Elsevier

Transportation Geotechnics

Volume 30, September 2021, 100596
Transportation Geotechnics

Finite element limit analysis of bearing capacity of footing on back-to-back reinforced soil retaining walls

https://doi.org/10.1016/j.trgeo.2021.100596Get rights and content

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.

Introduction

Reinforced soil walls (alternatively known as Mechanically Stabilized Earth, MSE walls) are successfully used in a wide range of projects, including railways and highways. The performance of MSE walls subjected to surcharge loads have been examined in recent years. Hatami and Bathurst [6] reported experimental data and numerical simulation results on heavily instrumented large-scale MSE walls, which were subjected to surcharge load in an indoor laboratory. They concluded that predicted results were in reasonable agreement with those from model tests relative to a wide range of measurements including facing displacements, toe loads, foundation pressures, connection loads, and reinforcement strains. Yoo and Kim [24] carried out surcharge load tests on large-scale MSE walls and found that reinforcement loads were more significant closer to the surcharge load. Ehrlich et al. [4] carried out model tests on MSE walls that were constructed using different backfill compaction efforts. They observed that any differences in the mobilized reinforcement load due to differences in compaction efforts during construction would dissipate at larger surcharge loads. Liu [12] proposed an analytical method to calculate reinforcement load under surcharge loads that included soil-reinforcement interaction, in addition to the soil dilation and nonlinear behavior. Xie et al. [18] proposed a limit equilibrium method to evaluate the bearing capacity of MSE structures. They concluded that a log-spiral failure mechanism would most likely occur in the reinforced zone if lower-strength reinforcement was used in the wall. Zheng et al. [25] reported test results on large-scale Geosynthetic Reinforced Soil (GRS) model abutments. They found that maximum strains occurred near the facing in lower reinforcement layers, but they were observed underneath the beam seat in the upper layers in their model abutment. Xu et al. [21] carried out numerical simulations on two-tiered MSE walls and determined that their bearing capacity could reach a minimum when the footing was placed just outside the reinforced zone of the upper wall. Xu et al. [22] proposed an upper bound method based on a y-shaped failure mechanism to calculate the bearing capacity of GRS abutments under footing load. They found that reinforcement vertical spacing would have a diminished influence on bearing capacity in more widely-spaced abutment models.

In contrast to the single MSE walls discussed above, there are many situations where MSE walls are constructed in a back-to-back configuration, such as embankments approaching bridges [5] and those supporting railroads [10]. Han and Leshchinsky [5] carried out numerical simulations on back-to-back MSE walls and found that the demand on reinforcement tensile strength was higher when the walls were farther apart from each other. Benmebarek et al. [1] investigated the influence of wall geometry on the stability of back-to-back MSE walls using a finite element analysis, and compared their numerical simulation results with those from FHWA design guidelines [2]. They concluded that horizontal earth pressures from the FHWA guidelines underestimated the actual values in closely-spaced back-to-back walls. Rajagopal and Thiyyakkandi [13] reported numerical simulation results on back-to-back MSE walls built with different zones of marginal and select fills (i.e., hybrid-fill). They found that reinforcement loads in the hybrid-fill wall were significantly lower than those in a comparable model built with a fully marginal fill.

Many times, MSE walls are constructed to support surcharge loads. The bearing capacity of single MSE walls have been investigated extensively in the past. However, similar studies on back-to-back MSE walls are not as commonly available. In this study, a finite element limit analysis (FELA) method is used to investigate the performance of back-to-back MSE walls under footing load. The numerical model is first validated against results from numerical simulations. Parametric analyses are then carried out to investigate the influences that distance between the reinforced zones of two walls, wall height, reinforcement design, and footing width and location could have on the predicted upper-bound bearing capacity and failure mechanism of back-to-back MSE walls.

Section snippets

Methodology

Limit Analysis (LA) method is a powerful tool for the stability analysis of earth structures [16]. The traditional upper bound theorem within the LA states that the energy dissipated by any kinematically admissible velocity field can be equated to the energy dissipated by the external loads [9], [23]. In recent years, the finite element limit analysis (FELA) has been developed to overcome the shortcomings of the traditional limit analysis requiring that a possible failure mechanism would need

Parametric analysis on bearing capacity and slip planes in the backfill

Field examples of the type of footing on MSE walls include concrete pavement-aggregate base structures used on embankments and ramps in highway and railway applications [10] as shown in Fig. 2a. A parametric study was carried out in this section to investigate the influences of distance between reinforced zones, wall height, reinforcement properties, footing width and location, and backfill shear strength on the predicted upper-bound bearing capacity of footing on back-to-back-MSE walls. The

Conclusions

In this study, a method was used to investigate the upper-bound bearing capacity of footing on back-to-back-MSE walls under footing load. Results from the FELA method in this study were compared with those from previous studies, which showed reasonable agreement. An extensive parametric study was subsequently carried out to investigate the influences of the distance between reinforced zones, wall height, footing width and location, and reinforcement design on the predicted slip planes and

CRediT authorship contribution statement

Peng Xu: Conceptualization, Methodology, Validation, Data curation, Writing - original draft, Writing - review & editing, Visualization. Guangqing Yang: Methodology, Data curation, Writing - review & editing, Project administration. Ting Li: Formal analysis, Investigation, Data curation, Visualization, Writing - original draft. Kianoosh Hatami: Methodology, Validation, Writing - review & editing, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This study is funded by Science and Technology Project of Hebei Education Department (NO. ZD2021096;QN2021127).

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