Small Trenches Bring Big Results

Microtrenching key to contractor's quick success

Slimlines Trenching purchased a Ditch Witch RT45 with MT12 microtrencher attachment (such as the one shown) specifically to install 17,000 ft. of fiber optic line through downtown George Town.
Slimlines Trenching purchased a Ditch Witch RT45 with MT12 microtrencher attachment (such as the one shown) specifically to install 17,000 ft. of fiber optic line through downtown George Town.

Slimlines Trenching entered the trenching business with a much narrower focus than most companies. The company is based in the Cayman Islands -- about 500 miles south of Miami in the Caribbean.

"There is a telecommunications company here that said it would like to provide infrastructure in the center of George Town in the business district," says Richard Corbin. But there was a moratorium on traditional trenching. "They had heard about microtrenching, but didn't have the expertise or anybody who had the time to fully research it, so I took that on as a project. We started Slimlines Trenching as a result."

Microtrenching cuts a narrow, shallow trench, typically from about 3/4 to 2 inches wide and to a maximum depth of about 12 inches. The intent is to trench just deep enough to get below the pavement, but shallow enough to stay above existing utilities.

Corbin purchased a Ditch Witch RT45 trencher with MT12 microtrencher attachment and an FX60 vacuum excavator. "The [telecom] made the commitment that they would do the job, so we made the commitment to purchase the equipment, hoping that down the road there would be future work for it," he says.

So far, that investment is paying off.

Advantages of a shallow trench

The project called for installing fiber optic cable in the heart of the bustling central business district in the island's capital. "It also happens to be where all the cruise ships tender. All of the tourists come ashore in George Town," Corbin points out.

In order to minimize disruption to traffic and local businesses, the installation took place at night.

"We put somewhere in the region of 17,000 feet [of conduit] in the ground in approximately four months," says Corbin. "We were only working four days a week, but they were about 12-hour days. It was all done at night, so as to get the efficiencies of little to no traffic and cooler temps."

Crews were trained on the microtrenching process as the project progressed. "Ditch Witch came down and did all of the training required. While they were here, we started cutting," says Corbin. "Our training was actually done hands on. We cut the trench that we were going to be using."

The project actually called for two cuts. "One was .75-inch wide and 12 inches deep, and that was about 13,000 feet," says Richard Corbin. The second cut, measuring .95-inch wide by 12 inches deep, made up the remainder of the footage, allowing for two conduits to be placed side by side for increased capacity.

"One of the reasons 12 inches was chosen -- not only by the infrastructure contractor, but the telecom and the National Roads Authority here -- is that all other utilities are deeper than 12 inches," he explains. "So crossings were not as much of an issue. There was reduced risk of interfering with or even severing any of the existing utilities."

It also provided maximum coverage for the conduit being installed. "It gave the telecom piece of mind that they had adequate coverage," says Corbin. "The conduit that we installed is 4 inches tall, so we ended up with 8 inches of cover. Any major road work that takes place normally would be only 4 to 6 inches deep."

Quick, easy restoration

Once the fiber optic line had been installed, sifted beach sand was used to fill the void between the conduit and the sidewall of the trench up to and slightly over the top of the conduit. The remainder of the trench - roughly 8 inches - was filled with EZ Street cold patch in a .25-inch aggregate size.

Approximately 3 to 4 inches of cold patch was placed in the trench per pass until the trench matched up to the road surface. "We had a custom packing wheel built for us that would fit down in the trench," Corbin comments. The manually propelled wheel weighs roughly 300 to 400 lbs. "The wheel can move up and down as you push it, so it's consistent. The weight is always applied down onto the material."

Restoration proceeded quickly, with minimal disruption to the surrounding community. Oftentimes, local business owners weren't even aware the installation had taken place.

"That was another reason that microtrenching was selected, because we were in and out at night. During the day, nobody knew we had been there," Corbin states. "I had business associates and friends of mine say, 'When are you coming down in front of our building?' and I would say, 'Well, we did that a week ago or two weeks ago.' They just didn't notice."

The project was started in November 2010 and completed in March. The restored pavement has held up well despite adverse conditions. "Since then, we've had a lot of rain and heavy traffic on all the roads and haven't seen a failure yet," says Corbin.

Moving on up

Since completing the initial microtrenching project, Slimlines Trenching has seen interest in the process from the other two telecommunications companies on the island. Corbin is also making plans to expand the company's services to traditional trenching from 4- to 12-inch widths and depths to 42 inches.

"Microtrenching led us into traditional trenching because we had enough people inquire with us as to what size trench we could do," says Corbin. "So we're expanding that way.

"Most companies start out with the bigger trench and go down to the smaller ones," he admits. "We're just doing it in reverse."

See Slimlines working this project on this EZ Street YouTube video.

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