Numerical parametric study of geosynthetic reinforced soil integrated bridge system (GRS-IBS)

https://doi.org/10.1016/j.geotexmem.2020.10.005Get rights and content

Highlights of Article

  • Geosynthetic reinforced soil integrated bridge system (GRS-IBS).

  • Finite element numerical modeling.

  • Parametric study.

  • Lateral facing deformation.

  • Reinforcement strain.

Abstract

A 2-D finite flement model was developed in this study to conduct a FE parametric study on the effects of some variables in the performance of geosynthetic reinforced soil integrated bridge system (GRS-IBS). The variables investigated in this study include the effect of internal friction angle of backfill material, width of reinforced soil foundation (RSF), secondary reinforcement within bearing bed, setback distance, bearing width and length of reinforcement. Other important parameters such as reinforcement stiffness and spacing were previously investgated by the authors. The performance of GRS-IBS were investgated in terms of lateral facing displacement, strain distribution along reinforcement, and location of potential failure zone. The results showed that the internal friction angle of backfill material has a significant impact on the performance of GRS-IBS. The secondary reinforcement, setback distance, and bearing width have low impact on the performance of GRS-IBS. However, it was found that the width of RSF and length of reinforcement have negligible effect on the performance of GRS-IBS. Finally, the potential failure envelope of the GRS-IBS abutment was found to be a combination of punching shear failure envelope (top) that starts under the inner edge of strip footing and extends vertically downward to intersect with Rankine active failure envelope (bottom).

Introduction

Geosynthetic reinforced soil (GRS) can be defined as a special reinforced soil with closely-spaced geosynthetic fabric installed in layers as a soil stabilization, which is considered an alternative design method to the conventional bridge support technology. Although the GRS has been around for years, its application as part of integrated bridge system (IBS) is fairly new. Using the geosynthetics as reinforcement in retaining walls, slopes and embankment started many years ago (i.e., Allen et al., 1992). The Geosynthetic Reinforced Soil (GRS) walls and Mechanically Stabilized Earth Walls (MSE) are getting more attention these days over the traditional concrete walls due to the ease of construction, cost saving, reduction in construction time (Adams et al., 2011), and their sustainability (Damians et al. 2016). Abu Hejleh et al. (2000) argued that the GRS and MSE walls can successfully support the roadway structures and traffic loads in addition to the self-weight of the backfill soil. Recently, many GRS-IBS bridge abutments have been monitored using field instrumentations such as (Gebremariam et al., 2020).

According the Federal Highway Administration (FHWA), the GRS-IBS usually includes GRS abutment, GRS integrated approach, bearing bed, and reinforced soil foundation (Adams et al., 2011). One important difference between the GRS and the MSE walls is that the reinforcement tensions and soil stresses are assembled in a different way than in the case of MSE walls, and using closer reinforcement spacing than MSE walls. The main difference between the MSE walls and the GRS walls is that the MSE walls are considered externally supported systems, in which the facing block is structurally connected to the reinforcement; while the GRS walls are internally supported systems, in which the facing block is not a structure element but rather an aesthetic component (façade). Wu (2007) introduced the “bin pressure” concept to estimate the lateral earth pressure of tightly reinforced soils at the facing. He found out that the lateral earth pressure mainly depends on the reinforcement spacing rather than the height of the GRS wall.

Another difference between the GRS wall and GRS abutment is that the GRS abutment is usually subjected to a larger surcharge from bridge loads. Therefore, meeting an allowable bearing pressure within the bearing bed below the bridge girders is an important issue for design. The FHWA adopted two different procedures to design the capacity of the GRS abutment. The first approach is based on the analytical design method that was developed by Wu et al. (2013) to incorporate the reinforcement spacing, confinement caused by facing rigidity, aggregate size, tensile strength, and backfill soil friction angle in the design. The second design approach is based on the results of experimentally determined vertical stress-strain relationship from performance tests (i.e., GRS mini-pier loading tests) conducted using project-specific geosynthetic reinforcement and backfill soil. According to FHWA guidelines, the ultimate bearing capacity is determined at 5% vertical strain, and a maximum allowable bearing pressure of 200 kPa for GRS abutments (Berg et al., 2009; Adams et al., 2011).

According to literature, numerical methods such as finite element or finite difference techniques had been extensively used for analyzing the behavior of GRS walls (i.e., Liu, 2015; Bathurst et al., 2006, Ardah et al., 2017; Abu Farsakh et al., 2018, 2019). The use of numerical methods to simulate complex geotechnical engineering problems has many advantages such as obtaining more comprehensive results, evaluating the effects of different loading conditions, and study the effect of different variables and parameters contributing to the performance of geotechnical problem, which are difficult and very costly to achieve in the laboratory and/or field tests.

