The purpose of TDOT’s Rockfall Mitigation Program is to provide a continuing process for the evaluation and mitigation of rockfall problems along Tennessee roadways.
Given Tennessee’s terrain and the unpredictability of weather, aging of infrastructure and other factors, the threat of rockslides is ever present. Several years ago, TDOT began implementing a Rockfall Mitigation Program to address this issue. The program first identifies potential rockfall sites and then assigns a hazard rating to each location. The hazard rating is based on the potential for a rockfall event and the impacts to travelers and surrounding communities.KrjDWFggT7w
Rockfall Management System (RMS)
With an annual budget of approximately $2 million dollars, this program uses current resources such as the Rockfall Management System (RMS) developed by TDOT. This management system maintains an inventory of potential rockfall sites and gives each site a hazard rating. Through the use of a database and Geographic Information Systems (GIS) the RMS gives detailed information for each site. It allows TDOT geotechnical engineers, in cooperation with TDOT management, to prioritize, classify and compare potential problem sites. There are 232 priority sites and 949 “A” sites (the rating system assigns each site an A, B, or C rating representing a relative high, moderate or low hazard, respectively) statewide that could present a significant rockfall risk. Projects range from large scale installation of rockfall mitigation structures to hazard reductions based on cleaning up slopes and keeping rockfall catchment ditches clean. As of April 2012, the Department has successfully mitigated approximately 36 sites. Plans have been developed or are under development for an additional 8 sites.
The TDOT Rockfall Mitigation Program was featured in an article published in 2010 by Transportation Research: (http://onlinepubs.trb.org/onlinepubs/trnews/trnews266rpo.pdf)
The Rockfall Mitigation Program takes a positive, proactive approach to increase the safety of the traveling public. Funds from this program are prioritized according to the hazard and significance of potential rockfall sites as well as potential costs. Low cost, high hazard sites will receive a portion of the funding as will other high hazard sites that will affect large numbers of vehicles or have a negative impact on an area community.
This fund will not be able to repair all the rockfall sites that exist in Tennessee simultaneously. There are too many sites, some of which will be very expensive and many of which present environmental, traffic closure and property acquirement challenges. It will, however, focus on increasing the safety of the traveling public by addressing the problem with funding that continues on an annual basis.
In addition to the proactive approach of the Rockfall Mitigation Program, our geotechnical engineers and geologists will continue to rely on their partners in the TDOT Maintenance Division, who regularly monitor potential rockfall sites for changes in conditions. Should our maintenance field personnel notice a change in conditions that is cause for concern, they quickly notify the Geotechnical Office, and a geotechnical engineer or geologist is dispatched to the site where they will assess the problem and plan a solution. Maintenance forces have been proactive as well by addressing items within their scope of work such as scaling or removing loose rocks from slope areas and cleaning ditches in rockfall areas.
Projects Mitigated to Date
By 2005, TDOT developed a list of approximately 1,980 locations vulnerable to rockfall or rockslides. From that initial list, 36 sites were identified as highest scoring. In 2008, TDOT launched the first three projects to address these high priority areas. Since 2007, TDOT has contracted approximately $15 million dollars in rockfall mitigation projects.
Cocke County, I-40 Improvements
One of the first sites chosen for mitigation under the program was along I-40 in Cocke County near the North Carolina border. These cuts had been mitigated in the late 1980's, but several of the protection measures were showing damage and additional scaling needed to be performed.
Davidson County, I-440 Improvements
Two rock cuts sites along I-440 were improved in 2008 with the extensive scaling of slopes and installation of rockfall fence at the Hillsboro Road / I-440 On-Ramp and at the Murphy Road on Ramp. Several large falls at the Murphy Road site have been contained with the new rockfall fence.
Putnam County, I-40 Improvements
Eighteen separate sites were scaled and had problem boulders and overhangs removed. Rockfall fencing was added to a number to the sites to contain future rockfall where scaling, trimming and blasting could not sufficiently reduce the hazard without a fence. Over 1.6 miles of rockfall fence was installed.
Emergency Rockslide response: November 2009 – April 2012
Multiple sites in Polk, Sevier and Blount Counties failed during the winter of 2009/2010. While these sites such as US 64 in Polk County were not mitigated under TDOT’s annual Rockfall Program, these sites were on the statewide rockfall management system and geotechnical staff from TDOT’s Geotechnical Engineering Section work on both rockfall program sites and on rockfall/rockslide emergency response. Heavy winter rains caused numerous rockslides over this winter period, including the large slide along I-40 in North Carolina. In addition to these efforts, TDOT Maintenance has taken on smaller scale projects for rockfall hazard reduction including scaling slopes and cleaning out rockfall catchment ditches. Sites have been mitigated statewide in Blount, Campbell, Cocke, Davidson, Loudon, Marion, Polk, Putnam and Sevier Counties.
One early project was located along I-40 in Cocke County, just four miles west of the rockslide that closed the interstate in North Carolina in late October 2009.
Plans have been developed for Rockfall mitigation along a section of SR-16 southeast of Winchester, Tenn. Recommendations for mitigation include scaling of loose rock and vegetation, re-cutting sections of the existing rock cut and placement of a berm between the roadway and the completed rock face, shotcrete over shale zones and adding two rock buttresses. It is expected that a contract will be let in 2012.
Emergency Rockfall Response on February 20, 2011
Just after midnight on February 20, 2011 a massive rockfall closed SR-108 in Grundy County. An emergency contract was let in March that included shotcrete face treatment, installing a rockfall fence and a portable barrier rail. The work was completed in April of 2011.
Rockfall along I-24 Westbound in Marion County
In November 2010 and the last week of December 2011, there were three occurrences of rockfall along a stretch of I-24 westbound that resulted in the cutting of some vehicle tires but no injuries. Fortunately, one site (below @ LM 140.1) has a very wide catchment area; Region 2 Maintenance added a berm as an extra precaution to improve safety at this location.
In the long term, this site as well as others location on I-24 along Monteagle Mountain, will need to be included as a project under the TDOT Rockfall Mitigation program. However, additional design and study are needed to come up with a cost effective solution that has minimum impact on traffic and meets the needs for additional safety improvements. This will likely involve some combination of blasting, scaling,shotcrete wallinstallation and a protective berm and/or fence. There are 24 “A” rockfall sites along I-24 at Monteagle Mountain. Many of these sites may require extensive disruption to traffic in order to complete the rockfall mitigation.
There are no guarantees against the natural forces that can lead to rockfall events, but TDOT isn’t waiting for rockslides to make headlines. Our approach will remain proactive and aggressive. We will continue to monitor these areas, initiate preventative maintenance and projects, and dedicate the funds necessary to keep Tennesseans safe on our roadways.