Lake Murray Back-up Dam Readies Area for Disaster

Thu July 07, 2005 - Southeast Edition
Jeff Cronin

At what was likely the biggest dam party of the year, South Carolina Electric and Gas officials June 23 dedicated a backup to the Saluda Dam at Lake Murray near Columbia, SC.

Crews from Barnard Construction of Bozeman, MT, have been at the site for three years to construct a backup dam to reinforce the original based on federal requirements for precautions against earthquakes.

In 1886, the Charleston area was hit with an earthquake estimated to have been between 7.1 and 7.3 on the Richter Scale, causing massive amounts of damage to the city and 60 deaths. Experts believe the area will get hit by a similar quake in the next 1,000 years and wanted to move ahead with the dam project.

If the Saluda Dam would have failed without the back-up, the resulting flood would have placed 120,000 people in danger and would have wiped out water supplied for the entire Columbia area.

Construction Manager Neil Van Amburg said the project, designed by Paul C. Rizzo and Associates of Monroeville, PA, brought with it all of the normal challenges.

Crews discovered the foundation had more irregularities than expected and a good number of crevices and ravines had to be filled.

“You never know what you’re going to find until you start digging,” he said.

In addition, more retaining walls than expected had to be constructed.

For the length of the contract, workers were on site 24/7, Van Amburg said, but, with the additional work that came up as the project progressed, they finished up just about on schedule.

However, the unexpected pieces added approximately 10 to 15 percent of the project’s cost, originally estimated at $250 million.

The nighttime work proved to be an advantageous time for roller compacted concrete (RCC) placement, which can’t be completed when the temperature of the RCC is above 65 degrees.

The use of RCC, while common on this type of project, called for the use of some unique equipment at the job site, Van Amburg said.

Crews used a creter crane, a Grove crane retrofitted with a telescoping conveyer, and a crawler placer, a retrofitted excavator, to place the RCC.

With these pieces of machinery, Barnard Construction entered the record books.

On Nov. 3 and 4, 2004, the crew set a world record for the amount of RCC placed in a 24-hour period. By the end of the day, they had set 18,600 cu. yds.

“We actually did set out to beat a record that day and were successful on our first attempt,” Van Amburg said.

The place at the top of the record book was short-lived, though. “My understanding is that it was broken somewhere overseas,” he said.

Barnard Construction workers also used a modified Cat 740 ejector truck to assist with the dam embankment.

Because of the nature of the work, South Carolina Electric and Gas (SCE&G) officials, based on the recommendations of an independent board of engineers, determined water levels had to be lowered during the early phases of the backup dam’s construction. In the fall of 2002, it was lowered to 345 ft.

At first, officials had expected the water level to remain at that level for up to two years, but, in response to the public’s concern, some aspects of the project were resequenced and, with the help of some significant rainfall, Lake Murray was up to its normal level after a year.

Van Amburg said Lake Murray is a huge resource to the surrounding community and “when people saw that the levels were going back to normal, they were relieved.”

The new structure stretches 1.5 mi. and consists mostly of rock excavated from SCE&G property downstream of the dam. The RCC portion sits in the dam’s mid-section.

Approximately 10 million tons of rock and concrete were used, all of which came from the on-site borrow area.

While the dedication ceremony has come and gone, Barnard crews won’t be gone for another few months. The dam is currently functional, but workers still have some grading and roadwork to complete, as well as some ash excavation.

At the peak of construction, more than 250 workers were kept busy on site. That number has since dwindled to 150.

Barnard has had a good core group of employees and was lucky to be able to find talent among local workers. However, “with that many people, you always have turnover issues.”

Van Amburg said they will likely turn the site over SCE&G in late August. That’s when the South Carolina Department of Transportation will begin work to complete the new stretch of Highway 6. Currently, the roadway’s two lanes run over the original Murray Dam.

As part of a 5.9-mi. project, two new northbound lanes will be constructed in between the dams and the two lanes on top of the Murray Dam will be reconstructed and become the southbound lanes.

Throughout the stretch of road away from the dam, crews will construct a fifth turning lane.

Construction costs for Highway 6, which includes three bridges, total $28 million, but SCDOT Program Manager Brian Keys said it’s just a part of a $125-million project that includes renovations to part of Highway 60 and some fill work in back of the dam.

C. Ray Mile Construction Co. in Elgin, SC, is the lead contractor for Highway 6.

Keys said part of the road project will already be completed for the C. Ray Mile crews before they gain access to the site. The SCE&G contractors will have ensured the earth has settled and “our contractor will come in and put the asphalt on top of the roadbed they’ve already built for us.”

To maintain the flow of traffic, the roads on top of the dam will remain open until the new northbound lanes are open. Then, the focus will shift to the current lanes. Keys said the current road was built overtop of concrete slabs, which will be removed and replaced with a stone and asphalt base.CEG

Caption:A conveyor system feeds the Cat 345 crawler placer.