The literature reveals that few numerical studies were conducted to evaluate the behavior of GRS-IBS, comparing to the free-standing geosynthetic MSE walls (e.g., Bathurst et al., 2000, 2001, 2006; Wu et al., 2006, 2014; Liu, 2015; Zheng and Fox, 2016, 2017; Bathurst and Allen, 2016; Ardah et al., 2017; Abu Farsakh et al., 2018, 2019). Wu et al. (2006) investigated the allowable bearing pressure on bridge sills over a GRS abutment using the finite element analysis. They simulated 72 different cases in their study for different geometric and materials properties: sill type and width, soil properties, reinforcement spacing, and foundation stiffness. Their results showed that the reinforcement spacing plays a significant role on the performance of the GRS in terms of lateral deformation and the capacity of the GRS abutment. Wu et al. (2014) developed a finite element model to evaluate the composite behavior of tightly-spaced reinforcement soil. They investigated the effect of reinforcement spacing and stiffness, and soil properties on the soil dilation. They found out that the inclusion of geosynthetic caused a reduction in soil dilation (suppress soil) and lead to a stronger soil composite with zero volume change assumption when the reinforcement spacing is less than 0.3 m, which was adopted by the FHWA for estimating the lateral deformation of GRS abutment. Zheng and Fox (2016, 2017) investigated the performance of GRS abutments under static loading conditions using the finite-difference numerical analyses, in which they conducted FE parametric study. Their model was verified using the field measurement of the Founders/Meadows GRS bridge abutment (Abu-Hejleh et al., 2002). The results of their numerical parametric study showed that the reinforcement spacing, the backfill compaction, and the bridge load have significant influence on the lateral facing deformations and bridge foundation settlement of the GRS abutments. They also found out that the reinforcement stiffness, bridge load, and the abutment height are the most significant factors on the performance of the GRS-IBS under static loading.

Other numerical parametric studies have been conducted to evaluate the performance of the GRS-IBS bridge abutment under service load conditions (e.g., Zheng and Fox., 2017; Ardah et al., 2017). However, these studies focused on evaluating the effects of reinforcement spacing, reinforcement strength, span length, and abutment height. In a previous study (Abu-Farsakh et al., 2019), the authors investigated the effects of GRS-IBS abutment height, span length, reinforcement stiffness, and reinforcement spacing on the performance of GRS-IBS. In this paper, the authors will investigate the effects of other important design parameters such as the effects of internal friction angle, φ, of backfill material, width of reinforced soil foundation (RSF), BRSF, secondary reinforcement within bearing bed, setback distance, ab, bearing width, b, and length of reinforcement, Lr. In addition, this study will also discuss the magnitude and location of maximum strains along reinforcements and the location of potential failure envelope, which were not investigated in the previous studies.

Section snippets

Objective

The main objective of this study is to conduct FE parametric study to evaluate the effect of different parameters on the performance of GRS-IBS in terms of lateral facing deformation and reinforcement strain. The parameters investigated in this paper are: internal friction angle, φ, of fill material, width of reinforced soil foundation (RSF), BRSF, secondary reinforcement within bearing bed, setback distance, ab, bearing width, b, and length of reinforcement, Lr. The locus of maximum strain

Mesh, geometry and boundary conditions

A 2-D FE model was developed in this study using PLAXIS 2D 2016 (Brinkgreve, 2002) software in order to investigate the effect of some important parameters on the performance of GRS-IBS in terms of lateral facing displacement, strain distribution along reinforcement, and envelope of maximum strain. The FE model was first verified using the measurements of field monitoring of a fully instrumented GRS-IBS abutment at Maree Michel GRS Bridge in Louisiana (Saghebfar et al. 2017a, 2017b). The

FE parametric study

Six different parameters were considered in this study to investigate the effects of these parameters on the performance of the GRS-IBS under service loading condition in terms of lateral facing displacement, maximum strain along geosynthetic reinforcement, and the envelope of maximum strains. The selected parameters are: internal friction angle, φ, of backfill material, width of reinforced soil foundation (RSF), BRSF, secondary reinforcement within bearing bed, setback distance, ab, bearing

Summary and conclusions

A 2D FE parametric study was conducted in this paper to investigate the effects of selected parameters on the performance of the GRS-IBS in terms of lateral facing deformation, magnitude and distribution of reinforcement strains, and potential location of failure envelope (i.e., locus of maximum strain). The parameters included in this FE study are the effect of internal friction angle, φ, of backfill material, width of reinforced soil foundation (RSF), BRSF, secondary reinforcement within the

Acknowledgment

This research project is funded by the Louisiana Department of Transportation and Development (State SIO No. 30000981) and Louisiana Transportation and Research Center (LTRC Project No. 13-5 GT).

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