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|Federal Highway Administration > Publications > Public Roads > Vol. 66 · No. 6 > Avoiding Voids|
by Thomas E. Lefchik, L. Rick Ruegsegger, and Robert W. Henthorne
Abandoned mines jeopardize the transportation system and public safety, but States are addressing this underground threat.
What do coal miners in Quecreek, PA, coal slurry pond operators and residents in Inez, KY, and motorists on I-70 near Cambridge, OH, all have in common? The answer is unexpected and life-threatening encounters with abandoned underground mines.
On July 24, 2002, miners working in Quecreek, PA, were almost killed by a sudden breakthrough of water from an adjacent abandoned mine. Quick thinking and massive rescue efforts saved their lives.
October 11, 2000, in Inez, KY, residents living downstream from an impoundment for waste products from coal processing were endangered when the impoundment wastes suddenly burst into an unknown abandoned mine beneath the impoundment. The breakthrough released approximately 946 million liters (250 million gallons) of contaminated waters into the mine. The wastes flowed out of the mine into streams and rivers, temporarily raising water levels up to 1.5 meters (5 feet), polluting about 120 kilometers (75 miles) of streams, and shutting down water treatment plants for several days.
Motorists driving eastbound on I-70 near Cambridge, OH, on March 5, 1995, had to swerve to avoid a sinkhole in the middle of the highway when 3.7 meters (12 feet) of pavement suddenly collapsed into an abandoned underground mine. Three cars and a truck partially entered the hole, but fortunately only one person was injured. A portion of I-70 was closed completely for about 3.5 months for repairs.
In 1997, as a result of efforts following the I-70 collapse, the Federal Highway Administration (FHWA), nine States, and a turnpike authority collaborated to form the Interstate Technical Group on Abandoned Underground Mines (ITGAUM) to share information, experiences, and practices; research the problem of abandoned underground mines; and explore ways to use modern technologies to locate, assess, and repair the mines.
A Widespread Problem
Many States experience problems with mines beneath roadways. Mine collapses less spectacular than the I-70 collapse have resulted in fatalities.
A variety of marketable materials are mined in subsurface operations, including gypsum, salt, clay, iron ore, gold, lead, zinc, limestone, coal, and other minerals and metals. A repository of mine maps managed by the U.S. Department of the Interior, Office of Surface Mining Reclamation and Enforcement, contains maps for mines in 45 States. However, maps are not available for all mines, and consequently the number of States with mines is higher than 45. Many older mines simply were not mapped, or operations ceased prior to the time when the Bureau of Mines began requiring maps. Others were small mom-and-pop operations. And, sometimes, even where maps exist, they may be inaccurate or incomplete.
Underground abandoned mines represent an out-of-sight, out-of-mind situation," says Dr. Marc Bétournay, a senior scientist with Natural Resources Canada's CANMET Mining and Mineral Sciences Laboratory (MMSL). "They are a universal problem in Canada, Europe, the United States, and elsewhere because they are overgrown with vegetation on the surface or forgotten about as people familiar with the legacy of industrial activity move away from the properties."
Mines present a danger to the traveling public due to potential pavement collapses, sinkhole formations in the shoulder and side slopes, bridge and structure settlement, and slides from mine collapse or mine drainage.
The extent of the problem is reflected in the growth of ITGAUM. The group now includes FHWA, 15 States, a turnpike authority, a Canadian province, Natural Resources Canada, and the Federal Railroad Administration.
Wrestling with Mine Problems
A few examples demonstrate the extent and complexity of the difficulties facing transportation agencies.
The Pennsylvania Turnpike Commission is constructing 27 kilometers (17 miles) of new expressway in southwestern Pennsylvania. In designing and constructing the highway, the turnpike authority encountered multiple coal seams, mine fires, slurry impoundments up to 15 meters (50 feet) deep, active mines, mines in various collapse and deterioration states, acid drainages, mines at various depths from the roadway surfaces, inaccuracies in the mine maps, and mines near proposed bridge foundations.
A new roadway segment in Missouri goes through an area that was mined for lead and zinc from 1850 to 1950. Some of the encountered hazards included mine vents, shafts 60 meters (197 feet) deep, and pits 3 meters (10 feet) deep by 3 meters in diameter. Most of these features previously were filled with loose material and were not easy to locate.
Beginning with the I-70 collapse, the Ohio Department of Transportation (ODOT) performed eight mine repair projects in 8 years at a total cost of $26.1 million. ODOT made the repairs on mapped and unmapped mines, primarily along Interstates and freeways. The Ohio Department of Natural Resources estimates that the State has approximately 6,600 abandoned underground mines.
