United States Department of Transportation
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Monitoring of In-Service Geosynthetic Reinforced Soil (GRS) Bridge Abutments in Louisiana
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2020-01-01
[PDF-6.78 MB]
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Edition:Final Report, October 2013 to Dec 2018
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Abstract:The Federal Highway Administration (FHWA) has been promoting the Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) technology for bridge abutments through the Every Day Counts (EDC) initiative. To realize the potential benefits of using GRS-IBS abutments in Louisiana, the Department of Transportation and Development (DOTD) built GRS-IBS abutment for two bridges at Creek and Maree Michel in Vermilion Parish, which provided the opportunity to examine the performance and stability of GRS-IBS abutments with respect to local materials and soil conditions. An instrumentation plan was developed to monitor the short-term and long-term behavior of one of the GRS-IBS abutments. Measurements from the instrumentation provided valuable information on the performance of GRS-IBS abutments. The FHWA design of GRS-IBS abutments was verified and calibrated based on the collected data from the instrumentation measurements. Furthermore, the long-term monitoring provides the measurements needed to examine the performance, durability and long-term stability of the GRS-IBS abutments constructed over Louisiana subsurface soil, under the live traffic load and adverse weather conditions in Louisiana. The monitoring program consisted of measuring bridge deformations, settlement, strains along the reinforcement, vertical and horizontal stresses within abutment, and pore water pressure. Measurements from the instrumentations provide valuable information to evaluate the design procedure and performance of GRS-IBS bridges. The instrumentation readings showed that the magnitude and distribution of strains along reinforcements vary with depth. The locus of maximum strains in the abutment varied by surcharge load and time that did not correspond to the (45+ϕ/2) line, especially after the placement of steel girders. A comparison was made between the measured and theoretical value of thrust forces on the facing wall showed that the predicted loads by the bin pressure theory were close to the measured loads in the lower level of abutment. However, the bin pressure theory under predicted the thrust loads in the upper layers with reduced reinforcement spacing. Researchers developed 2D and 3D finite elements (FE) models using PLAXIS 2016 program to evaluate the performance of GRS abutment. The hardening soil model proposed by Schanz et al. was used to simulate the backfill materials, the linear-elastic with Mohr-Coulomb (M-C) failure criterion model was used to simulate the interface between the geosynthetic and backfill materials, and both the geosynthetic and the facing block were modeled using linear elastic model [1]. The FE models were first verified using the field test measurements. Then, a 2D FE parametric study was conducted to evaluate the effect of different variables and parameters on the performance of the GRS-IBS under service loading, in terms of lateral displacement of facing, settlement of RSF, maximum strain distribution along the reinforcement, lateral facing pressure, and location of possible failure locus. The FE results showed that that the abutment height, span length, reinforcement spacing Sv, and reinforcement stiffness have significant effect on the performance of the GRS-IBS. The effect of reinforcement spacing has higher influence than the reinforcement stiffness for the same reinforcement ratio (stiffness/ spacing) due to the composite behavior of closely reinforced soil.
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