Drones at the construction site: how to control the progress of work using BIM?

"Brasfield & Gorrie, one of the largest private construction companies, is using drone-derived 3D models to compare actual excavation work at a construction site with planned performance.

According to this year's Goldman Sachs report, the construction sector will see the greatest use of drones in the near future. We saw a similar trend when we analyzed user data in the DroneDeploy system for the "Drone Use in Industry and Commerce" report - the construction sector saw the fastest growth in drone use.

This did not surprise many people. Commercial and custom drone models today can easily fly over a construction area and quickly show the progress of construction on high-resolution maps and three-dimensional models, which is a very effective solution compared to traditional methods. However, despite frequent discussions of the benefits of using drones in the construction industry, there are not many real stories from construction companies that actually use them.

So we would like to present a story from Brasfield & Gorrie, one of the largest private players in the U.S. construction industry, about using drones, in this case to get an elevation map for a hospital and compare it with the construction plan to evaluate the performance of the work.

Drones at Brasfield & Gorrie

"Brasfield & Gorrie began using drones for surveillance several years ago, but had to temporarily stop due to the need to obtain approval under new regulations issued by the FAA on December 15, 2015. Today, the company's drone work is handled by the Virtual Design and Construction (VDC) group, with 24 employees dedicated to optimizing construction processes by creating a digital model of construction progress.

Hunter Cole, visual design coordinator, describes the group: "We are involved in almost all of the company's projects that require three-dimensional modeling."

Every regional office is equipped with DJI Inspire equipment. Whether it is aerial photography (photos or video) or creating detailed 3D models using photogrammetry, the drones allow us to collect information quickly, safely and inexpensively during all phases of construction.

Excavating the hospital construction site

During the construction of a hospital on a 61-acre (24.4 ha) site, VDC Group was approached by the local branch of a construction company. A subcontractor announced the completion of preparatory excavation work, but the branch manager was confident that the results of his work did not meet the planned documentation. So he requested the assistance of the VDC team to clarify the scope of work performed. Team coordinator Jesse Creech and field engineer Charles Curtis told us further.

"We were asked to find out the difference between the current site level and what was planned," Charles Curtis said.

Given the size of the site, drones were the best choice, since measuring the vertical profile by traditional methods is a very time-consuming and costly process.

Flying over the site

VDC Group hired Dronebase, a local drone service provider, to fly over the site with the help of a licensed pilot. "Dronebase flew the site using a Phantom 3 Pro and the DroneDeploy mobile app to plan and automate the flight. Given the size of the site, several sorties were required. The whole job took about an hour.

Since the map was to be used for comparative analysis, it was important that it match the existing drawings exactly when they were overlaid. Brasfield & Gorrie used ground control points (GCPs) to ensure accuracy (learn more about GCPs and map accuracy).

After flying over the site, Brasfield & Gorrie uploaded the images to the DroneDeploy cloud-based platform, which produced an orthomosaic map, a vertical profile map, and a 3D model the same day.

Comparing the plan to the actual state of the construction site

After receiving the map from DroneDeploy, Jesse then had to translate it into the same format as the plan drawings, aiming for maximum accuracy (i.e., that the geographic markings matched on both maps).

By inputting ground control points, he made sure the map was accurately aligned (possible with DroneDeploy's Premier plan). Next, Jesse exported the 3D model as a point set to third-party software. And from there, he converted the model to the desired coordinate system that was used to create the drawings (nowadays this can be done with DroneDeploy by just typing in the 4-digit EPSG code, but at the time the VDC team did it through third-party software).

A visual projection of how the vertical profile relates to the planned profile using a three-dimensional point set.

When the two models were properly aligned, Jesse was able to compare them. The result was a heat map showing the results of the earthworks and their deviations from the plan: areas marked in green matched the plan, blue were too low, and pink were too high.

Thermal map of vertical profile comparison: zones marked in green match the plan, in blue - too low, in pink - too high.

On Jesse's heat map, you can clearly see what the subcontractor did.

Based on the comparison, it was clear that additional amounts of soil needed to be taken out to achieve the required excavation rates.

Faster data collection leads to higher return rates

Using drones, VDC was able to evaluate excavation results much faster than with traditional methods without losing accuracy.

According to Charles, a field engineer, a job like this would have previously required more than 1,000 verification shots.

"Normally we would have used automated total stations to make a grid of elevation points. I would have had to use at least a 50 x 50 grid for a site like this. With a 61-acre site, more than 1,000 separate pictures would have been required with different settings. Combining this with regular work would have taken many weeks and would have seriously run out of schedule. That 1,000 shots would not learn about all the piles of waste soil or ditches, so we would have to explore all the contours of unintended details to maintain accuracy, which would greatly increase the number of shots," says Charles.

And even though 1,000 shots sounds like a lot, the drone easily captures much, much more data, allowing for a much more accurate model of the site's vertical profile.

"Getting multiple points representing an entire site in a couple of hours using a drone is proving to be a huge advantage for budget and schedule," Jesse said.

The speed of data analysis is basically comparable to other methods, but Charles is confident that the process will improve over time. "We've learned a lot through this process, and I feel that in the future we will be able to increase accuracy and significantly reduce the time it takes to process and analyze data," he said.

Overall, the example illustrated the tremendous savings in time and resources that Brasfield & Gorrie's drone surveying can provide. "The speed at which a drone can fly around and capture detailed images is very time-saving. The way I feel about it, we spent three times less time doing it than if we were doing it manually," Charles noted. Jesse summed it up this way:

"By spending a little time and money, we were able to figure out the outcome of the excavation and draw conclusions, which is otherwise a very expensive and time-consuming process. In this case, the ROI is very high."

Tips and best practices for using drones in the construction industry

Have you thought about incorporating drones into your construction business? Brasfield & Gorrie's VDC team can give you some tips:

Think through your task ahead of time. No two construction sites are the same, nor are the challenges with them the same. The worst thing you can do is report to the site without a definite flight plan;

set goals for yourself. Have an idea of what you will do with the information before you collect it, as this will allow you to choose the level of detail needed to accomplish the task;

Keep track of compliance with U.S. Federal Aviation Administration (FAA) requirements. Be prepared to refuse the customer if the execution of the order involves a safety or legal violation;

enlist the help of real pilots. "Brasfield & Gorrie employs a licensed pilot in order to be able to use drones for commercial purposes;

research the market carefully before purchasing drones - technology moves quickly.

https://stroyinfo.kz/eto-interesno/661-drony-na-strojke-kak-kontrolirovat-khod-raboty-s-primeneniem-bim.html

AUTHORS:

Professor Dubinin A.A. Candidate of Technical Sciences, IOC.

Graduate student of KazGASA Yerzhumanova U.S.