of interrelationships between various sensor measured values. The
correlation between different types of readings are investigated using this technique, and the
corresponding findings from this analysis are presented in this chapter.
A strong effect of temperature on the measured strain readings was observed, as
discussed in Chapter 5. Chapter 6 presents a correction procedure to account for the effects of
temperature on the measured strain values. The use of this correction technique allows for
significant refinement of the measured strain values within the GRS abutment.
The details and findings from a robust live load testing program are presented in
Chapter 7. More specifically, the effect of the live load on the strain in the abutments and the
pressure within and beneath the abutments have been investigated in this chapter. It is shown that
the structure was quite stable during each of the live load test events, with the induced pressure
and deformation by the live loads being quite low, and with little corresponding strain being
measured within the GRS abutments.
The applied pressure distribution beneath the west GRS abutment foundation was
investigated during construction and live load testing, as described in Chapter 8. It is shown that
the pressure distribution is not uniform and the maximum pressure is measured beneath the facing
wall. An approach is suggested in this chapter to predict the applied pressure induced by the
abutment and the surcharge loads.
The long term performance of the structure is analyzed in Chapter 9 using the data
collected by different sensors over three years of in-service operation. The data analysis shows the
effect of the precipitation amount and type (rain and snow) on the abutment water content. The
abutment performance that occurs as a result of changes in water content appears satisfactory.
Creep deformation did occur in the abutment, but its overall magnitude was quite small over the
xxvi
monitoring period, with the maximum strain being less than 0.5%. The lateral deflection and
settlement of the facing walls was small, less than 12 mm. The concrete bridge deformation was
also small, with the measured results being affected by the air temperature change. The abutment
temperature distribution was different in hot and cold weather. The clay foundation beneath the
abutment experienced some minor creep deformation. The results also indicated the effect of
temperature on the measured foundation and abutment pressure.
Finally, the overall conclusions of this report are presented in Chapter 10 and some
recommendations are made for future research.
This 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 spacing, and bridge load have the most significant influence on lateral facing displacements and bridge footing settlements for GRS abutments. Differential settlements between the bridge footing and approach roadway were small for all simulated conditions.
Reinforced soil composites and mechanically stabilized earth (MSE) walls are frequently employed to carry large surcharge or footing loads. For the safety and serviceability of these reinforced soil structures, it is necessary to analyze the reinforcement load and compression of reinforced soil mass subjected to surcharge loading. In the research reported in this paper, an analytical method proposed by the writer was extended to meet these needs. The extended analytical method explicitly considers soil nonlinearity, soil dilatancy, soil-reinforcement interaction, and end restrictions of reinforced soil mass. Both plane-strain and triaxial stress states can be considered in the method. The applicability of the method for reinforcement load was validated against eight large-scale tests of reinforced soil mass or MSE walls, and the method for reinforced soil compression was validated against two large-scale tests. The compressions of four reinforced soil minipiers under surcharge loading were also predicted. The proposed method has the capacity to unify the analyses of reinforcement load and compression of a reinforced soil mass under low to medium surcharge loading. Some issues in the application of the proposed method are also discussed. (C) 2015 American Society of Civil Engineers.
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.
Four geosynthetic-reinforced soil (GRS) piers, each built with different reinforcement strengths and aggregate backfill material, were constructed at the FHWA's Turner-Fairbank Highway Research Center in collaboration with the Long-Term Bridge Performance Program. The objective of the research is to assess the secondary deformation characteristics of GRS for load-bearing applications under service load conditions. The experiment consisted of axially loading the piers with 490 kN decommissioned prestressed concrete girders, resulting in an equivalent vertical applied stress of 200 kPa. The geometry of each GRS composite was 1.2 m square by 2.3 m in height, for an approximate base to height ratio of 0.5. The facing element for each GRS pier is a simple, split-faced concrete masonry unit (CMU) that is frictionally connected to the GRS composite at a nominal vertical reinforcement spacing of 0.2 m. The piers were instrumented to record reinforcement strain, earth pressures, and deformations. This paper will discuss the objectives of the experiment, explain the testing program, and share some of the vertical deformation results after almost four months in service. In addition, the results will be compared with the results of a long-term (since 1999) study on secondary settlement of a GRS abutment.
A study was undertaken to investigate the behavior of Geosynthetic Reinforced Soil (GRS) masses under various loading
conditions and to develop a simplified analytical model for predicting deformation characteristics of a generic GRS mass.