Other problems encountered by States include vertical shafts hundreds of feet deep, water-filled mines, inclined mined mineral seams that extend to the surface, and mines beneath existing bridge foundations. Added to the technical problems are environmental considerations such as acid drainages, bat habitats, and mining spoils.
Help Through Cooperation
After the mine collapse under I-70, ODOT developed a process for locating mine sites underlying highways and assessing their safety. The Manual for Abandoned Underground Mine Inventory and Risk Assessment documents the process. In 1999, FHWA published a similar document under the same title (Publication No. FHWA-IF-99-007).
During the development of the manual, ODOT contacted numerous State departments of transportation (DOTs) and other State and Federal agencies to determine what these agencies were doing to locate, investigate, rate, repair, and monitor sites where abandoned mines exist beneath roadways. Through ODOT's research, it quickly became evident that the States were wrestling with the same issues but not sharing their knowledge and experience effectively. The State personnel dealing with mine issues also have numerous other responsibilities and pressing issues. Consequently, they can expend only a limited effort on mine-related responsibilities.
To open a dialogue between Federal and State agencies, ODOT and FHWA hosted a workshop on September 16-18, 1997, in Columbus, OH. The discussions at the workshop resulted in a lively exchange of information. The success of the meeting inspired participants to continue their cooperation and information sharing by creating ITGAUM.
Participants agreed that the group would be composed of technically oriented individuals responsible for the remediation of underground mines beneath highways. Although the group would continue to exchange information individually and with other State and Federal agencies and private industry, participants agreed that the group could achieve its goals best with a focused membership.
ITGAUM's two primary goals are to generate and disseminate information, and obtain outside funding or cooperatively share in the costs of research or other related, mutually beneficial activities. By achieving these goals, ITGAUM members expect to increase the efficiency and effectiveness of each State's operations and enhance the safety of the traveling public.
In addition to sharing available information, the group, which meets biennially, also pursues activities to advance the state of the art. Members individually and cooperatively develop methods, technologies, processes, and management systems. The primary areas of focus are locating, inventorying, assessing, repairing, and monitoring highway and other transportation sites underlain by mines.
The technologies and methods used by ITGAUM also relate to other geotechnical and mining applications, such as looking for karsts (voids and caverns created by soluble limestone), locating abandoned mines in advance of mining operations, and trying to advance geophysics to improve subsurface investigations. The crossover of applications has led to information sharing among local, State, and Federal agencies, and foreign contacts.
For example, researchers studying the Quecreek, PA, and Inez, KY, incidents contacted members of ITGAUM to tap their expertise and experience. Also, Butte, MT, and State members of the National Association of Abandoned Mine Lands Programs requested copies of the Ohio and FHWA manuals to use as a model in developing risk assessment processes for residences underlain by mines. South Korea requested a copy of the manual as a model in their development of a similar process for roadways underlain by mines. A consultant in New Zealand requested technical advice on monitoring a road underlain by mines.
Nicholas Priznar, a transportation engineering geologist with the Arizona DOT, describes his experience participating in ITGAUM as "eye opening." Priznar points out that although States in the West have different rock types and generally smaller population densities concentrated near mining areas, the techniques for dealing with abandoned underground mines are the same as those in the East.
"From the papers presented at the workshops, I have learned a lot about effective strategies for detecting underground mines—such as site-specific geophysical investigations, effective subsurface boring methods, and records research—and how to approach making recommendations for mitigation," Priznar says. "Running into a hazardous abandoned mine structure when planning a new highway alignment in a western State may not occur as often as it does in eastern States, but it could turn into a big change order if a subsurface void is not detected until the project is under construction. Participating in ITGAUM helps civil engineers become familiar with mining techniques that might have an impact on civil engineering designs. Ultimately, greater understanding leads to more efficient and cost-effective construction."
ITGAUM has conducted four workshops. The first, the Ohio workshop in 1997, focused on procedures to inventory and assess sites. Attendees also discussed other aspects of the problem, such as methods for locating mine voids, monitoring sites, and remediating them.
Another workshop, hosted by the Missouri DOT in St. Louis, MO, took place in August 1998. This meeting focused on geophysical methods of investigation and monitoring.
