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Earth Retaining Structures and Asset Management

Earth Retaining Structures (ERS) are an often-overlooked critical component of America's surface transportation network. Current applications of ERS in highway projects accelerate construction, reduce costs, and enable the use of complex geometric designs. ERS elements also enable vehicles to travel at increased speeds, reduce congestion, and lessen the environmental impact of highway and bridge construction. Ultimately, ERS serve as a vital tool in the successful movement of people and goods.

A Significant and Growing Asset Investment

With the initial cost of building ERS often reaching or exceeding $100 per square foot of surface area, the total construction cost of the nation's ERS network is enormous. The demand for ERS on America's highways and bridges is only expected to increase in the future. Today, the construction of a single complex urban interchange routinely requires tens of thousands of square feet of ERS. The increased demand for ERS in transportation applications has been accompanied by the development of new materials and systems for design and construction.

Permanent ERS, which may vary in height from 4 feet to more than 100 feet, are built to withstand significant technical demands and to resist very large forces. ERS often have assumed design lives of 100 years, but knowledge of actual design life for these structures is minimal and failures that have occurred to date have happened without warning. Repairing these failed structures is very expensive, complex, and difficult to implement. Repairs of even single, moderately sized ERS installations often cost millions of dollars.

Loss of life due to failed ERS has been rare but safety remains a primary concern, as most ERS installations either directly support bridge components or roadways, or support ground and other transportation features that are immediately adjacent to a bridge or highway. While the transportation community's knowledge of deterioration mechanics and methods to assess in-service performance has been limited to date, asset management (AM) offers important tools and techniques to help in evaluating ERS assets.

An Essential Part of an Asset Management Program

When developing long- and short-term programming and budgeting plans, it is critical that transportation agencies start with clearly identified inventories and condition assessments. AM plans must be data driven and must include performance measures that relate to policy objectives. Engineering and economic analysis and risk assessment are especially important when trade-off decisions are made on how to best address the transportation agency's many needs, as well as in support of which projects will be funded based upon quality information and analysis.

As states and other transportation infrastructure owners determine and prioritize their highway needs, they can use transportation asset management (TAM) techniques and data tools to collect and analyze data, measure system performance, identify strategies, set goals, develop effective performance measures, and support integrated decisions in programming projects. ERS should be included in a TAM program, along with pavements, bridges, and ancillary structures to help ensure optimal usage of limited funding.

Questions that can be answered if your agency uses TAM techniques and data tools to inventory and evaluate its ERS network include:

• How many earth retaining structures (ERS) does your agency own?
• How old are the structures?
• What is their condition and what is their remaining service life?
• What is the likelihood that one will collapse or experience excessive serviceability problems?
• What risk or impact would such a collapse present to the traveling public or adjacent property?

Introducing an Asset Management System

A few agencies have developed ERS inventories that will allow them to begin systematic evaluations of their ERS network, develop improved design and construction details and inspection practices, develop strategies for maintenance and rehabilitation, and develop appropriate monitoring protocols to assess long-term behavior. The following are examples:

• The Oregon Department of Transportation (ODOT) is embarking on a retaining wall management program to inventory and assess the asset across the state. The agency is taking these measures because it has identified retaining walls as critical assets that could have significant consequences and risk if they fail.
• The City of Cincinnati has been using a retaining wall inventory and inspection system since 1990. The system allows the city to maintain a prioritized list of repairs and replacements based on regular inspections; in addition, the system helps the city respond rapidly to public concerns about its walls. The system currently tracks 6,796 retaining walls within the right-of-way, equivalent to approximately 159 miles in length, which includes privately owned walls that affect the right-of-way.
• The National Park Service (NPS) recently implemented an ERS asset management program. The NPS structures range in age from newly constructed to over 80 years old, with many showing signs of deterioration. These critical structures support park roads, as well as scenic vistas and overlooks. FHWA's Federal Lands Highway Division office is developing an inventory and condition assessment of all ERS associated with roadways and structures throughout the NPS park road system, including collecting data on location, number, size, condition, consequences of failure, and estimated cost of replacement or repair. This effort is designed to define and quantify the needs associated with these assets and to assist in developing a facility condition index for roadway assets.

Benefits of Including Earth Retaining Structures in Your Asset Management Plan

• Make more informed, cost-effective program decisions and optimize the use of existing highway funds and resources
• Maximize transportation system performance
• Simplify tracking of roadway asset locations
• Minimize life-cycle costs and maximize return on investment
• Measure and analyze performance of like assets
• Improve asset preservation through the use of focused preventive maintenance efforts

This article is a reprint of the Federal Highway Administration's publication no. FHWA-IF-08-014. Reprinted with permission.

Protecting the Future of Your Highway Infrastructure

Use the resources below to learn how to implement asset management techniques and data tools to protect your critical investment in Earth Retaining Structures (ERS), maintain public safety, and maximize maintenance funding.

Contact

Shyan-Yung Pan, P.E.
FHWA Office of Asset Management
202.366.1567
shyan.pan@dot.gov

Reports and Websites

• City of Cincinnati. "Retaining Walls and Landslides."
• Oregon Department of Transportation, "Retaining Walls Asset Management."
• Federal Highway Administration, "Asset Management."
• National Park Service Retaining Wall Inventory and Assessment Phase 1 Report, Federal Highway Administration, Federal Lands Highway Division, April 2005.
• Feasibility of a Management System for Retaining Walls and Sound Barriers (Report No. CDOT-DTD-R-2003-8), Colorado Department of Transportation, Research Branch, May 2003.

The UC Berkeley Transportation Library staff can help you locate these reports. Visit the ITS Library page for more information about the library or to make an inquiry.

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