Significant emphasis was placed on the effect of preloading. To conduct the study, a revised laboratory test, known as the
Soil-Geosynthetic Performance (SGP) test, was first developed. The test is capable of investigating the behavior of a
generic GRS mass in a manner mimicking the field placement condition, and the soil and geosynthetic reinforcement are
allowed to deform in an interactive manner. A series of SGP tests was performed. Different soils and reinforcements were
employed, and the soil-geosynthetic composites were subject to various loading sequences. The tests showed that
preloading typically reduces vertical and lateral deformations of a generic soil mass by a factor 2 to 7, and that prestressing
(preloading followed by reloading from a non-zero stress level) can further increase the vertical stiffness by a factor of 2 to
2.5. Correlations between the results of SGP tests and full-scale GRS structures were evaluated. It was found that the
degree of reduction in settlement due to preloading could be assessed by the SGP test with very good accuracy. Finite
element analyses were performed to examine the stress distribution in the SGP test. The importance of using small
reinforcement spacing was evidenced by the stress distribution. A Simplified Preloading-Reloading (SPR) analytical model
was developed to predict the deformation characteristics of a GRS mass subject to monotonic loading and
preloading/reloading. The SPR model was shown to be able to accurately predict the results obtained from the SPG tests
and numerical analysis of automated plane strain reinforcement (APSR) tests.
Geosynthetic-Reinforced Soil (GRS) mass, comprising soil and layers of geosynthetic reinforcement, is not a uniform mass. To examine the behavior of a GRS mass by a laboratory test, a sufficiently large-size specimen of soil and reinforcement is needed to produce a representative soil-geosynthetic composite. This paper presents a generic test, referred to as the Soil-Geosynthetic Composite (SGC) test, for investigating stress-deformation behavior of soil-geosynthetic composites in a plane strain condition. The specimen dimensions, 2.0 m high and 1.4 m wide in a plane strain configuration, were determined by the finite element method of analysis. The configuration, specimen dimensions, test conditions, and procedure of the SGC test are described. In addition, the results of a SGC test with nine sheets of reinforcement, as well as those of an unreinforced soil test conducted in otherwise identical conditions, are presented. In the test, the soil mass was subject to a prescribed value of confining pressure, applied by vacuum through latex membrane covering the entire surface area of the mass in an air-tight condition. Vertical loads were applied on the top surface of the soil mass until a failure condition was reached. The behaviors of the soil masses, including vertical displacements, lateral movement, and strains in the geosynthetic reinforcement, were carefully monitored. The measured data allow the behavior of reinforced and unreinforced soils to be compared directly, provide a better understanding of soil-geosynthetic composite behavior, and serve as the basis for verification of numerical models to investigate the performance of GRS structures. J. Ross Publishing, Inc.
In current design methods for reinforced soil walls, it has been tacitly assumed that reinforcement strength and reinforcement spacing play an equal role. This fundamental design assumption has led to the use of larger reinforcement spacing (0.3-1.0 m) in conjunction with stronger reinforcement to reduce construction time. Recent studies, however, have clearly indicated that the role of reinforcement spacing is much more significant than that of reinforcement strength. With closely spaced (reinforcement spacing <= 0.3 m) reinforcement, the beneficial effects of geosynthetic inclusion is significantly enhanced, and the load-deformation behavior can be characterized as that of a composite material. A reinforced soil mass with closely spaced geosynthetic reinforcement is referred to as geosynthetic-reinforced soil (GRS). In this study, an analytical model is developed for predicting the ultimate load-carrying capacity and required reinforcement strength of a GRS mass. The model was developed based on a semiempirical equation that reflects the relative roles of reinforcement spacing and reinforcement strength in a GRS mass. Using measured data from field-scale experiments available to date, it is shown that the analytical model is capable of predicting the ultimate load-carrying capacity and required reinforcement strength of a GRS mass with good accuracy. (C) 2013 American Society of Civil Engineers.
