SR-32 Sinkhole RepairClaiborne County

Report - March 2010EME

RE: Sinkhole Repair, SR-32 Claiborne County Dear Mr. Bowers: This letter report documents the work performed along State Route 32 from March 8 to March 11, 2010 in Claiborne County, TN.

Background EME conducted a soil/rock stabilization effort as well as a soil/rock removal effort from the stream in Hyberry Hollow in January, 2010. On January 20th , during a heavy rainfall, muddy water began flowing through our project from up stream. At that point you called personnel from CEC who were conducting maintenance further upstream to ask if they had caused the sediment release, and were told by CEC that the sediment was coming from upstream of their work, from Spring # 1 at the head of the stream. CEC later informed us that new sinkholes had developed in the side of the high road cut at the head of Hyberry Hollow, and that no sediment had ever come from Spring # 1 until these sinkholes developed. The next day, January 21st, Greg Russell was on site to inspect our work and he was shown these sink holes and agreed that they would have to be dealt with.

January 24th Inspection On February 24th, you, Doug Miller, and I were on site to inspect our January stabilization and clean-out work after recent rains. While in the area we decided to take a look at the sinkholes to see what progress had been made in repairing the sinkholes. At that point we discovered that no efforts had been made to repair the sinkholes.

At the foot of the hill below the sink holes we found Jonathan Debusk of TDOT along with a TDOT contractor installing a 24 inch corrugated metal pipe under the old SR-32. At this point you asked Jonathan what the plans were for repairing the sinkholes. Jonathan responded that he was waiting on a report from Geology, but that unofficially the word was they were not planning to do anything as the sinkholes were far enough from the road not to be a threat. Jonathan also said that he had been told that the sinkholes were “vents” to the caves and that if we repaired the sinkholes, new “vents” would form. Jonathan also stated that the sinkholes were on the side of the hill and couldn’t catch much water, and so they shouldn’t cause a problem.

Our inspection of the sinkholes revealed that the largest sinkhole was on the edge of a bench cut in the hillside which apparently catches runoff for a fairly large area and drains directly to the sinkhole. It was our opinion that unless these sinkholes were repaired they would continue to grow with time and that the material that collapses into the sinkholes apparently is flushed out through Spring # 1.

March Work EME and Viking mobilized to the site on Monday, March 8, 2010. EME provided geologic, engineering, and construction oversight services while Viking provided construction services. All of the work on site was accomplished with a medium sized tracked excavator. The road cut in which the sinkholes were located is bisected by three horizontal benches, and the sinkholes were scattered across the three benches in a line apparently caused by a geologic feature of some sort. A ramp was constructed to allow access to the middle bench and construction materials (rock and clay) were stockpiled on this middle bench. Materials were ferried up and down to the other benches/sinkholes with the excavator. An effort was made to restrict the excavator traffic to as small an area as possible to reduce the disturbance of established vegetation on the steep hillside.

The sinkholes were numbered while on site for reference while working. Sinkholes #1, #2, and #3 were located at the top of the slope, just below the upper bench. Sinkhole #4 was located just below the middle bench, and #5 was located on the edge of the lower bench. Due to the threat of rain, which would have made reaching the upper and lower sinkholes very difficult, the upper (1, 2, and 3) and lower (5) sinkhole were repaired first then the sinkhole on the edge of the middle bench (4) was repaired last.

Sinkhole #1 required no excavation as the bedrock throat was well exposed. Sinkholes 2, 3, and 5 were excavated down to apparently competent bedrock with a very well defined throat exposed in sinkholes 2 and 3, with a bigger, less well defined throat exposed in sinkhole 5. Bedrock was never reached in sinkhole 4, although very wet, weak soils were reached and removed. Depths to the top of bedrock/throat openings ranged from 4 - 5 feet in sinkholes 2 and 3 to over 10 feet in sinkhole 5. The maximum depth reached in any of the holes was 15 feet in sinkholes 4 and 5, at which point the throat constricted to the point that the excavator bucket was too wide to reach deeper in sinkhole 5 and we could reach no deeper in sinkhole 4 due to the angle of the hillside.

Once the throats were cleaned out as best as possible, or in the case of sinkhole 4 as much weak soil was removed as possible, the throats were filled with rock of a sufficient size to form a bridge across the throat. Once the throats were bridged, then progressively smaller rock was used to fill the holes to within 2 – 4 feet of the ground surface. Geotextile fabric was then placed over the rock fill and the remainder of the holes filled with compacted clay.

After the sinkholes were repaired, the areas disturbed by digging or excavator/truck traffic were repaired. These areas were repaired by seeding and covering with either straw matting or loose straw. Materials used on site included 5 loads of rock, 5 loads of clay, 17 rolls of straw matting, and 10 bails of straw. The attached photographs depict the work at this site. Please call me at 615.498-1066 or email at thughes@emetn.com if you have any questions regarding this matter.

ENVIRONMENTAL MANAGEMENT AND ENGINEERING, INC. Todd Hughes, P.G. Encl. Photographic Documentation

Photograph 1. SR-32 Sinkholes Excavation began on 3/8/10 at the upper most sinkhole.

Photograph 2. SR-32 Sinkholes Several large rocks were removed during excavation of the sinkholes. These rocks all showed solution features indicative of ground water movement at these locations.

Photograph 3. SR-32 Sinkholes. Two loads of rock were brought in initially to construct an access ramp for trucks to deliver material closer to the work area.

Photograph 4. SR-32 Sinkholes. Large rock used for repairing the sinkholes was delivered as close as possible to the sinkholes. The excavator had to transport the rock up or down the slope to each sinkhole.

Photograph 5. SR-32 Sinkholes. After each sinkhole was over excavated, large rock was placed in the excavation to bridge the opening.

Photograph 6. SR-32 Sinkholes. Geotextile material was used to cover the rock prior to compacting clay up to grade.

Photograph 7. SR-32 Sinkholes. Clay brought in from offsite was compacted on top of the geotextile.

Photograph 8. SR-32 Sinkholes. Each sinkhole was graded with a slight mound to allow for any potential settling, and to divert water away from the area. Areas should be inspected periodically to determine if additional cover is required.

Photograph 9. SR-32 Sinkholes. Disturbed areas were seeded and covered with straw matting.