RESEARCH PAY S O F F
Developing and Implementing
a Rockfall Management System
and Mitigation Program
for Tennessee
VA N E S S A C . B AT E M A N
A
s rock cuts along Interstates and high- agency therefore needs a systematic way to manage
The author is Civil
Engineering Manager, ways age, weather, and become unsta- the hazards of rockfalls.
Tennessee Department of ble, the risk of rockfall increases. Many
Transportation, rock cuts owned by transportation Problem
Nashville, and chairs the agencies were built before the development of Rockfall management at the Tennessee Department
TRB Exploration and design standards for rockfall catchment. Con- of Transportation (DOT) historically was reactive—
Classification of Earth sequently, many rock cuts have inadequate or that is, rockfall maintenance problems and cata-
Materials Committee. nonexistent catchment areas. A transportation strophic failures drove the remediation responses
(1). This haphazard approach did not make the best
PHOTO: HARRY MOORE
use of resources, and no mechanism was in place to
approach the problem on a statewide basis.
Rockfall sites could not be compared within or
across maintenance districts, and no map showed
all sites statewide. Tennessee had an unknown num-
ber of problem sites that presented an unknown level
of hazard; moreover, the state had no systematic pro-
gram to rate the hazards, to estimate costs, or to let
mitigation projects.
Solution
Multidisciplinary Approach
Tennessee therefore initiated a research project to
develop a hazard rating system for the state and to
produce a statewide map of sites. A rockfall database
integrated into web-based geographic information
systems (GIS) was developed to display, analyze, and
prioritize rockfall hazards. Researchers developed
field data collection forms, both paper and electronic,
which linked to the rockfall database via PDAs—
TR NEWS 266 JANUARY–FEBRUARY 2010
that is, handheld mobile computers. Tennessee DOT
developed a training program and manuals to assist
geotechnical personnel in implementing the system.
Principal investigators from Tennessee DOT, the
University of Tennessee, and Virginia Tech led the
multidisciplinary research team, which had back-
grounds in civil engineering, geological engineering,
Rockfall mitigation work in progress—workers assess
a site in Cocke County, Tennessee, for initial
vegetation removal and scaling operations.
Tennessee DOT has moved from a reactive to a
proactive approach to rockfall management. 35
and geology. The team developed the initial hazard tial disruption to traffic, roadway blockage time,
rating system and database, piloted it in five counties, length of the detour around the blockage, and facil-
and then refined the rating system, field procedures, ity degradation.
and database before mapping the rest of the state.
Photologs from the Tennessee DOT Roadway Applications
Information Management System made possible a In 2008, Tennessee DOT used the rockfall hazard
virtual driving tour along every mile of state road- inventory, database, GIS map, photographs, and
ways, looking for potentially hazardous rock cuts. other data to launch a rockfall mitigation program.
Potential sites were noted and verified in the field, The following sites with high scores on the Ten-
and new sites were added during the field work (2). nessee RHRS, high RCI scores, and high assessments
of mitigation costs were let in three contracts:
Rating Sites
Initially, sites were rated as A, B, or C according to the u The first contract, for $780,000, was to miti-
Rockfall Hazard Rating System (RHRS) developed gate 0.3 mile of highway in Campbell County, where
for Oregon DOT and the Federal Highway Adminis- a rockfall recently had occurred on I-75. Mitigation
tration (3, 4). At A-sites, a rockfall has a high poten- measures involved the installation of a rockfall fence
tial for reaching the roadway and affecting traffic; at the base of the slope on the edge of the paved
B-sites have a moderate potential hazard; and C-sites shoulder.
have a low potential hazard. u The second contract, for $1.2 million, was to
All A- and B-sites were located. All A-sites were mitigate 0.5 mile of I-40 in Cocke County near the
further analyzed with the Tennessee RHRS, which North Carolina border. Mitigation measures involved
produces a detailed hazard rating. The Tennessee the installation of a rockfall fence, draped wire mesh,
RHRS includes identification of the rockfall failure and a hybrid wire mesh system to reduce signifi-
modes expected at a site, such as planar, wedge, top- cantly the risk of a rockfall impacting traffic.
ple, differential weathering, or raveling. The Ten- u The third contract, for $537,000, was to miti-
nessee RHRS also requires such data as cut height gate 0.65 mile of I-440 in Nashville in Davidson
and length, average daily traffic, roadway width, deci- County. Mitigation measures involved scaling and
sion sight distance, rockfall history, ditch effective- trimming the slope to remove loose, overhanging,
ness, presence of water, geologic failure mode, and and unstable rock; cleaning and regrading the catch-
the extent of the potential failure area, expressed as ment ditch; and installing a rockfall fence as needed.
a percentage of the slope surface area.