The design and construction of retaining walls is an important aspect of geotechnical engineering practice in the development and maintenance of the world's civil infrastructure. A broad variety of design and construction methods are currently available to designers and contractors. Guidelines and standards exist for most of the design methods currently employed around the world. However, geotextile 1 reinforced soil composite (GRSC) walls, which use ancient, robust and proven design and construction techniques, are currently not covered by any widely known or accepted design and construction guideline or standard. When referring to this type of design as GRS, some professionals, researchers and government agencies consider it to be a simple subset of the widely accepted mechanically stabilized earth (MSE) design and construction technique. However, there are many fundamental engineering differences between MSE and GRSC including recognition of: compaction-induced stresses (CIS); geotextile-soil interaction; reinforcement spacing versus aggregate particle size; stresses and strains in the reinforcement; creep behaviour; and quality assurance / quality control (QA/QC). Full-scale test comparisons of MSE and GRSC walls have demonstrated the fundamental design and performance differences between these two technologies. When using an MSE design approach for GRSC walls, the beneficial effects of the geotextile can be underestimated and the soil loading imposed on the geotextile can be overestimated. The use of MSE design standards for GRSC walls is not supported by the current state of knowledge of soil-geotextile composite behaviour. In addition, the MSE design standards encourage the use of wide spacing between reinforcement layers. This financially favours the use of strong, uniaxial grid type reinforcement; increases the complexity of the designs; and increases the difficulty of project QA/QC. In other words, MSE wall design standards do not support or acknowledge composite behaviour and as such their application to GRSC wall design is fundamentally unsound. A simple, independent standard for GRSC wall design and construction is required to encourage the re-emergence of this economical, robust and proven technology. 1 The term geotextile refers to the use of textiles in geotechnical applications. J.P. Giroud has been credited for the development of the term geotextile.
Reliability-based design concepts and their application to load and resistance factor design (LRFD or limit states design (LSD) in Canada) are well known, and their adoption in geotechnical engineering design is now recommended for many soilstructure interaction problems. Two important challenges for acceptance of LRFD for the design of reinforced soil walls are (i) a proper understanding of the calibration methods used to arrive at load and resistance factors, and (ii)the proper interpretation of the data required to carry out this process. This paper presents LRFD calibration principles and traces the steps required to arrive at load and resistance factors using closed-form solutions for one typical limit state, namely pullout of steel reinforcement elements in the anchorage zone of a reinforced soil wall. A unique feature of this paper is that measured load and resistance values from a database of case histories are used to develop the statistical parameters in the examples. The paper also addresses issues related to the influence of outliers in the datasets and possible dependencies between variables that can have an important influence on the results of calibration.
The influence of a variation with depth of Young's modulus on the stresses and displacements in an isotropic elastic half-space, subject to loading normal to its plane boundary, is considered. The case of an incompressible medium with a modulus E(z) increasing linearly with depth is examined in some detail. It is shown that if £(0) =0 the loaded surface settles an amount w0 proportional to the local intensity q of applied pressure : where the factor ks (the coefficient of subgrade reaction) is independent of the size or shape of the loaded area and equal numerically to twice the rate of increase of E with depth. Outside the loaded area the surface does not settle. These results provide an interpretation of the coefficient of sub-grade reaction in terms of the mechanical behaviour of a non-homogeneous elastic continuum. Furthermore, in this special case the components of stress are shown to be unaffected by the depth variation of E.
Bridge abutments made of geotextile-reinforced soil have been shown to support the bridge load without the use of piles. However, current design procedures are considered to be conservative. To determine the strength, and to understand better the behavior of reinforced soil, large unconfined cylindrical soil samples reinforced with geosynthetics were axisymmetrically loaded. Samples were 2.5 ft (0.76 m) in diameter and 5 ft (1.52 m) in height. Peak strengths of 4.8 kips/ft 2 (230 kPa) to 9.6 kips/ft 2 (460 kPa) at 3% to 8.5% vertical strain were obtained from cylinders reinforced with geotextiles at 6-in. (152-mm) vertical spacing. A strength reduction occurred after the peak strength, but most of the loads were sustained up to at least 10% strain before yielding. Tension in the reinforcement appears to be mobilized first in the middle layers, as determined from the location of tears in the geotextile. An equation to calculate the tensile force in the reinforcement, T max, in a reinforced bridge abutment is proposed. The normalized strains led to the development of the strain distribution factor incorporated in the proposed equation. The proposed equation is slightly more conservative or almost equal, depending on the type of facing, when compared with the K o-stiffness method, but gives values approximately one-half of those obtained using the National Concrete Masonry Association and FHWA Demonstration Project 82 methods.
