The influence of backfill type and material properties on the performance of field-scale geosynth... more The influence of backfill type and material properties on the performance of field-scale geosynthetic reinforced soil (GRS) abutment models is investigated. Two alternative types of backfill as recommended in the Federal Highway Administration (FHWA) guidelines (called open-graded and well-graded) were used to build two field-scale model abutments and compare their load-bearing performance under a loading beam. Results are presented and discussed relative to the loading beam settlement, facing deformation and reinforcement strains. The well-graded backfill was found to result in smaller beam settlements and facing lateral deformations, especially at smaller loads that were comparable to service load levels. However, it was significantly faster and easier to compact the open-graded aggregate to the unit weight recommended in the guidelines. Nevertheless, performances of both abutment models were found to be satisfactory relative to the limiting requirements on the beam settlement and facing deformations at service load levels.
Backfill relative density can have a significant influence on the performance and stability of re... more Backfill relative density can have a significant influence on the performance and stability of reinforced soil retaining walls, as reflected in the form of minimum compaction requirements in current design guidelines. However, the quantitative influence of backfill relative density on the construction and serviceability performance of reinforced soil walls has not been examined adequately. In this study, centrifuge tests were carried out on two model walls with different backfill relative densities, and their measured performances were compared against those calculated using available empirical methods. Results of the study show that maximum displacement of the model with inadequate compaction (i.e. Dr = 65%) was 30% greater than that of the Dr = 95% model and exceeded the value predicted by one of the design methods examined. The foundation pressure underneath the wall showed increased magnitudes under the facing and a nonlinear decrease with distance from the facing along the backfill. Additionally, the model with Dr = 95% developed larger reinforcement loads and mobilized soil-reinforcement interface coefficient values relative to the model with Dr = 65%.
Abstract The paper presents a numerical modeling study on the upper-bound bearing capacity of foo... more Abstract The paper presents a numerical modeling study on the upper-bound bearing capacity of footing on back-to-back-Mechanically Stabilized Earth (MSE) walls using the finite element limit analysis (FELA) method. Numerical simulations were validated against results from other numerical simulation studies. Parametric analyses were carried out subsequently to examine the influences that the distance between reinforced zones, wall height, reinforcement design, and footing width and location could have on predicted bearing capacity and failure mechanism of back-to-back MSE walls. Results indicate that the influence of wall height on bearing capacity decreases with wall height. Additionally, a vertical slip plane could form along the back of reinforced zone in walls with tight reinforcement if the footing toe is located on the top of the retained zone. Finally, using a full-length top reinforcement layer (as opposed to lower-level layers) to connect the back-to-back walls is the most effective method to improve the bearing capacity of the structure subjected to footing load.
Sensor-enabled geogrid (SEGG) technology has been introduced by the authors in the past few years... more Sensor-enabled geogrid (SEGG) technology has been introduced by the authors in the past few years as a new category of geogrid products that possess embedded strain-sensing capability in addition to their conventional reinforcement/stabilization function in geotechnical and transportation applications. In this technology, the strain-sensing function of modified geogrids (SEGG products) arises from their tensoresistivity, which is the sensitivity of the polymer composite electrical conductivity to tensile strain. An SEGG product is filled with a target concentration of conductive fillers such as carbon blacks and carbon nanotubes. The authors' previous studies on SEGG to date were focused on the in-isolation performance of the unitized SEGG and the coating of yarn-type SEGG samples. In the continuation of a long-term study, this paper reported the latest findings on both the in-isolation and in-soil tensoresistivity performance of polyethylene terephthalate (polyester) yarn SEGG specimens that were coated with a strain-sensitive carbon black-filled PVC composite. The formulation of the coating composite was presented and the influences of the soil confining pressure and loading (i.e., strain) rate on the tensoresistivity and tensile strength of SEGG specimens were investigated. It was found that greater confining pressures and strain rates both result in a reduction in the tensoresistivity of the SEGG samples. However, both the magnitude and reproducibility of the measured tensoresistivity in the in-soil tests carried out in this study were judged to be acceptable for civil engineering applications, given that the accuracy of strain distributions in geogrids can be improved by increasing the number of strain data points in each reinforcement layer at a significantly lower cost compared to the conventional methods. It was thus concluded that the SEGG technology holds promise to serve as an alternative to conventional instruments for the performance monitoring of geotechnical structures.