All of this information determines the Tennessee Benefits
RHRS score, which has a maximum of 800 points. The three-year research effort cost $1 million in addi-
Sites with a score above 350 are classified as priority. tion to the routine work related to rockfalls.
Of the 1,950 sites statewide, almost half—963 sites— Although it is too early yet to quantify the financial
were classified as A and received a Tennessee RHRS benefits of the research, recovering the investment
analysis (Figure 1, below). Thirty-six of the A-sites and savings is a realistic expectation, based on past
were rated high priority, with scores of 500 or more. experience of road closures, property damage, fatal-
FIGURE 1 Rockfall sites in
After the initial research was complete, Tennessee ities, and inconvenience to motorists.
Tennessee: state routes, DOT added a Rockfall Closure Impact (RCI) rating The Rockfall Management System has allowed
U.S. highways, and and initial cost assessments for the sites. The RCI Tennessee DOT to approach rockfall issues as a
Interstates. rates a site according to average daily traffic, poten- statewide problem and to apply resources in a ratio-
TR NEWS 266 JANUARY–FEBRUARY 2010
36
nal way. Personnel can compare
PHOTO: HARRY MOORE
Scaling and vegetation
the hazard ratings of sites, the removal in progress at
costs of mitigation, and the the Cocke County rockfall
site.
potential effects on the travel-
ing public. Tennessee DOT has
expanded the results from the
research to incorporate prelim-
inary cost estimates and RCI
scores; along with the Ten-
nessee RHRS scores, these con-
stitute the selection criteria for
prioritizing mitigation projects.
With the interactive maps,
Tennessee DOT personnel can
display site data according to a
variety of criteria and can add
or modify sites as conditions
change. The database informa-
tion about rockfall sites is
updated periodically and as
needed. The database gives
Tennessee DOT staff instant
access to all data, photographs,
Tennessee RHRS scores, and
related reports before mobiliz-
ing to a rockfall site.
The GIS maps clearly iden-
tify areas within corridors that
have a high concentration of
rockfall sites. This information
is valuable in the cost–benefit
analyses for roadway widening,
improvements, or relocations.
Tennessee DOT plans to
expand the database and web-
based GIS to other geohazards
such as sinkholes, landslides,
and settlement areas, and to store the electronic data Final Report—Phase II. Tennessee Department of Trans-
and the interactive map in a central location. The portation, Nashville, 2005. www.tdot.state.tn.us/long
range/reports/res1189.pdf.
statewide map and system developed under this 3. Pierson, L., S. Davis, and R. Van Vickle. Rockfall Hazard
research project have allowed Tennessee DOT to Rating System Implementation Manual. Report FHWA-OR-
implement a new management program and to EG-90-01, Federal Highway Administration, Washington,
improve tools, enhancing staff efficiency and ensur- D.C., 1990.
TR NEWS 266 JANUARY–FEBRUARY 2010
ing safer roadways for motorists. 4. Pierson, L., and R. Van Vickle. Rockfall Hazard Rating Sys-
tem—Participant’s Manual. Report FHWA-SA-93-057, Fed-
For more information, contact Vanessa C. Bateman, eral Highway Administration, Washington, D.C., August
Civil Engineering Manager, 6601 Centennial Boule- 1993.
vard, Nashville, TN 37243-0360 (615-350-4133;
Vanessa.bateman@state.tn.us). EDITOR’S NOTE: Appreciation is expressed to G. P.
Jayaprakash, Transportation Research Board, for his
References efforts in developing this article.
1. Moore, H. L. Wedge Failures Along Tennessee Highways in
the Appalachian Region: Their Occurrence and Correc- Suggestions for “Research Pays Off” topics are welcome.
tion. Bulletin of the Association of Engineering Geologists, Contact G. P. Jayaprakash, Transportation Research Board,
Vol. 23, No. 4, 1986, pp. 441–460. Keck 488, 500 Fifth Street, NW, Washington, DC 20001
2. Drumm, E. C., M. Mauldon, W. M. Dunne, V. C. Bateman, (202-334-2952; gjayaprakash@nas.edu).
and B. McCarter. Rockfall Management System for Tennessee: 37