The ultimate uplift capacity of foundations with special reference to transmission tower footings is evaluated. A number of model uplift tests made by the authors and by others were studied and compared with full-scale tests. These tests showed a complex failure mechanism which varied with the depth of the foundation. Using simplifying assumptions a general theory was produced. It was shown that with suitable modification for shape and depth a useful relationship was available for computing the full-scale uplift capacity of foundations. It was further shown by model tests that the theory could be modified to take into account group action. Further research is required to evaluate the effect of combined loads and long-term effects.
The paper summarizes the calibration procedure used to calculate load and resistance factors for the Ontario Bridge Design Code 1983 edition. The limit states considered include serviceability and ultimate limit states during service and in construction. The acceptance criterion is closeness to a predetermined target safety level. Safety is measured in terms of a reliability index. The results of calibration are discussed for composite steel–concrete girders, pretensioned concrete girders, post-tensioned concrete decks, and timber decks. The analysis of construction design criteria is demonstrated on segmental bridges. Key words: code calibration, bridges, reliability index, load and resistance factors, limit states.
Results of both triaxial and direct shear tests on reinforced soil samples performed by different investigators have shown that soil dilatancy and extensibility of the reinforcements have a significant effect on the generated tension forces in the inclusions. An appropriate soil--reinforcement load transfer model, integrating the effect of soil dilatancy and reinforcement extensibility is therefore needed to adequately predict forces in the inclusions under expected working loads. This paper present a load transfer model assuming an elastoplastic strain hardening behaviour for the soil and an elastic--perfectly plastic behaviour for the reinforcement. This model is used to analyse the response of the reinforced soil material under triaxial compression loading. A companion paper present the application of this model for numerical simulations of direct shear tests on sand samples reinforced with different types of tension resisting reinforcements. The model allows an evaluation of the effect of various parameters such as mechanical characteristics and dilatancy properties of the soil, extensibility of the reinforcements, and their inclination with respect to the failure surface, on the development of resisting tensile stresses in the reinforcements. A parametric study is conducted to evaluate the effect of these parameters on the behaviour of the reinforced soil material. An attempt is also made to verify the proposed model by comparing numerical predictions with available experimental results of both triaxial and direct shear tests on reinforced soil samples. This model can be used for analysis and design of reinforced soil walls with different types of tension resisting inclusions to predict tension forces under expected working loads.
Geosynthetic Reinforced Soil Integrated Bridge System Synthesis Report
- M Adams
- J Nicks
- T Stabile
- J Wu
- W Schlatter
- J Hartmann
Adams, M., Nicks, J., Stabile, T., Wu, J., Schlatter, W., and Hartmann, J., "Geosynthetic
Reinforced Soil Integrated Bridge System Synthesis Report," Report, FHWA-HRT-11-027,
Federal Highway Administration, McLean, VA, 2011b.
Vegas Mini Pier Experiment and Postulate of Zero Volume Change
- M T Adams
- C P Lillis
- J T H Wu
- K Ketchart
Adams, M.T., Lillis, C.P., Wu, J.T.H., and Ketchart, K., "Vegas Mini Pier Experiment and
Postulate of Zero Volume Change," Proceedings, Seventh International Conference on
Geosynthetics, Nice, France, 2002, pp. 389-394.
Mini Pier Experiments: Geosynthetic Reinforcement Spacing and Strength as Related to Performance
- M T Adams
- K Ketchart
- J T H Wu
Adams, M.T., Ketchart, K., and Wu, J.T.H., "Mini Pier Experiments: Geosynthetic
Reinforcement Spacing and Strength as Related to Performance," Geotechnical Special
Publication 165, Geosynthetics in Reinforcement and Hydraulic Applications, Geo-Denver
2007, ASCE, Denver, CO, 2007.
American Association of State Highway and Transportation Officials
AASHTO, "LRFD Bridge Design Specifications, Edition 5," Report, American Association
of State Highway and Transportation Officials, Washington, DC, 2012.
Composite Behavior of Geosynthetic-Reinforced Soil (GRS) Mass
- J T H Wu
- T Q Pham
Wu, J.T.H., Pham, T.Q., and Adams, M.T., "Composite Behavior of Geosynthetic-Reinforced Soil (GRS) Mass," Report, FHWA-HRT-10-077, Federal Highway
Administration, McLean, VA, 2010.
Geotex Woven Geotextiles Product Information
- Propex
Propex, "Geotex Woven Geotextiles Product Information,"
<http://geotextile.com/product/geotex.html>, retrieved on December 6, 2012.
