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 re- cent years, the City of Houston has started using UAVs for its drink- ing 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 cur- rently 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 wa- ter 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 prog- ress, 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 opportuni- ties 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 ease- ment 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 pos- sible from the ground.
108” x 84” x 54” Cross – Completed Detention Pond. Photo: LAN
108” x 84” x 54” Cross – Installation and Tunnel Shaft. Photo: LAN
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 cov- ered 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.
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csengineermag.com
december 2020
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