The Proliferation of Microtrenching

There is an interesting new trend in fiber construction. Some relatively large cities are getting fiber networks using microtrenching. Just in the last week, I’ve seen announcements of plans to use microtrenching in cities like Mesa, Arizona, and Sarasota Springs, New York. In the past the technology was used for new fiber networks in Austin, Texas, San Antonia, Texas, and Charlotte, North Carolina.  I’ve seen recent proposals made to numerous cities to use microtrenching to build new fiber networks.

Microtrenching works by cutting a narrow cut an inch or two wide and up to a foot deep for the placement of fiber cables. The trench is then sealed with a special epoxy that is supposed to bind the hole to be as strong as before the cut.

Microtrenching got a bad name a few years back when Google Fiber walked away from a botched microtrenched network in Louisville, Kentucky. The microtrenching method used allowed water to seep into the narrow trenches, and the freezing and thawing during the winter caused the plugs and the fibers to heave from the small trenches. The vendors supporting the technology say they have solved the problems that surfaced in the Louisville debacle.

There is no doubt that microtrenching is faster than the more traditional method of boring and placing underground conduit. A recent article cited Ting as saying that a crew can microtrench 3,000 feet of fiber per day compared to 500 feet with traditional boring. Since a big part of the cost of building a network is labor, that can save a lot of money for fiber construction.

I’ve worked with cities that have major concerns about microtrenching. A microtrench cut is generally made in the street just a few inches from the curb. Cities worry since they have to routinely cut the streets in this same area to repair water leaks or to react to gas main leaks. In many cases, such repair cuts are made hurriedly, but even if they aren’t, it’s nearly impossible to dig down a few feet with a backhoe and not cut shallow fiber. This means a fiber outage every time a city or a utility makes such a cut in the street, with the outage likely lasting from a few days to a few weeks.

The bigger concern for cities is the durability of the microtrenched cuts. Even if the technology has improved, will the epoxy plug stay strong and intact for decades to come? Every city engineer gets nervous seeing anybody with plans to make cuts in fairly pristine city streets.

City engineers also get nervous when new infrastructure is placed at a depth they don’t consider as ideal. Most cities require that a fiber network be placed three feet or deeper below other utilities like water and gas. They understand how many cuts are made in streets every year, and they can foresee a lot of problems coming with a fiber network that gets regularly cut. City engineers do not want to be the ones constantly blamed for fiber outages.

There are new techniques that might make microtrenching less worrisome. In Sarasota Springs, New York, SiFi is microtrenching in the greenways – the space between the curb and the sidewalks. The company says it has a new technique to be able to feed fiber under and around tree roots without harming them, thus minimizing damage to tree while avoiding using the city streets. This construction method doesn’t sound as fast as microtrenching at full speed down a street, but it seems like a technique that would eliminate most of the worries of the civil engineers – assuming it really doesn’t kill all the trees.

It probably will take some years to find out in a given city if microtrenching was a good solution. The willingness to take a chance demonstrates how badly cities want fiber everywhere – after all, civil engineers are not known as risk takers. I have to imagine that in many cases that the decision to allow microtrenching is being approved by somebody other than the engineers.

The Pros and Cons of Microtrenching

The cost of laying fiber is still the most expensive part of bringing broadband to new places. There is a relatively new construction technique that is worth considering for fiber construction. While it’s been around for a few years, microtrenching is gaining in acceptance as a less expensive way to lay fiber.

Microtrenching involves digging a narrow trench of one to two inches wide and up to two foot deep. These trenches can then hold multiple conduits for fiber. The technique can be used on open highways and is most easily explained by this short video from Ditch Witch. There are also smaller units that can be used to cross sidewalks, parking lots and driveways.

There are a few cities that are now encouraging microtrenching. The first was New York City that adopted the technique in 2013 and which now requires it unless there is a good reason to use some other technique. San Francisco just proposed requiring the technique a few weeks ago for all future fiber construction there. Google used microtrenching in some of their city fiber builds like in Austin and Charlotte, and is trying to get cities like San Antonio to approve the technique.

The pros for this technique are significant, mostly dealing with cost. The alternative to microtrenching for traversing sidewalks, driveways and parking lots is boring. The boring technique involves digging a somewhat deep hole of 3 – 5 feet and then using equipment to bore sideways underneath the concrete. There is significant labor involved in the process and there is always a danger of hitting other utilities, particularly when boring away from public rights-of-ways. Google says that microtrenching is vastly more efficient in areas with urban sidewalks and that they can microtrench as many as 50 customers in the time it used to take to bore to one customer.

There are places where this might be the only sensible technique. For example, I have a client that wanted to pass through national forest roads to connect two parts of a fiber network. The Forest Service would not let them use any technique that would disturb the soil off of the paved asphalt. But perhaps they would have allowed microtrenching.

But there are certainly downsides. Probably the biggest downside is that the microtrenching is a lot shallower than other kinds of fiber construction. That certainly is going to present a problem in later years when it’s time to repave streets. Most city streets around the country are on 30 – 40 year replacement cycles. During that time they usually get repaved with asphalt a few times, but at the end of the cycle the old paving must be excavated and the process started over. That replacement process generally digs down anywhere from 18 inches to three feet depending upon local soil and substrate conditions. And that could mean digging up all of the microtrenching. The replacement lifecycle for streets is so long that it would be easy for future road construction crews to not understand the unusually narrow depths of the microtrenched fibers.

The same concerns apply to parking lots and sidewalks, although there is often less chance of these being completely excavated to any great depth for replacement purposes. But there is often more localized construction done to replace or bring gas, water or electric utilities and future work could more easily cut microtrenched fiber.

Most cities have specific expectations of various utilities. They expect different utilities to be at specified depths, and anything that falls outside these expectations is likely to cause problems in the long run. This means that any locality that allows microtrenching needs to make sure to create ordinances that allows for it and to change the rules for other utility work and road work to account for it.

Another practical issue for many ISPs considering the technique is that there are not a lot of contractors doing microtrenching today – and that might make it harder to find somebody who can do the work for you. But the potential cost savings for microtrenching are so large that it’s something that should be more regularly considered as part of any major fiber construction plan.