Reinforcement plays an important role in seismic stability and performance of reinforced soil ret... more Reinforcement plays an important role in seismic stability and performance of reinforced soil retaining walls, and accurate assessment of reinforcement connection loads is an essential step in internal stability analysis of reinforced soil retaining walls using pseudo-static methods. However, the influence that the choice of wall facing could have on reinforcement connection loads is not adequately addressed in the current pseudo-static methods of analysis. In this study, two shaking table tests were carried out on full-height panel and modular block reinforced soil retaining wall models in order to examine the influence of facing type on the connection loads in the two models. The magnitudes and distributions of measured connection loads in the two models are compared with each other and against predictions from two pseudo-static methods. Results of this study shows that reinforcement connection loads are primarily influenced by the outward inertial force of the facing rather than dynamic earth pressure. Predicted connection loads from the Bathurst and the FHWA method showed better agreements with the measured results on the modular block and full-height panel wall models, respectively.
The potential benefit of placing a panel of compressible (i.e. expanded polystyrene) geofoam behi... more The potential benefit of placing a panel of compressible (i.e. expanded polystyrene) geofoam behind the reinforced zone of mechanically stabilized earth (MSE) walls is investigated using a numerical modeling approach. A panel of geofoam is placed immediately behind the reinforced zone during the construction phase of an idealized plane-strain reinforced soil segmental wall model. The analysis procedure includes the modeling of soil compaction. The magnitudes and distributions of earth pressure behind the reinforced zone in the wall models with and without the geofoam panel are compared to quantify the reductions in lateral earth pressure, resultant lateral force and overturning moment expected due to the placement of the geofoam material. Predicted magnitudes of facing lateral deformation and reinforcement strains are also compared among cases studied in order to evaluate the effect of geofoam on wall serviceability. It is shown that placing geofoam behind the reinforced zone can reduce the maximum lateral earth pressure behind this zone by as much as 50% depending on the geofoam thickness and stiffness values. The magnitudes of total lateral earth force (i.e. the resultant force of the lateral earth pressure distribution) behind the reinforced mass and overturning moment about the wall toe are shown to decrease by 31% and 26%, respectively. These findings point to a significant potential for using geofoam to reduce the lateral earth pressure demand on MSE walls (i.e. as opposed to rigid retaining walls examined previously) and thereby increase their serviceability and their factors of safety against external instability.
PDFTech ReportFHWA-OK-13-09ODOT SP&R Item Number 2227EmbankmentsBridge approachesSlabsFoundat... more PDFTech ReportFHWA-OK-13-09ODOT SP&R Item Number 2227EmbankmentsBridge approachesSlabsFoundationsSoilsSettlement (Structures)Data analysisTestingOklahomaUniversity of Oklahoma. School of Civil Engineering and Environmental ScienceMiller, Gerald A.Hatami, KianooshCerato, Amy B.Osborne, ColinUniversity of Oklahoma. School of Civil Engineering and Environmental ScienceOklahoma. Dept. of Transportation. Planning & Research DivisionUS Transportation CollectionApproach embankment settlement is a pervasive problem in Oklahoma and many other states. The bump and/or abrupt slope change poses a danger to traffic and can cause increased dynamic loads on the bridge. Frequent and costly maintenance may be needed or extensive repair and reconstruction may be required in extreme cases. Research critically investigated the design and construction methods in Oklahoma to reveal causes and solutions to the bridge approach settlement problem. The major objectives of the research were: 1) Investigate causes of, and solutions to the approach slab settlement problem in available literature. 2) By direct investigation, determine primary causes of approach slab settlement for selected bridges in Oklahoma. Bridge configurations studied included those commonly used by ODOT and representing different embankment and foundation soil conditions typically encountered in Oklahoma. 3) Recommend solutions to minimize or eliminate approach slab settlement problems associated with Oklahoma bridges. 4) Recommend construction solutions to minimize potential for approach settlement problems. The major tasks completed included: 1) A review of available published literature related to the bridge approach settlement problem. 