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An End to the Utility-Cut Bump? Micro Trenching Emerges as Kind to Pavement, Motorists

By February 21, 2011July 8th, 2014No Comments

The New York City Department of Transportation and motorists on Staten Island, New York experienced last fall what has become a common problem in an increasingly wired world: A utility cut was made to a recently repaved stretch of road. The cut was filled with temporary-patch asphalt, but it was deteriorating rapidly just weeks later – and drivers were not happy.

This has happened countless times in recent years, as businesses and residential areas demand greater access to broadband cable. DOTs and utility companies try to coordinate schedules to the effect that paving is done last, after the various utility lines are laid. But it doesn’t always work out that way. Paving and utility companies work on separate timetables for unrelated reasons.

But as a utility company in the Cayman Islands and its cable-installation contractor proved recently, there’s a smart way to work around this problem. It’s called micro trenching, which involves a narrow, almost imperceptible slit cut into the pavement to accommodate thin cables. It enables quick installation of the cable with minimal damage to the pavement.

Two innovations have enabled this streamlined approach to utility cable installation, which involves a cut less than an inch wide for a 12-inch-deep channel.

One technological advancement is with the cable itself, a “micro conduit” that has up to seven channels for seven wires, vertically stacked on top of each other instead of a rounder, fatter bundling as is found in traditional cable.

The second innovation is how the trench itself is cut. An air-cooled saw cuts the narrow trench to a width just wide enough to accommodate the stacked-up cable. To do this, an advanced blade manufacturing process provides a narrower blade that is just as strong as thicker blades. Traditional pavement cutters are cooled by water, which is a messy process that takes up more time in the clean up phase.

Less traffic disruption during and after under-pavement cable installation

Micro trenching might radically change this difficult marriage between utilities and pavement for the better. It’s faster, so there is less time spent holding up vehicular traffic on the roads where it is being used. While a relatively new process without a lot of experience on which to base a cost-analysis, it appears to be a less expensive process than with the four-inches-to-six-foot wide cuts that plague fast-moving vehicles. The pothole-like shocks to cars traveling over utility cuts are eliminated, as are the opportunities for new potholes to form.

One such micro trench was installed by Slimlines Trenching Ltd. in the Cayman Islands. The contractor was working for Logic, a voice-Internet-cable TV utility on the islands.

Richard Corbin, managing director for Slimlines Trenching, shared with us how the micro trenches were dug, why they are possible – and how these road cuts were later filled to avoid pavement deterioration and pothole formation further down the line. What are the dimensions – width and depth – that make up the micro trenches?

Corbin: We are currently cutting a .75” x 12” deep trench in the center of our capital and business district of George Town, Grand Cayman and have also cut .95” x 12” in some areas as well for the installation of two conduits which are placed side by side for increased capacity as required. I read that microtrenching about eight years ago was problematic, in part because the trenches weren’t as deep. What is new today that enables micro trenching to be workable?

Corbin: Advances in equipment and conduit manufacturing processes have enabled equipment manufactures the ability to scale down the size of the equipment and trenching attachments required. Advances in the blade manufacturing process enabled blades to be narrower while maintaining their strength, along with the use of high volume vacuum systems allowing the blades to be air cooled, therefore extending the life of the blade while eliminating the need for water cooling and the messy clean up and residue associated with the same.

Another improvement is the availability of micro-conduit, which is narrow and vertically rigid, along with advances in fiber technology, which have reduced the overall size of fiber. Is it about flat cables versus round? In our case it is more so about the conduit, with the conduit being narrow, flat and vertically rigid. It was perfectly suited for our customer’s needs. From a construction costs perspective, does the method compare favorably to traditional trench cuts?

Corbin: It is hard to say with certainty, but based on our experience and the feedback we are receiving it seems to compare favorably (this is the first trenching project we have been involved in – [there are many] variations in conditions and requirements involved in trenching). Micro-trenching has a considerably lower impact on the environment and is neighbor friendly, with minimal disruptions to vehicular and pedestrian traffic due to the reduced size of the required work zone. In some cases it requires only half a lane to be closed; reinstatement is completed simultaneously with the lane being reopened to traffic immediately following the reinstatement, which in most cases is a matter of two to three hours. You used cold mix asphalt for sealing. Is this a material you have worked with in the past?

Corbin: As mentioned above, this is the first microtrenching project we have been involved in. Therefore it is also the first time we used asphalt for reinstatement. However, based on our research the EZ Street cold patch was the product best suited to micro trenching and available for our needs and conditions (relating to the reinstatement of the narrow trench while satisfying the requirements of our local National Roads Authority). How was it to work with and did you find it preferable over a hot mix?

Corbin: We found the product consistent and easy to work with from the manageable 35-pound bag size. It almost creeps into the trench by itself, as it has a pliable nature and is easy to cleanup. Do the costs and performance features of microtrenching suggest easier, less expensive installation of cabling overall, that it might extend broadband and other services further and faster?

Corbin: Overall the micro-trenching process seems to be faster resulting in realized time savings. When delivering new services it can mean the difference between being first to market and third or fourth.

While there can be many factors that lead to roadway congestion and gridlock, construction-related projects is one of the major contributors to traffic tie-ups. As Slimlines Trenching illustrates, cutting down those times and spaces where lanes need to be blocked can reduce motorist inconvenience – and costs.

In a study conducted ten years ago, the Texas Transportation Institute determined that in the 75 largest metropolitan areas of the U.S., delays wasted $67.5 billion in lost worker productivity and 5.7 billion gallons of gasoline (21.6 billion liters) during 3.6 billion vehicle-hours of delays each year. Costs to individual drivers in such delays range from $200 per year in smaller cities to $1000 in more populous metro areas.

In other words, what’s good for reducing costs to utilities for cable installation is also good for municipalities and states that are responsible for pavement quality and pothole prevention. Motorists benefit in reduced traffic tie-ups during the construction, lower costs for car repair from pothole and utility cut damage to tires and axels – and, those motorists may get better and less expensive utility service, too.

Our bet is that there are residents of Staten Island in New York who would wholly support use of micro trenching in future cable installations.

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