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Bridges & Structures


Abandoned Underground Mine Workshop


St. Louis, MO
August 17-19, 1998

Tom Lefchik, Assistant Bridge Engineer, FHWA, Columbus, Ohio


The first Abandoned Underground Mine Workshop was hosted last year by the Ohio Department of Transportation. We would like to thank Rick Ruegsegger of the Ohio DOT for coordinating the conference. Ohio felt the need for a system of inventorying, investigating, monitoring, and remediating abandoned underground mines when a 12-15' diameter hole opened up in the eastbound lanes of I-70 late one Saturday night. A manual was created which is in the process of being implemented. The purpose of the first workshop was to share this information with other states. There was a good exchange of information and a positive outcome. As a result of the first workshop, a team of states loosely formed to continue to share information so that work/research is not duplicated.

State DOTs attending the first workshop: Illinois, Kansas, Kentucky, Maryland, Missouri, New York, North Dakota, Ohio, Pennsylvania and Pennsylvania Turnpike.

There was an agreement to continue to share information on remediation methods and research. The goal of this group of states is to generate and disseminate information and to find means to share costs of research. Everyone will benefit from the cooperation of sharing research and research costs.

The second Abandoned Underground Mine Workshop was hosted by the Missouri Department of Transportation and was held in St. Louis, Missouri. Rick Ruegsegger sent out a questionnaire which was summarized and contains some excellent ideas on research, vendors, environmental investigation presentations, etc. The results were distributed and discussed at the second workshop. Topics discussed at this workshop included working on developing better communication between the states, working on disseminating information from various states, and cooperative research and funding.

Rick was the individual contacted when the hole opened up in Ohio and has been spearheading this project.

Presentation Summaries

Rick Ruegsegger, Special Projects Coordinator, Geotechnical Design Section, Ohio DOT

The awareness of mines under roadways increased dramatically with the collapse of I-70 in 1995. There was a realization that other states were also having similar problems. Rick came up with a suggestion to inventory sites with the existing information and do risk assessment with this information to determine where priorities should be directed. A manual of these procedures has been approved and will be printed in September. For all who wish to obtain copies, contact Rick Ruegsegger. The manual will be sold for the cost of printing.

There have been 4600 identified mine maps located in Ohio with an additional 1/3 unidentified. The hole that opened up in Ohio was 13' x 9' and about 9' deep. A drilling and grouting program was performed to repair the roadway. 1800 holes were drilled, 30,000 tons of sand, flyash, and cement were placed and 2000 feet of roadway was repaired using air rotary drilling and flyash grout injection. A criteria of 100' of cover was used as cut off for remediation on the interchange (best guess as of this point). The total cost of the project was 3.6 million dollars. Two lanes of bridges, full width, were constructed where two areas had large amounts of broken material. A word of caution -- when working in this kind of situation one can expect the unexpected because one action can and will cause another.

The process according to the ODOT Abandoned Underground Mine Inventory and Risk Assessment:

Sites are inventoried working with existing information and site investigations are performed. After identifying sites, a site risk assessment is done. The initial evaluation consists of: 1) site conditions and 2) public's exposure to conditions. A sorting tool is a list of sites by category with guidelines established to monitor sites. The purpose of the site evaluation is to categorize and
prioritize a high risk list (priority site investigations). There is a priority site list for each high risk group. Recommendations will be to remediate immediately or to defer remediation until later. Construction documents will then be developed.

Factors attributed to the I-70 job:

Geophysical -- GPR, electromagnetics, seismic refraction and microgravity.

USGS wrote a publication reporting what they did for Ohio and it is available titled US Geological Survey 1997, 97-4221 - Water Resources Investigations Report.

Allen Goodfield, Staff Engineering Geologist, Illinois DOT

The State of Illinois continues to build and rebuild bridges over mined out areas by modifying the
structure type.

Mined out areas existing in Illinois.
1) 158 over Norfolk Southern Railroad which has obvious sags in the roadway.
2) Joliett Road.

The topography is flat at this first location and it was noted that the vertical curve carrying the highway over the railroad was beginning to flatten out. The bridge was designed in the late 1950s and constructed in the early 1960s. Dual bridges called simple span bridges exist at this site. Spans are steel girder supporting a concrete deck. The bridge was checked out per suggestion and was found to be located over a mined out area and the bridge was designed accordingly. The concept was that with a simple span bridge and mined out sites you could probably jack it up and maintain your profile bridge. In this bridge, joints jammed beyond the task of jacking up and reestablishing. The State of Illinois has retained a design consultant to determine what can be done. The design consultant has retained a geotechnical consultant who elected to do a geophysical survey. Allen expressed his skepticism of the procedure thus far and is awaiting the results. The design consultant will eventually prepare a report with his recommendations for repair.