2) A survey of ODOT Field Divisions to solicit information about bridge sites experiencing settlement problems. In addition, potential sites were identified through discussions with key persons in the ODOT Materials Division. 3) Of the potential test sites, field reconnaissance investigations were conducted for 30 bridges at 22 separate locations in Oklahoma. These sites were identified as having moderate to severe problems and were representative of different bridge types, different geology, and different ages. To the extent possible, design, construction and maintenance records were obtained for these bridges. 4) At five of the test sites, subsurface investigation was conducted including: drilling and sampling, cone penetrometer testing, laboratory classification testing and oedometer testing to determine settlement parameters. 5) Statistically analyzed data to determine if there were relationships observed between bridge / embankment / foundation features and observed distresses. 6) Analyzed settlement of foundation soils and wetting-induced collapse settlement in embankment soils. 7) Developed recommendations for design and construction methods for addressing the approach slab settlement problem. The investigation revealed that erosion under the approach slab and under the abutment is a serious problem for many Oklahoma bridges. Consolidation of foundation soils was also found to be an important contributor to the approach slab settlement problem
The paper reports results of numerical simulation of reinforced propped panel walls subjected to ... more The paper reports results of numerical simulation of reinforced propped panel walls subjected to base shaking. The paper extends the results of earlier simulation work reported by the writers. In the current study the effects of wall height, reinforcement stiffness and spacing on the dynamic response of model walls are reported. The simulated reinforced wall structures were 3, 6, and 9 m in height and seated on a rigid foundation. The facing panels were pinned at the toe. A variable-amplitude harmonic motion with the frequency of 3 Hz and a peak horizontal acceleration of 0.2 g was applied at the foundation. The two-dimensional, explicit dynamic finite difference program Fast Lagrangian Analysis of Continue (FLAC) was used to carry out the numerical experiments. Numerical simulations of the type reported here hold promise to verify or modify current pseudostatic methods of seismic analysis and design of reinforced walls.
The influence of backfill type and material properties on the performance of field-scale geosynth... more The influence of backfill type and material properties on the performance of field-scale geosynthetic reinforced soil (GRS) abutment models is investigated. Two alternative types of backfill as recommended in the Federal Highway Administration (FHWA) guidelines (called open-graded and well-graded) were used to build two field-scale model abutments and compare their load-bearing performance under a loading beam. Results are presented and discussed relative to the loading beam settlement, facing deformation and reinforcement strains. The well-graded backfill was found to result in smaller beam settlements and facing lateral deformations, especially at smaller loads that were comparable to service load levels. However, it was significantly faster and easier to compact the open-graded aggregate to the unit weight recommended in the guidelines. Nevertheless, performances of both abutment models were found to be satisfactory relative to the limiting requirements on the beam settlement and facing deformations at service load levels.
Backfill relative density can have a significant influence on the performance and stability of re... more Backfill relative density can have a significant influence on the performance and stability of reinforced soil retaining walls, as reflected in the form of minimum compaction requirements in current design guidelines. However, the quantitative influence of backfill relative density on the construction and serviceability performance of reinforced soil walls has not been examined adequately. In this study, centrifuge tests were carried out on two model walls with different backfill relative densities, and their measured performances were compared against those calculated using available empirical methods. Results of the study show that maximum displacement of the model with inadequate compaction (i.e. Dr = 65%) was 30% greater than that of the Dr = 95% model and exceeded the value predicted by one of the design methods examined. The foundation pressure underneath the wall showed increased magnitudes under the facing and a nonlinear decrease with distance from the facing along the backfill. Additionally, the model with Dr = 95% developed larger reinforcement loads and mobilized soil-reinforcement interface coefficient values relative to the model with Dr = 65%.