At a Kansas City workshop in April 2000, the Kansas DOT opened the workshop with an afternoon of presentations by various participating transportation authorities. The balance of the workshop's presentations focused on investigating, monitoring, and repairing abandoned underground mines beneath roadways. Presenters discussed the roadway applications of geophysical techniques, such as the use of radar waves, electricity, vibrations, magnetic fields, and gravity to look underground. Special techniques and computer programs can be used with geophysical techniques to create three-dimensional images. All of the presentations included case studies demonstrating the application of the geophysical techniques.
The Kansas workshop revealed the need for cooperation and information sharing with individuals representing other modes of transportation, specifically railroads, that face similar problems with abandoned mine hazards. Consequently, the group agreed to invite representatives from a railroad organization to join the group. In addition, ITGAUM agreed to work more closely with other mine-related agencies and companies with experience using the same methods of monitoring, investigation, and remediation.
On May 1-3, 2002, the Iowa and Illinois DOTs jointly hosted the fourth workshop in Davenport, IA. This workshop included presentations regarding the modeling of stresses, strains, and failures of the rock in abandoned mines; geophysical methods of investigation; inventory and assessment; mapping; land use issues; and case histories.
According to geologist Matthew Trainum with the Iowa DOT, although mining operations in Iowa date back to the mid-1800s, the State has had limited experience in dealing with underground abandoned mines. But Trainum sees value in being proactive. "Our problems are not as immediate as those in other States where the threat of a mine collapse is common," he says. "But for us, it's a matter of locating the mines and determining if we might have a problem for future highway construction. That's why we became involved with ITGAUM. By keeping in touch and networking with States with more pressing needs for research and remediation, we hope to glean some insight into our own situation even though our needs today may be modest."
The Arizona DOT will host the next workshop in 2004.
Another means of generating and disseminating information is FHWA's interactive Web site at http://www.fhwa.dot.gov/engineering/geotech/hazards/mine/. The site features contact information for all members, a discussion board for group communication, summaries of completed workshops, a copy of ODOT's mine manual, and links to related Web sites.
A Transportation Research Board (TRB) special session, held at Rocky Gap State Park in Cumberland, MD, in May 2001, generated unprecedented attendance and interest in abandoned underground mines. TRB recognized the needs and interest in abandoned underground mines and created a Subcommittee on Abandoned Underground Mines.
The TRB subcommittee, ITGAUM, and FHWA jointly are pursuing several initiatives, including evaluating subsurface investigation methods, developing a manual of best practices, and refining modeling techniques for mine collapses. The subcommittee held its first meeting at the 2003 TRB conference in Washington, DC, and is planning its next meeting and a paper session for the 2004 TRB conference.
"Nobody should work in a vacuum," says Marc Bétournay of CANMET-MMSL. "The more information we have, the better we can analyze problems. From the development and refining of engineering methods, stability analyses, and modeling of mine behavior to the lending and borrowing of expensive equipment, sharing information can save time and help us ensure that we apply the right kind of solution to each situation."
Researchers expect the frequency of mine-related subsidence to increase as the mines age. However, ITGAUM members, FHWA, and the TRB subcommittee are working to improve efficiencies in locating, inventorying, assessing, repairing, and monitoring locations underlain by mines to improve the safety of the traveling public. The goal is no additional incidents like the I-70 sinkhole.
Thomas E. Lefchik is an assistant bridge engineer with FHWA's Ohio Division and is responsible for geotechnical matters. He has a bachelor's degree in civil engineering from the Pennsylvania State University, and he is a registered professional engineer in Illinois. Lefchik has worked in FHWA's Georgia, Illinois, Iowa, Kansas, Ohio, and West Virginia offices.
L. Rick Ruegsegger is the special projects coordinator for the Design Resource Section of ODOT's Office of Geotechnical Engineering. His current primary responsibility is to define and establish a statewide process for inventory and risk assessment of roadways above abandoned underground mines. His work for the State of Ohio since 1974 has included 3.5 years with the Ohio Environmental Protection Agency, 15 years with the Ohio Department of Natural Resources (ODNR), and 10 years with ODOT. His 15 years with ODNR involved project design and construction in the Abandoned Mine Lands Program of the Division of Mines and Reclamation. Ruegsegger has bachelor's degrees in civil engineering and biological sciences from The Ohio State University, and he is a registered professional engineer in Ohio.
Robert W. Henthorne is the chief geologist for the Kansas DOT. He is responsible for the supervision of geotechnical investigations conducted across the State. Henthorne received a B.S. in geology from the University of Kansas in 1983 and is a registered professional geologist in Kansas. He has worked for the Kansas DOT since 1984.
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