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Paving in the Winter, Sinkholes in the Summer

Mon June 29, 2009 - Southeast Edition
Kerry Lynn Kirby

When contractors widening Interstate 65 in Shelby County, Ala., came to the job site June 1 after a big rain and discovered a sinkhole in the road’s path, they weren’t really surprised. After all, they were excavating on Oak Mountain, in a limestone area where the geological phenomenon is common.

The gaping depression at about mile 246.5, which encroached beneath the existing roadway, could have caused a significant delay for the roughly $78.46 million job, but due to forethought by the Alabama Department of Transportation (ALDOT), a budgetary item and a mitigation procedure for such problems were already in place.

“It was as simple as calling the experts to come and do the repair,” said Bo Burks, project manager for lead contractor Wiregrass Construction Company of Ariton, Ala.

There happened to be three lanes instead of the usual two lanes in that portion of the interstate, and this kept traffic moving through the project area while ALDOT dealt with the hole. ALDOT had to close only the lane adjacent to the hole to prevent vibration.

State geotechnical engineers inspected the sinkhole, and Chilton Contractors Inc., the excavating and grading subcontractor on the larger project, did the remediation work.

After an exploratory excavation, the lime sink was excavated approximately 35 ft. (10.7 m) deep, 10 ft. (3 m) wide and 20 ft. (6 m) long and plugged with rip rap and concrete.

“Other than affecting traffic, the sinkhole had very little impact on the project,” said Wiregrass Project Manager Jay Bryant.

Accounting for sinkholes in the contract isn’t the only way ALDOT has thought ahead, Burks said.

The job, which began Oct. 15, entails building one additional lane in each direction for immediate use from exit 247 (Valleydale Road) to Exit 242 (Shelby County 52), building retaining walls and bridge widening and raising.

But it also includes building another northbound and another southbound lane for future use. The extra lanes will not be used now, but they will be built so that just minimal work will convert them into traffic lanes when it’s deemed necessary. Burks praised ALDOT’s wisdom, saying that ALDOT was taking a more cost-effective route than just building to current need in the growing area.

Another example of ALDOT’s planning wisdom, Burks said, is the bridge work, which will raise some bridges enough to account for future clearance needs and not just what’s needed at present.

Alabama Bridge Builders is the main bridge subcontractor on the job and it will work on the four bridges included in the project.

One of them, which goes under CR 52, is being widened and raised.

That bridge is being raised 2 ft. (0.6 m), double what is needed for clearance now, to “make a little space for later,” Burks said.

The project also will improve traffic flow.

“The public should enjoy less congestion traveling through Oak Mountain State Park and heading to work,” Bryant said.

Based on ALDOT delay information for the area, he calculated the new lanes will save travelers 10 minutes of driving time.

The area is so heavily traveled now that the job contract restricts lane closures to nighttime only. It allows traffic to be shifted to different lanes in the day, but the total number of lanes open must remain the same as when the project started, except in emergencies like the sinkhole. If two lanes were open when the project started, at least two lanes must remain open during all daytime work, though it doesn’t have to be the same two lanes.

“Whatever’s there when we started, we’ve got to keep every day,” Burks said.

That meant all of the original work to shift traffic had to be done at night.

ALDOT wanted to get started right away on the job, but asphalt had to be put down to form an extra lane to shift traffic into, and asphalt requires specific weather conditions to settle properly. Because it was winter, temperature dips slowed down the project at the beginning.

“It took from October 15 to June 1 to get traffic shifted on the entire project,” he said.

During that time, crews were doing about 30 percent nightshift work, 70 percent dayshift work. Now, work is being done mostly during the day, with only occasional night shifts.

During the course of the project, nearly 200 prime and subcontractor employees will be involved.

In addition to Chilton Contractors and Alabama Bridge Builders, subcontractors on the job include: Alabama Traffic Systems of Birmingham, Ala., traffic control; A-1 Sealing Inc. of Richton, Miss., scoring bit pavement; Abramson LLC, barrier wall; Alabama Guardrail, guardrail; Brown’s Clearing, clear and grub; Charles E. Watts, G Treatment; Delta Ground Works, seeding, grassing and mulching; Gonzalez-Strength Inc., engineering; H&L Construction, safety barrier rail; Kelly Road Builders, planning; Material Services, edge drain; Ozark Striping, of Ozark, Ala., traffic stripe; Temple Electric Co. Inc., of Gadsden, Ala., electrical; Zaragoza and Harris Construction Co., of Alabaster, Ala., concrete; Russo Corporation, of Birmingham, drilling; Gilley Construction Co. Inc., of Manchester, Tenn., bridge; and B&A Contractors Inc., of Florence, Ala.

The job will require more than 570,000 tons (517,095 t) of stone and asphalt, as well as 256,000 cu. yd. (195,726 cu m) of earthmoving.

About 226,000 cu. yd. (6,400 cu m) of dirt will be moved onsite, with about 30,000 cu. yd. (22,937 cu m) of borrow brought in from offsite.

There are three asphalt pavers on the job, including an Ingersoll Rand Blaw-Knox purchased from Cowin Equipment Company and a Cedar Rapids paver from Joe Money Machinery Co.

Caterpillar equipment on the job, including a Cat 953 loader, a Cat 416 backhoe and a Cat grader, came from Thompson Tractor.

The job is about 16 percent complete and, despite the slower-than-desired pace of wintertime paving work, it should be completed on schedule and at or below budget.

It’s almost expected that more sinkholes will develop on the job, as contractors excavate over and through Oak Mountain, but if and when that occurs, they’ll use the same procedure as with the first, and don’t expect the holes to hurt the job timeline, Burks said. CEG

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