Abstract The paper presents a numerical modeling study on the upper-bound bearing capacity of foo... more Abstract The paper presents a numerical modeling study on the upper-bound bearing capacity of footing on back-to-back-Mechanically Stabilized Earth (MSE) walls using the finite element limit analysis (FELA) method. Numerical simulations were validated against results from other numerical simulation studies. Parametric analyses were carried out subsequently to examine the influences that the distance between reinforced zones, wall height, reinforcement design, and footing width and location could have on predicted bearing capacity and failure mechanism of back-to-back MSE walls. Results indicate that the influence of wall height on bearing capacity decreases with wall height. Additionally, a vertical slip plane could form along the back of reinforced zone in walls with tight reinforcement if the footing toe is located on the top of the retained zone. Finally, using a full-length top reinforcement layer (as opposed to lower-level layers) to connect the back-to-back walls is the most effective method to improve the bearing capacity of the structure subjected to footing load.
Sensor-enabled geogrid (SEGG) technology has been introduced by the authors in the past few years... more Sensor-enabled geogrid (SEGG) technology has been introduced by the authors in the past few years as a new category of geogrid products that possess embedded strain-sensing capability in addition to their conventional reinforcement/stabilization function in geotechnical and transportation applications. In this technology, the strain-sensing function of modified geogrids (SEGG products) arises from their tensoresistivity, which is the sensitivity of the polymer composite electrical conductivity to tensile strain. An SEGG product is filled with a target concentration of conductive fillers such as carbon blacks and carbon nanotubes. The authors' previous studies on SEGG to date were focused on the in-isolation performance of the unitized SEGG and the coating of yarn-type SEGG samples. In the continuation of a long-term study, this paper reported the latest findings on both the in-isolation and in-soil tensoresistivity performance of polyethylene terephthalate (polyester) yarn SEGG specimens that were coated with a strain-sensitive carbon black-filled PVC composite. The formulation of the coating composite was presented and the influences of the soil confining pressure and loading (i.e., strain) rate on the tensoresistivity and tensile strength of SEGG specimens were investigated. It was found that greater confining pressures and strain rates both result in a reduction in the tensoresistivity of the SEGG samples. However, both the magnitude and reproducibility of the measured tensoresistivity in the in-soil tests carried out in this study were judged to be acceptable for civil engineering applications, given that the accuracy of strain distributions in geogrids can be improved by increasing the number of strain data points in each reinforcement layer at a significantly lower cost compared to the conventional methods. It was thus concluded that the SEGG technology holds promise to serve as an alternative to conventional instruments for the performance monitoring of geotechnical structures.
Reinforcement plays an important role in seismic stability and performance of reinforced soil ret... more Reinforcement plays an important role in seismic stability and performance of reinforced soil retaining walls, and accurate assessment of reinforcement connection loads is an essential step in internal stability analysis of reinforced soil retaining walls using pseudo-static methods. However, the influence that the choice of wall facing could have on reinforcement connection loads is not adequately addressed in the current pseudo-static methods of analysis. In this study, two shaking table tests were carried out on full-height panel and modular block reinforced soil retaining wall models in order to examine the influence of facing type on the connection loads in the two models. The magnitudes and distributions of measured connection loads in the two models are compared with each other and against predictions from two pseudo-static methods. Results of this study shows that reinforcement connection loads are primarily influenced by the outward inertial force of the facing rather than dynamic earth pressure. Predicted connection loads from the Bathurst and the FHWA method showed better agreements with the measured results on the modular block and full-height panel wall models, respectively.
The potential benefit of placing a panel of compressible (i.e. expanded polystyrene) geofoam behi... more The potential benefit of placing a panel of compressible (i.e. expanded polystyrene) geofoam behind the reinforced zone of mechanically stabilized earth (MSE) walls is investigated using a numerical modeling approach. A panel of geofoam is placed immediately behind the reinforced zone during the construction phase of an idealized plane-strain reinforced soil segmental wall model. The analysis procedure includes the modeling of soil compaction. The magnitudes and distributions of earth pressure behind the reinforced zone in the wall models with and without the geofoam panel are compared to quantify the reductions in lateral earth pressure, resultant lateral force and overturning moment expected due to the placement of the geofoam material. Predicted magnitudes of facing lateral deformation and reinforcement strains are also compared among cases studied in order to evaluate the effect of geofoam on wall serviceability. It is shown that placing geofoam behind the reinforced zone can reduce the maximum lateral earth pressure behind this zone by as much as 50% depending on the geofoam thickness and stiffness values. The magnitudes of total lateral earth force (i.e. the resultant force of the lateral earth pressure distribution) behind the reinforced mass and overturning moment about the wall toe are shown to decrease by 31% and 26%, respectively. These findings point to a significant potential for using geofoam to reduce the lateral earth pressure demand on MSE walls (i.e. as opposed to rigid retaining walls examined previously) and thereby increase their serviceability and their factors of safety against external instability.
