Eyes in the Sky, Boots on the Ground

Natasha F. Lombard, E.I.T. and William W. Byland, E.I.T.

As the popularity of unmanned aerial vehicles (UAV) skyrocket, so does their use in the engineering and construction industries. In recent years, the City of Houston has started using UAVs for its drinking water distribution system projects. Houston’s largest ever water infrastructure project, a series of 120-inch and 108-inch water lines collectively called the Northeast Transmission Line (NETL), is currently under construction. What better way to document the extensive, 16.5-mile project than from the air?

All thirteen segments of the NETL are in the construction phase, with four at substantial completion. With drone videos and aerial photographs, the City has a detailed month by month documentation of the project, and the technicalities of the construction progress are forever preserved.

The City has also employed drones on several other large diameter water line projects under construction, including a 72-inch that will weave its way through Houston’s Downtown and Midtown Districts, and on condition assessment projects of existing facilities.  Drones are being used to capture preconstruction conditions, track construction progress, and document milestones along the way in these large projects.

Preconstruction Conditions

Even though waterlines are buried infrastructure that wouldn’t seem to lend itself to UAV applications, construction affords ample opportunities for their use.  Before the trench is excavated for the waterline, numerous preconstruction efforts are required. These include clearing trees, demolishing buildings, relocating fences and signs, installing above-ground appurtenances in newly acquired City easements, and removing and replacing landscaping, ditches, and parking lots along the alignment. Because of the extensive impacts of these efforts on the surrounding area, it is important to capture the preexisting conditions to track site restoration at the end of the project.

To that end, miles of the Northeast Transmission Line’s alignment were documented in detail by UAVs. Accomplishing this from the ground would have required several field representatives making multiple full day site visits, walking the alignment, and photographing each easement dozens of times to capture all of the important details.

With a drone flying the alignment recording still photos and videos, the process was accomplished in a day. In addition to saving significant time and expenses, high-resolution images of entire parcels from the air provided a more complete picture than the limited perspectives possible from the ground.   

Tracking Progress

UAVs can also provide a better overview of construction progress for staff who aren’t able to make regular site visits. Photos from the ground can lack a sense of scale or can be confusing depending on the angle they are taken from. Aerial imagery, on the other hand, offers a complete picture of an entire area, with clearly visible landmarks to orient the viewer.

Over the course of a year and a half, a 3.9-acre plot of land, once covered in trees, was transformed into a new detention pond with a freshly asphalted, wrap-around drive. With the site being in the floodplain and impervious surface added, the detention pond was required for adequate runoff drainage. Before the pond could be constructed, this was the site of major construction activity for the NETL, including the installation of a 108-inch by 84-inch by 54-inch water line cross, four large-diameter butterfly valves, a 54-inch hot tap procedure on a live 66-inch water line, and a tunneling operation. Now, only the manholes at the surface give away the web of pipe beneath it. This huge effort was documented every step of the way with the drone, capturing each phase of the installation from the initial clearing and grubbing to the final paving over several months. The scale of construction on this site would have been impossible to convey from the ground. There was simply no way to show progress on both the huge benched pit and the adjacent tunnel shaft simultaneously, except from above.

Milestones

In addition to monitoring the overall progress of the project, UAVs are also an ideal vehicle for recording technical procedures. Major construction activities, such as hot tapping large-diameter water lines or installing interconnects, are difficult to show from the ground.

For example, during the summer of 2019, a drone was used to capture the entire hot tapping procedure of a live 66-inch water line. From the ground, the line of sight is interrupted by support beams, trench boxes and various other equipment, obstructing views of the operation.  Capturing the entire process from the ground would have required filming and switching from multiple angles. On the other hand, once the drone was positioned above the site, it allowed a clear view of the entire process.

This summer, an 84-inch gate valve was installed at an interconnection between the new 108-inch waterline and an existing 84-inch waterline. An enormous, 35-ton valve was delivered to site on the back of an 18-wheeler, as crews waited anxiously and crowded around the steel-shored shaft where it was to be installed by a sky-high crane. Hovering in position, the drone watched and recorded as the valve was carefully lifted from the truck, slowly swung around to the shaft, and, ever so delicately, lowered into position between the pipe pieces. Such an intricate procedure required complete precision and concentration until the valve was securely bolted in place. The drone captured the procedure from a unique perspective, allowing a view of the entire area as well as down into the shaft.

It was imperative to document these big milestones during the construction of Houston’s largest waterline. Drones can reposition around during these procedures, moving seamlessly from one perspective to another without getting in the way or putting a cameraman in jeopardy. Footage like this has become an efficient mechanism for communicating technical construction operations and is beneficial for staff/crew training.

Challenges

These benefits give drones a clear edge over filming from the ground, but they are not invulnerable. The drone pilot must carefully navigate the environment around the construction project. Documenting milestone moments requires filming from specific angles and can bring the UAV into close proximity of construction equipment. That proximity poses several obvious hazards to a UAV, including collision risks with heavy equipment or surrounding trees and powerlines.  Thankfully, the bulk of the footage captured by a drone, including capturing pre- and post-construction footage and tracking construction progress, can be achieved from relative safety high above a site. Even at altitude, there are hazards that still pose a risk to UAVs: airspace restrictions such as those surrounding Bush Intercontinental Airport or over downtown during major sporting events, electromagnetic interference from high-voltage transmission lines, thermal updrafts in major industrial areas, and even attacks by territorial hawks. To mitigate risks, the drone pilot needs to plan and be ready to take swift action.

All of these hazards and more can come into play in dense urban environments, such as the 72-inch waterline through Houston’s downtown area. Capturing footage of the construction progress there requires more than just careful navigation around structures. The pilot must also frequently reposition to ensure a strong signal to the drone and remain vigilant and avoid non-participants in the surrounding area.

Conclusion

Water and wastewater utilities around the country are increasingly looking at better ways to monitor their construction projects.  The advantages that UAVs offer such as capturing activities over vast distances, saving time and money, and communicating intricate technical processes make them an ideal solution. With drone technologies becoming more advanced every year, their potential applications for the utility industry are numerous.

Natasha F. Lombard, E.I.T, and William W. Byland, E.I.T are engineers at Lockwood, Andrews & Newnam, Inc. (LAN), a national planning, engineering, and program management firm. They can be reached at nflombard@lan-inc.com and wwbyland@lan-inc.com, respectively.