| dc.description.abstract | **Please note that the full text is embargoed until 06/07/2024** ABSTRACT: The unpredictability of the stability of embankment slopes is a recurring problem that threatens the safety of the traveling public, as it compromises the integrity of the structures built on them. Slopes that undergo seasonal variations of stream flow are of particular concern, as they are usually located under a bridge structure that spans a stream, and the meandering of the stream flow, the seasonal variations of the flow depth, and the velocity in the channel induce scouring and increase the risk of the bridge failing. Departments of transportation have long attempted to address these concerns by designing systems that are economical, environmentally friendly, and impose the lowest possible impact on flood plains and rights of way. The performance of the methods that have been implemented for the past several decades has not been comprehensively measured in the field, however, which means that there is very little information about how they actually function. The lack of information on the design methods and performance of most of the slope stability systems currently in existence magnifies the need for in-depth research and development.
The Fort Worth District of the Texas Department of Transportation (TxDOT) plans to reconstruct and widen IH-20 over the Clear Fork of the Trinity River in Benbrook, Texas by designing and installing a slope stabilization system that uses percussion driven earth anchors (PDEAs), erosion protection envelopes, and articulating concrete blocks over the channel banks. The selection of this system by TxDOT is based on its compatibility with steep slopes and its ability to mitigate the impacts of flood plains.
PDEAs are a viable, sustainable, cost effective, and environmentally friendly solution for unstable slopes in areas prone to stream flow, but there is limited information about the effectiveness of the system selected by TxDOT, Duckbill 138 II PDEA, for stabilizing riverbank slopes. There is also a dearth of clear information on its suitability for different types of soil, load locking, ultimate pullout capacity, and in-service performance during the design and construction phase of the PDEA. Thus, the responsibility for recommending the tensioning load is that of the contractor and system provider, which often leads to lengthy discussions among TxDOT employees, the contractor, and suppliers, and results in delays and additional project costs.
This study focuses on utilizing PDEAs to stabilize channel bank slopes by briefly exploring what is customarily used to stabilize channel bank slopes in Texas and then investigating the benefits of using the percussion driven earth anchor system for this purpose. Comprehensive field instrumentation and laboratory testing was performed to evaluate and measure the performance of the PDEAs installed along IH-20 over the Clear Fork of the Trinity channel bank slope, where a series of PDEAs approximately 12.5 feet long are arranged 4 feet by 4 feet on center and surface-treated with geotextiles, wire mesh, and articulating concrete blocks (ACBs). The effects of seasonal variations on the reinforced section of the slope were analyzed by considering the data from the comprehensive instrumentation of the PDEA, ACBs, and the slope. The soils at the project site were tested in the laboratory, utilizing basic soil exploration tests, the standard Proctor test, constant head permeability test, direct shear test, ring shear test, and others. The effects of the submerged condition during extreme flood conditions with drawdown conditions were numerically modeled, studied, and analyzed using Bentley’s Plaxis-2D finite element software. Statistical regression analysis was conducted to fit the major significant variables, such as undrained shear strength, Texas cone penetration blow counts, and depth of installation, to create a best-fit linear regression model for planning and design purposes. A parametric study was done to evaluate the impact of the PDEA by using statistical models and FEM Plaxis-2D.
The laboratory and field tests revealed that the behavior and pull-out performance of the PDEA system implemented on the IH-20 project was excellent, even under varying seasonal wetting and drying and other climatic conditions that occurred during the evaluation period, from mid-2022 to mid-2023. It is anticipated that the system will continue to demonstrate good performance.
The thorough evaluation of the system through experimental, statistical, and numerical studies, as well as personal observation of the construction of the system, enabled the development of a succinct design and construction guideline for future installations of comparable systems. Guidelines were also developed for use by construction contractors and managers. Finally, the effect of seasonal wetting and drying, including loss of working load within the system, is included as part of this study. | |