PDFTech ReportFHWA-OK-13-09ODOT SP&R Item Number 2227EmbankmentsBridge approachesSlabsFoundat... more PDFTech ReportFHWA-OK-13-09ODOT SP&R Item Number 2227EmbankmentsBridge approachesSlabsFoundationsSoilsSettlement (Structures)Data analysisTestingOklahomaUniversity of Oklahoma. School of Civil Engineering and Environmental ScienceMiller, Gerald A.Hatami, KianooshCerato, Amy B.Osborne, ColinUniversity of Oklahoma. School of Civil Engineering and Environmental ScienceOklahoma. Dept. of Transportation. Planning & Research DivisionUS Transportation CollectionApproach embankment settlement is a pervasive problem in Oklahoma and many other states. The bump and/or abrupt slope change poses a danger to traffic and can cause increased dynamic loads on the bridge. Frequent and costly maintenance may be needed or extensive repair and reconstruction may be required in extreme cases. Research critically investigated the design and construction methods in Oklahoma to reveal causes and solutions to the bridge approach settlement problem. The major objectives of the research were: 1) Investigate causes of, and solutions to the approach slab settlement problem in available literature. 2) By direct investigation, determine primary causes of approach slab settlement for selected bridges in Oklahoma. Bridge configurations studied included those commonly used by ODOT and representing different embankment and foundation soil conditions typically encountered in Oklahoma. 3) Recommend solutions to minimize or eliminate approach slab settlement problems associated with Oklahoma bridges. 4) Recommend construction solutions to minimize potential for approach settlement problems. The major tasks completed included: 1) A review of available published literature related to the bridge approach settlement problem. 2) A survey of ODOT Field Divisions to solicit information about bridge sites experiencing settlement problems. In addition, potential sites were identified through discussions with key persons in the ODOT Materials Division. 3) Of the potential test sites, field reconnaissance investigations were conducted for 30 bridges at 22 separate locations in Oklahoma. These sites were identified as having moderate to severe problems and were representative of different bridge types, different geology, and different ages. To the extent possible, design, construction and maintenance records were obtained for these bridges. 4) At five of the test sites, subsurface investigation was conducted including: drilling and sampling, cone penetrometer testing, laboratory classification testing and oedometer testing to determine settlement parameters. 5) Statistically analyzed data to determine if there were relationships observed between bridge / embankment / foundation features and observed distresses. 6) Analyzed settlement of foundation soils and wetting-induced collapse settlement in embankment soils. 7) Developed recommendations for design and construction methods for addressing the approach slab settlement problem. The investigation revealed that erosion under the approach slab and under the abutment is a serious problem for many Oklahoma bridges. Consolidation of foundation soils was also found to be an important contributor to the approach slab settlement problem
The paper reports results of numerical simulation of reinforced propped panel walls subjected to ... more The paper reports results of numerical simulation of reinforced propped panel walls subjected to base shaking. The paper extends the results of earlier simulation work reported by the writers. In the current study the effects of wall height, reinforcement stiffness and spacing on the dynamic response of model walls are reported. The simulated reinforced wall structures were 3, 6, and 9 m in height and seated on a rigid foundation. The facing panels were pinned at the toe. A variable-amplitude harmonic motion with the frequency of 3 Hz and a peak horizontal acceleration of 0.2 g was applied at the foundation. The two-dimensional, explicit dynamic finite difference program Fast Lagrangian Analysis of Continue (FLAC) was used to carry out the numerical experiments. Numerical simulations of the type reported here hold promise to verify or modify current pseudostatic methods of seismic analysis and design of reinforced walls.
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