Posted by: miniflex | February 19, 2010

Miniflex on burying Optical Fibre underground.

Best Practice article looking into the deployment of underground fibre.

Article originally published in OSP Magazine

I recently had a small epiphany watching my black lab Snowplow bury a bone in the backyard. Why did he do this? Because that bone was something precious to him and he wanted to protect it from any number of things that could cause him not to be able to use it in the future.

We actually could learn a lot from dogs. They choose to protect what is precious to them by using the safety of the earth. In a similar manner, we do the same for the valuable fiber we chose to install underground and wish to use in the future.

Historically, our nation’s respective networks have found safety in being protected by one medium: dirt. Now as we aim to deliver fiber-to-everywhere, we need to embrace this medium in a manner that allows us as an industry to protect this capital investment and create a manner to restore it in the rare occasion (I say that with tongue in cheek) when it is damaged.

Changes Revealed
The original manner we used to bury our facilities underground was to put a man on the end of a shovel and have him dig a trench as deep as reasonable in relation to the value of what we were protecting. The more valuable, the deeper it went. And the deeper it was, the more expensive the process became.

Now, as we aggressively deploy fiber to the end user, we must re-look and evaluate the methods by which we install it. In order to do this, let’s review four underground construction methods, and the pros and cons associated with each method.

Method A: Vibratory Plows
With the advent of vibratory plows, we moved a long way from the days of digging by hand. This technique minimally disrupts the soil and buries our precious cargo at a reasonable depth of 8-12 inches. Installing fiber at this depth provides moderate protection to the product while minimizing the damage to the customer’s property.

This efficient manner of installing, however, is only as good as we choose to make it. It relies on the operator to choose a path that is clear both on the surface and under the ground. The downside is that if the plow hits an immoveable object, it may require an excavation to remove the obstacle. And excavations are normally not included in a project’s original estimate.

Method B: Open Trenching
Open trenching is another installation method often used where joint-use trenches are allowed. (See Figure 1.) This provides a simple manner of installing multiple services underground while also keeping the costs down. The downside is there must be a clear path just as with the vibratory plow, and, if there’s not, any unanticipated obstacles can wreak havoc on the project’s cost structure. As we all know, any type of underground restoration can be very costly. That’s why this installation technique is a good solution for greenfield deployments.

Figure 1. Open trenching.

Method C: Directional Drilling
A high-tech method for installing fiber underground is directional drilling. This slant-nose technology was developed many years ago, and it is beneficial because it allows the operator to steer the boring head. This technique allows for very precise placement of the structure even around curves and obstacles.

Some time ago, I was able to witness this precision at a Horizontal Directional Drilling (HDD) rodeo where teams competed in placing the drill head inside an 8-inch donut some 200 feet away. The accuracy of this method is impressive. In addition, directional drilling results in very little or no disruption to the customer’s property while the fiber is being placed.

This tactic is effective in those brownfield installations where expensive landscaping and solid structures are in the way. The downside to this method is that it can be the most expensive method of installing fiber underground.

Method D: Micro Trenching
A less common underground construction method called Micro Trenching  is now being embraced for applications where the path for fiber installation is covered in a hard media such as concrete or pavement. It typically involves the use of a powered rotary saw that carves a trench normally only 1- to 2-inches wide and about 18 inches deep. Once the trench is carved, a microduct or a vertical cluster of microducts is installed into the trench. The trench is then filled with epoxy or a cold-patch.

This is normally used in those instances where there is no other manner to get to the end user. It is often a good alternative in alleys or large parking lots where the cost of directional drilling is prohibitive.

The width and depth of the vertical cut depends on whether the application is for backbone, access networks, or both.

An iteration of micro trenching is called FlatLiner. FlatLiner arranges the microducts in a stacked configuration. The configuration is then oversheathed to maintain that structure instead of the common round cluster configuration that positions the microduct with one in the center and all the others surrounding like numbers on a clock. This vertical configuration allows access to individual ducts by opening the sidewall of the oversheath once inside the handhole. This is a more user-friendly method than with traditional multiduct. Why? Because when trying to access a microduct that is in the center of the cluster, the technician must pry the outer ducts apart. This brings into play all sorts of issues as far as potential damage to the structures and working fibers in the cluster.

FlatLiner also allows for the deployment of more ducts in a smaller space. It is possible to place 2 stacks of 16 FlatLiner ducts side-by-side in a trench as small as 2 inches wide. That gives the end user 32 ducts in a very limited space.

Another tactic within micro trenching is called the ComboFlatLiner. This is where Backbone and Access tubes are combined in the same line. (See Figure 4.) It saves time, and allows a good soil compaction or fillers.

Figure 4. ComboFlatLiner is where Backbone and Access tubes are combined in the same line.

Interestingly, there is one common thread to each of these processes. They each force us to create a methodical process to installing underground facilities. Why is that necessary? Because for years conduits were encased in concrete and protected near the central office. They were also so well documented that anyone working in the area knew beyond a shadow of a doubt that something very important was under the ground.

Today, we must extend this principle into the outside plant with a similar level of protection through The Last Mile. If we plow, trench, bore, or micro trench a fiber into the ground without some methodical process, we have only provided for half of the equation. We have given our capital investment the protection of the earth, but we have done nothing to prepare for its restoration when there is a mishap. And let’s be honest, there are always mishaps.

With the advent of microducts, it has become easier to both deploy and restore these services. These small-diameter ducts allow us to use smaller machines during the deployment while providing fiber counts that will service the customer with all of those wonderful things they expect both today and into the future.

Lessons From the Old Dog
So, just as Snowplow goes back into the yard to find the bone he buried earlier, micro trenching allows us to return back into the same structure we once used to lovingly protect our capital investment. By using this technique we can easily locate and access our precious bone. Even better, we can use our valuable bone to deploy services that will set us apart from competitors trying to take our customer.

Let’s use the advances in the underground technology to the best of our abilities and give the customer what they truly want: a true future-proof network that is both protected and restorable.

Who says old dogs can’t teach us some pretty valuable tricks?

Scot Bohaychyk - Miniflex

About the Author
Scot Bohaychyk is the National Sales Manager (North America) for Miniflex. He has more than 25 years experience in Communications Cabling and Outside Plant Construction and Engineering. For more information please visit or

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