A Critical Component Tool in Maintaining Public Safety
Earth Retaining Structures (ERS) are often an overlooked critical component of America's surface transportation network. Each year, more than 160 million sq ft of permanent ERS are constructed in the United States. Current applications of ERS in highway projects accelerate construction, reduce costs, and enable the use of complex geometric designs. The use of ERS elements also enables vehicles to travel at increased speeds, reduces congestion, and lessens the environmental impact of highway and bridge construction. Ultimately, ERS serve as a vital tool in the successful movement of both people and goods across the country.
The current number of ERS used for transportation applications represents a significant 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. This network has expanded greatly during the past two decades due to increases in urban development, transportation capacity demands, and construction in complex and difficult terrain. 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's. 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 ft to more than 100 ft, are built to withstand significant technical demands and to resist very large forces. They frequently must be constructed in challenging site conditions, including mountainous terrain, soft ground, and sites that are below water. Some modern ERS systems require that engineered materials such as plastics, concrete, and steel be buried in harsh underground environments of soil and rock that may adversely influence the long-term engineering properties of the materials. 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.
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, ancillary structures, etc., to help ensure optimal usage of limited available funding.
These are just some of the questions that can be answered if your agency uses TAM techniques and data tools to inventory and evaluate its ERS networks and to start incorporating ERS in its asset management plan. An ERS management system can provide valuable information on the inventory, condition, maintenance needs, and performance of this important infrastructure asset.
As transportation agencies begin to recognize the importance of this asset investment, 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 a few examples:
To learn more about how your agency can begin to implement AM techniques and data tools to protect your critical investment in ERS, maintain public safety, and maximize maintenance funding, see the following resources. Make the most of your ERS investment and ensure the future of your vital highway infrastructure by finding out what TAM can do for you today.
Publication No. FHWA-IF-08-014