Joliett Road is located between two quarries. The quarry company made a "state approved" effort to put two tunnels under the roadway. A 200' x 200' x 100' deep rock excavation was made, called the "Glory Hole." Afterwards, distress in pavement was observed. Shear failures occurred in the Jersey barrier and the roadway was closed down. Inspections were made and the state hired both a rock mechanic professor and Woodward-Clyde, then turned over the instrumentation and investigation stage to the consultants. The quarry company installed steel I-beams and H-piles. They established a 3 sides reinforcing on 4' centers and behind grouting base of H-piles, back to rock face. Now shearing and deformation of this reinforcement tunnel lane is beginning to show. One can see where one-half inch movement has occurred. Major rock falls are present. A tremendous number of instrumentation devices were installed - incline bore holes inclinometers installed up to 400' deep. Monitoring was done during each blast and reported to quarry company. This is where the situation currently stands.

Possible solutions:
1) Sell the entire roadway (1 mile) to quarry company and make them pay for it and abandon the roadway - which would be politically incorrect.
2) Engineering solution that has been unofficially presented -- tie together the rock with rock tendons. This does not guarantee that stress will not continue to build up.

Bob Henthorne, Regional Geologist, Kansas DOT

Three types of mined areas in Kansas:

Gypsum Mines - are governed tightly and consequently there are not many problems with them.
Limestone Mines - The ones they did have problems with turned into cold storage units, etc. and are governed by their own safety factors (MSHA).
Salt Mines - Salt mines are mined by two different methods.
Solution method - water is dumped down one hole and dissolved salt is pumped back out another.
Room and pillar mines - similar to coal and limestone mines.

There is trouble with salt mines when oil fields are mixed in with salt mines -- the casing starts to leak, dissolves salt, and causes severe collapses.

One area referred to as the "I-70 speed bump" has a 6' drop within one-half mile. There is a new proposal to realign area 1/4 mile to north. They tried to fix I-70 salt mine by pumping bentonite grout in a series of 6 holes around the location of casing but there is a 2 to 3" drop per year with a 6' deformation in roadway.

Coal mines caused considerable problems. Room and pillar or strip mines. Room and pillar areas - grouted approximately five miles of underground mine works at a cost of 7 million dollars.

Successful method of repair: barrier wall holes drilled on 5' centers at roadway edge then infilled with high slump grout in the center. Drilled series of holes to check, found 4" biggest expanse of hole. Another good method used is support columns: drill on 15' centers and pump 4-6" slump down shoulder or roadway.

Another problem is lead and zinc mines. Three catastrophic collapses occurred on U.S. 66. These were repaired by digging out, backfilling, and repaving over the top. During one particular collapse, they drilled 260' and never found any solid material. A monitoring system was set up and they have had no problem since.

A new highway is to be built over the worst lead zinc opening in the state - 290' down - open expanse of 285 feet. Continuous for 600' along right-of-way. Solution that is being looked at for this site: reverse rock holding -, tying entire mass together (150') of this surface course over mine opening to withstand loads.

Geophysics - little experience or success regarding seismic in this area. No GPR work has been done at all to date.

Resistivity - problems with resistivity and delineating mine works is that most of mines can change from dry to completely saturated or there are problems with collapse areas.

Resistivity - problems with resistivity and delineating mine works is that most of mines can change from dry to completely saturated or there are problems with collapse areas.

Mined out areas are routinely solved by grouting. The Kansas DOT has grouted up to a 75 feet void.

Discussion of Summary of 10/23/97 Questionnaire

Do you agree in principle with the group definition, area of interest, goals, and expected benefits as described in the attached letter? (Yes/No/Thoughts)


If anyone has a good source of information to share with the group, send to Tom Lefchik or Rick Ruegsegger to disseminate.

Website is a good source of information. What types of shared research (investigation, research, etc.) do you suggest the group should consider? Please list any envisioned research and/or any subjects you feel merit research efforts.


A way is needed to determine how much needs to be filled. What volume of materials is needed -- quantity? We need a way of legitimately getting a camera down there to determine the current condition of the mine.

