Drones have become an essential tool for monitoring construction progress and providing quality assurance. The ability to quickly and easily view what’s happening on a jobsite and share it with stakeholders has made drones one of the most widely adopted new technologies in construction. Advancements in camera and drone technology are also enabling new use cases.
Drone surveying
“I think it's generally true that anyone getting into drone surveying is doing more surveys than they expected to be doing,” says Rory San Miguel, CEO of Propeller, a provider of smart survey technology for the construction industry. Flights that were once completed monthly are now being completed every week, as clients find the data to be useful in planning their work. Using a drone with a GNSS receiver instead of a land-based rover allows users to scale the speed and frequency of surveys. Crews can survey a site in minutes as opposed to hours or days, without sacrificing accuracy.
Propeller helps clients, primarily survey teams for civil contractors, mines, and landfills, by getting them set up with the right drone technology and patented AeroPoints, high-precision, smart ground control points. Once pilots are trained and licensed to fly, drones can be used to collect detailed information on worksites from thousands of 2D aerial photos. GPS units on the drone, combined with the reliability of post-processed data, deliver survey-grade accuracy up to 3 cm.
“Our solution helps them survey their sites accurately,” says San Miguel. Within hours, using the science of photogrammetry, geotagged images are converted to highly accurate 3D maps of a worksite, useful in tracking and measuring every stage of a project. It can be used for stockpile measurements, road-grade checks, design conformance checks, and volumetrics.
Propeller’s post-processing kinematic (PPK) workflow takes the data that is collected during the drone flight and corrects it. San Miguel explains that the AeroPoint, with built-in dual-frequency GPS, serves as a base station to collect data from the ground while a flying drone collects data from overhead. Both sets of data are then uploaded and corrected to reach a survey-grade output.
“The main benefit of PPK vs real-time kinematic (RTK) processing is that there's no chance of a random signal drop out in the field,” says San Miguel. Drones equipped with LiDAR technology can offer even more precise measurements than cameras. LiDAR’s cloud point imagery provides a more accurate image of vegetation at ground level than traditional photogrammetry, which builds a 3D model over a photograph of the site. “Now you can fly over a heavily vegetated site and still capture the elevation under the ground cover,” says San Miguel. “That's going to help contractors in their bidding process even more than traditional images.”
Monitoring site progress
Skanska, one of the largest construction companies in the world, generally doesn’t use drones for precise surveys but instead uses them to capture a wide variety of data from its jobsites. They have a fleet of more than 50 drones and have 70 drone pilots on staff. “We’re not looking to replace surveying,” says Albert Zulps, Director of Emerging Technology at Skanska USA Building. “It's more like an efficient, fast way to get an overview of what's going on at your jobsite. A drone can capture a stockpile and using analysis software like Pix 4D, we can quickly extract an approximate volume.”
On most building projects Skanska will fly the same automated flight program on a monthly basis to capture before and after photographs. The information is primarily used by project teams but by storing all of the drone data in a cloud platform it becomes easier to share information with a variety of stakeholders, including project owners. “We found having a web-based, easily accessible, user-friendly platform has been the most important thing for us,” adds Zulps. “People share what they find in near real-time and that's been really important.”
Inspection
As a visual inspection tool, drones offer contractors increased safety and considerable savings by eliminating inspections from dangerous heights. Drones can hover over a specific area to check for problems and maneuver into places that human eyes would find it difficult to see.
“We flew a drone to inspect a bridge instead of building a scaffold and the cost savings were insane,” says Kara Fragola, a Field Engineer and Drone Pilot for Skanska USA’s Civil division. “The scaffolding would have been 10 times the cost of the drone flight.”
According to Fragola, “Some of the newer drones have features that allow you to zoom from far away and capture crisp images.”
Drones equipped with thermal cameras can check for water leaks or insulation issues. Thermal cameras work by detecting minute differences in heat on surfaces.
Some drones are also now able to fly indoors and in confined spaces, reducing the risk of conducting inspections in dangerous or difficult-to-reach areas.
Quality assurance
According to Zulps, drones can be used for quick-from-the-hip, quality control. “By placing scale images created by drone photogrammetry over an AutoCAD foundations drawing we can quickly tell if there is a mistake,” he says. “When we do these overlays with CAD, we're able to tie in exactly what we have with what we're supposed to have.” It’s an easy first step to identify an issue. Surveyors will then investigate further.
On earthmoving projects, drones can verify if the project was excavated to the right elevation. “It provides a paper trail of what work was completed,” says San Miguel.
Earthmoving contractors are also doing their own surveys to verify the accuracy of the plans they’ve been given. Based on the findings they can use this information to initiate a change order. This ensures they will be paid based on the actual dirt moved, not an erroneous survey.
Tips for flying safe
Skanska quickly recognized the value of flying drones in its operations and has had a drone program since 2015. Instead of hiring individuals whose only job is flying drones, Skanska pilots come from all walks of the company’s operation. In-house training ensures that the pilots are not only licensed but confident in their ability to fly a drone. “Now the training has developed into a drone community that mentors one another,” says Zulps.
An in-house flight staff gives Skanska the ability to deploy quickly when needed. Over the years they have learned to work with the FAA to obtain waivers when necessary and recently completed a flight over their project at Portland International Airport. However, when they need a drone with a unique capability or special flying skills are involved, they will outsource to meet their need. Here are some tips for safe flying from Zulps.
1. Don’t push it. For example, if you have a low battery warning, fly the drone back to the base and don’t risk extending the flight.
2. Give yourself a few days leeway to complete a planned flight. Wind, weather, and even last-minute visits by dignitaries flying into the air space could mean flight groundings and delays.
3. Be prepared to jump in. While most flights are automated you still need to be prepared to fly the drone manually. You never know when a bird might take interest in your drone, or when a lost GPS signal or interference can cause the drone to fly erratically.
4. Locate the highest object in your flight path, then plan to fly at least 50 feet above it. Check for things that may have changed on the jobsite since your last flight, such as the positioning of cranes.
