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Federal Highway Administration Research and Technology
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|Publication Number: FHWA-HRT-09-003 Date: Mar/Apr 2009|
Publication Number: FHWA-HRT-09-003
Issue No: Vol. 72 No. 5
Date: Mar/Apr 2009
Maintaining slopes and restoring slopes, embankments, and roads after rock- and landslides is a major challenge with considerable impacts on State and Federal maintenance budgets. Slope failures and rockfall events disrupt traffic flow, damage public and private property, and cause serious safety hazards. The cost of restoring facilities back to a safe and functional condition is often much more expensive than prevention.
Each year, highway agencies in the United States spend millions of dollars maintaining highway embankments, slopes, and other earth structures; removing fallen rocks and debris from roadways; and repairing and restoring roads after slope failures. As the national focus shifts toward asset management and preserving existing infrastructure, the importance of maintaining embankments and cut slopes is more apparent. For this reason, the National Highway Institute (NHI) recently added a course on highway slope maintenance to its curriculum.
"Most of us have seen news footage of a landslide or mudflow impacting roads or homes, triggered by a large rain event, seasonal wet conditions, or flooding," says Benjamin Rivers, a geotechnical engineer with the Federal Highway Administration (FHWA). "Managing the conditions of slopes and their associated risks is the crux of this course."
A variety of routine maintenance activities can minimize the potential for slope failure. According to Rivers, routine slope maintenance activities should prevent conditions that promote erosion, deteriorate soil shear strength, or induce adverse loading. Because water is often the common denominator in all these conditions, controlling surface and ground water can prove effective in preventing slope failure in the long term.
In addition to understanding the role of maintenance in minimizing slope failures, highway personnel also should be able to recognize the telltale signs or mechanisms of instabilities, such as erosion, and the most effective means to mitigate potential problems, including routinely cleaning drainage ditches. Likewise, maintenance managers should have a systematic way to compare and prioritize competing slope maintenance needs.
|Shown here is a large retrogressive-type slope failure, which started as a small instability near the embankment toe.|
NHI developed the course Highway Slope Maintenance and Slide Restoration (FHWA-NHI-132081) for transportation field personnel. The instructor-led course, piloted in spring 2008, explains the conditions and factors affecting slope movement, stability, and deterioration, and the cost of maintenance and stabilization. The course also covers the rationale for slope management.
"This course bridges a gap between a department of transportation's maintenance workforce and management and geotechnical and geology staffs," says Rivers. "The intent is to provide field personnel with a fundamental knowledge of factors and conditions that affect the long-term stability and performance of slopes, and to provide best slope maintenance practices, slope stabilization and repair methods, and the fundamental aspects and considerations of managing slopes in relation to our roadway infrastructure assets."
Although the potential audience for the course includes geotechnical, operations, and asset management engineers, geologists, and others involved in assessing, maintaining, managing, and repairing slopes and associated features, the primary target audience is State maintenance workers. Course material does not cover highly technical content but explains key concepts in layman's terms with an asset management perspective.
|Proper maintenance and intervention with small slope instabilities, such as this one, can prevent larger, more costly problems.|
Upon completion of the 2.5-day course, participants will be able to discuss common soil and rock slope movement and instability, list factors and conditions under which slopes deteriorate, recognize common soil and rock slope stabilization techniques, and describe the key components of slope management systems. Instructors also underscore the importance of communication and coordination with geotechnical specialists.
Alicia Sindlinger is a contributing editor for Public Roads.