Site can be characterized by using the right equipment with qualified people to run the equipment.
More exposure and training is needed for all with the right tools.
Different methods of remediation, roof nailing, grouting.
We should concentrate on a better way to identify what research is needed and how to prioritize it among the states.
Someone needs to review all federal publications and research that has been done to provide a list of the existing research and publications and enable us to see what is needed, an initial bibliography. Tom Lefchik volunteered to do this.
We all need to be aware of which area each state is interested in pursuing so as not to duplicate efforts.
Before any state starts research, coordinate with others to be sure the research has not already been done.
A listing should be provided indicating what remedial treatments states have done for mined out areas. Two categories: Investigation, Mitigation.

Are you aware of any available vendor(s) who might be willing to demonstrate a form of available products, services, or technology if there was interest expressed by multiple states? If so, would you be willing to coordinate such a demonstration at a location in your state? If not, can you provide information regarding the(se) vendor(s)?


Have companies at workshops in order to be aware of what expertise is currently available and to get information on past jobs that have been done regarding remediation. There is an annual meeting of vendors/geophysics which includes field software demonstrations, days of lectures, short courses, etc. Richard Benson will send information on this meeting to Tom Lefchik and Tom will distribute to
other states.The mechanisms for group communication must be defined. What form(s) of communications would you prefer to see utilized for each state's information sharing/communications with the group (e-mail, Web site, "Chat Room" Web site, Newsletter, etc.)?


A mechanism for group communication is needed such as a newsletter, meeting every two years, a web page on the Internet, etc. Tom is working with his office to create a web site specifically for the purpose of sharing information within this group. Each state will have access to post their own information on this web site. Meetings are very helpful - how often should the meetings be held? Every two years? Possible topics/emphasis for future meetings: remediation methods monitoring methods inventory procedures geophysical methods and their uses specific design treatments A suggestion was made to alternate one year investigative and one year mitigation. A suggestion was made to focus on one topic with good solid information such as remediation and have longer presentations. A suggestion was made to focus on a combination of information in order to be informed of what all has been done since the states are only meeting every two years. A suggestion was made for a general report to be provided from each state on what is going on that is important to them. Suggestion made to have next meeting post-construction in the late fall to winter. A request was made for volunteers to start coordinating for the next meeting. There were no volunteers so this topic will be included in a questionnaire.Comment by Barry Berkovitz was that the best way to share information is through e-mail user groups. Barry is willing to set up a subgroup for this group. If everyone has an e-mail address he can add them to a user group. He felt that sharing is the key but some people do not have e-mail/Internet access and out-of-state travel for meetings has been a problem. This situation can be addressed by developing a short course under demo project NHI. If there is an interest within the group, Barry is willing to organize a training program specific to teaching how to use instruments and benefits and limitations, etc. Barry has offered to go to each state and provide this type of training.

If interested in this training, send an e-mail of request to Tom Lefchik. One e-mail from Tom to Barry with a list of requesters would be sufficient and Barry will then set up hands-on training.

This item will be included in a questionnaire for an interest response. During the recent ODOT workshop, the group discussed information sharing. Two forms of information sharing generally discussed or suggested by our conversations include:

Compilation of information.
Activity log.


Internet web site is a good source of information in finding out what other states have done, are going, plan to do. This is one of the most important elements.We would also like to establish a "Requests for Information" mechanism. This could be done on the FHWA web page, by e-mail, etc. What are your thoughts regarding this subject?


A Web page and e-mail were the two methods mentioned. All are encouraged to add e-mail addresses from list provided by Tim Newton to user group and then use them. Anyone without access to e-mail and Internet is encouraged to make an effort to get it with this as justification.Possible funding mechanisms which the group might utilize for mutual gain and economy might include:

Outside resources.
Cost sharing.
Pooled funds.


The group needs to identify possible outside sources of funding. The simplest way may be for each state to choose a research effort and spear head with their resources.None of us can afford to commit all of our time to this informational exchange. Perhaps volunteers from the various participating states will be needed to help coordinate funding and research, compile information and activities lists, etc. In the case of research or vendor demonstrations, etc. the state initiating or proposing the work could volunteer to coordinate the effort for the group. Do you have any other thoughts?


None. Do you have other ideas or comments?


Inquiry made to Tom Lefchik as to when Web site will be up and running. It is a matter of when funding is available. All will be notified by mail or e-mail when site is up and running. Some of the topics discussed will be included in a questionnaire to be sent out by Tim Newton along with the workshop summary.

Updated: 06/29/2015
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