Earth Retaining Structures (ERS) are an often-overlooked but critical class of assets within the nation’s surface transportation network. The Federal Highway Administration estimates that each year the United States constructs in excess of 160 million square feet of permanent ERS; some 40 percent are on public road projects. Increasing use of ERS over the past two decades can be directly tied to increased urban development, increased demands for roadway capacity, and construction in terrain made increasingly difficult by development as well as natural profile and geology. It is not uncommon in recent highway construction for a single complex interchange to require several thousand square feet of ERS. Urban transit, rail, and other transportation modes often rely on ERS as well. These retaining structures typically are essential to a transportation project’s economically and politically feasible design and reliable long-term performance. Monitoring their condition and assessing needs for maintenance, repair, and rehabilitation require knowledge and experience. The failure of an ERS not only threatens lives and property, but also can seriously disrupt transportation.
Although the body of knowledge for ERS design and construction – spanning a broad spectrum of structure types and construction methods – is fairly mature, understanding of the aging and deterioration mechanics and the influence of maintenance activities, methods for routinely assessing ERS condition, and metrics for characterizing and forecasting in-service performance remains primitive. Research is needed to enable transportation agencies to manage their ERS assets effectively, as crucial elements of a transportation system.
The objectives of this research were (1) to review the state of practice for management of ERS in transportation systems, (2) to propose a framework for ERS management as a class of transportation system assets, and (3) to identify methods for assessing ERS condition and metrics for characterizing and forecasting in-service performance that agencies can use to apply the management framework.
The research team reviewed and assessed current practices for management of ERS, using published literature, communications with agency staff, and other sources of information. The survey of practices encompassed types of ERS managed (for example, cut walls, fill walls, buttresses, abutments, culvert head-walls, wing walls), assignment of responsibility within an agency for ERS inspection and maintenance, criteria for defining types of ERS, inventory data collection, condition assessments and their frequency, definitions of failure and operational risks, management strategies, and reporting practices. Based on this review and critical assessment of current practices, the researchers developed a guide for ERS-asset management. The guide is designed to inform state DOTs and others undertaking to develop ERS-asset inventories and implement asset-management principles and practices.
PRODUCT: The guide was delivered to the AASHTO Standing Committee on Highways and is available for download here. (1.8 Mb PDF file)