US 3600/3600 Product Information
- Us Fabrics
US Fabrics, "US 3600/3600 Product Information,"
<http://www.usfabricsinc.com/products/us-3600-3600>, retrieved on December 6, 2012.
GRS Bridge Piers and Abutments
- J T J Wu
- K Ketchart
- M Adams
Wu, J.T.J., Ketchart, K., and Adams, M. "GRS Bridge Piers and Abutments," FHWA
Research Report, FHWA-RD-00-038, FHWA, McLean, VA, 2000.
Soil Mechanics Design Manual 7.01
NAVFAC, "Soil Mechanics Design Manual 7.01," Naval Facilities Engineering Command,
Alexandria, VA, 1986.
Elastic Solutions for Soil and Rock Mechanics
- H G Poulos
- E H Davis
Poulos, H.G. and Davis, E.H., "Elastic Solutions for Soil and Rock Mechanics," John Wiley
and Sons, New York, 1974.
Selection of Spread Footings on Soils to Support Highway Bridge Structures
- N C Samtani
- E A Nowatzki
- D R Mertz
Samtani, N.C., Nowatzki, E.A., and Mertz, D.R., "Selection of Spread Footings on Soils to
Support Highway Bridge Structures," Report, FHWA-RC/TD-10-001, FHWA Resource
Center, Matteson, IL, 2010.
A new approach to the design of closely spaced geosynthetic reinforced soil for load bearing applications
- J E Nicks
- M Adams
- J Wu
Nicks, J.E., Adams, M., Wu, J., "A new approach to the design of closely spaced
geosynthetic reinforced soil for load bearing applications," TRB Annual Compendium of
Papers, Transportation Research Board, Washington DC., 2013a.
Implications of MSE Connection Criteria for Frictionally Connected GRS Structures
- J E Nicks
- M T Adams
Nicks, J.E., Adams, M.T., and Alzamora, D.A., "Implications of MSE Connection Criteria
for Frictionally Connected GRS Structures," Proceedings of Geosynthetics 2013, Long
Beach, CA, 2013b.
Design and Construction Guidelines for GRS Bridge Abutment with a Flexible Facing
- J T H Wu
- K Z Z Lee
- S B Helwany
- K Ketchart
Wu, J.T.H., Lee, K.Z.Z., Helwany, S.B., and Ketchart, K., "Design and Construction
Guidelines for GRS Bridge Abutment with a Flexible Facing," Report, No. 556, National
Cooperative Highway Research Program, Washington, DC, 2006.
153
Manuals for the Design of Bridge Foundations
- R M Barker
- J M Duncan
- K B Rojiani
- P S K Ooi
- C K Tan
- S G Kim
Barker, R.M., Duncan, J.M., Rojiani, K.B., Ooi, P.S.K., Tan, C.K., and Kim, S.G., "Manuals
for the Design of Bridge Foundations," NCHRP Report 343, Transportation Research Board,
Washington, DC, 1991.
LRFD design and construction of shallow foundations for highway bridges
- S G Paikowsky
- M C Canniff
- K Lesny
- A Kisse
- S Amatya
- R Muganga
Paikowsky, S.G., Canniff, M.C., Lesny, K., Kisse, A., Amatya, S., and Muganga, R., "LRFD
design and construction of shallow foundations for highway bridges," NCHRP Report 651,
Transportation Research Board, Washington DC, 2010.
Installation and ultraviolet exposure of geotextiles
- C V S Benjamin
- B S Bueno
- P C Lodi
- J G Zornberg
Benjamin, C.V.S., Bueno, B.S., Lodi, P.C. and Zornberg, J.G., "Installation and ultraviolet
exposure of geotextiles," Fourth European Geosynthetics Conference, EuroGeo4,
Edinburgh, United Kingdom, 8-10 September, 2008, pp. 18.
Load and Resistance Factor Design (LRFD) for Deep Foundations
- S G Paikowsky
- B Birgisson
- M Mcvay
- T Nguyen
- C Kuo
- G Baecher
- B Ayyab
- K Stenersen
- K O'malley
- L Chernauskas
- M Neill
Paikowsky, S. G., with contributions from Birgisson, B., McVay, M., Nguyen, T., Kuo, C.,
Baecher, G., Ayyab, B., Stenersen, K., O'Malley, K., Chernauskas, L., and O'Neill, M.,
"Load and Resistance Factor Design (LRFD) for Deep Foundations, NCHRP (Final) Report
507," Report, Transportation Research Board, Washington, DC, 2004.