Measure twice, cut once: Using drone data to calculate concrete volume

Earlier this year, EMJ completed an expansion at Ruby Falls, a tourist attraction in Lookout Mountain, Tenn., that boasts the nation’s largest public underground waterfall. Our team constructed a new lobby, retail space, pedestrian mall, and more next to the original, historic castle that sits more than 1,000 feet above the underground waterfall.

The expansion required removal of a significant amount of rock to create a pad for the new construction. Considering the site’s location on a mountainside above an underground cavern, the team carefully drilled out the rock section by section, rather than blasting. As documented in a recent Ground Up podcast, the rock removal process required precision planning, logistics, and execution by all project team members. It also required careful consideration for how to prepare the resulting site to endure the elements for many years to come.

Among those considerations was waterproofing and the best method to ensure the exposed rock could withstand the elements. Of particular concern was a void between the new building and the rock wall. This gap was created when the team carved out the rock to create the building pad. The design team presented two options for EMJ to consider: apply a vinyl-waterproofing product or fill the space between the building and the mountain with concrete.

But, here was the catch. While the team could estimate the cost of the vinyl waterproofing, it was impossible to measure the gap and estimate the cost of the concrete.

The team called on Caleb Wickersham, EMJ Virtual Construction Engineer and licensed drone pilot, who had already flown the site and created a 3D model of the mountainside using photogrammetry.

Caleb layered the architect’s building model next to his mountainside model. Using his previous calculations, he was able to determine the volume of the space between the building and the mountain, which provided the amount of concrete needed to solve the waterproofing issue.  From this, the team calculated the concrete cost, and in comparing it with the vinyl-waterproofing cost, the vinyl product was the more cost-effective and prudent option for Ruby Falls.

There is an old adage that applies to construction, “Measure twice and cut once.”  In a figurative sense that means to plan and prepare in a careful, thorough manner before taking action. Using construction technology, that is exactly what the Ruby Falls team did, helping make sure its recommendation to the client was accurate.

Check out this video of Caleb’s handywork.

Related story:

EMJ’s Chattanooga team wraps up Ruby Falls expansion

 

Photogrammetry offers easy, accurate solutions for owners and trade partners


A site capture of Firestone in Opelika, Ala., offers measurements at 1-inch accuracy through use of survey control points.

 

Construction of the Firestone store in Opelika, Ala., required a series of cut and fills before construction began. Wanting to ensure that the site’s grade was maintained and that stormwater drainage requirements were achieved, the EMJ Special Projects team enlisted the help of Caleb Wickersham, Virtual Construction Engineer and licensed drone operator.

Using GPS coordinates and other data, Caleb conducted programmed, automated flights along the same path at each stage of the site’s preparation. During the flights, the drone captured high-resolution images of the site from which Caleb applied photogrammetry.

“Photogrammetry offers construction teams the ability to capture measurements and record the site how it was at the time of flight,” said Caleb.

The measurements obtained through this process are within an inch of accuracy and offer endless applications in the construction industry.

“It allows us to go back if something goes wrong and see where and when the problem occurred or can be used to hold project participants accountable for their contracted responsibilities,” said Caleb. “Taking measurements can also offer data that would otherwise take extra time, effort and money to obtain. For example, after a drone flight at the Hampton Inn site in Decatur, Ga., we captured the height of surrounding buildings. This was then used to discuss crane logistics and security camera locations for the site.”

At EMJ Construction’s Ruby Falls project in Chattanooga, Tenn., the team requested Caleb’s help in determining the amount and estimated cost of concrete.

“It allowed the project team to see how much concrete would be needed to fill the space between a wall and cliff face and make decisions based upon that volume estimate,” said Caleb.


This photogrammetric 3D model was used for confirming measurements at Ruby Falls. Green photo projections represent where the photos were taken in 3D space.

 

Drone flights cost roughly $500 per flight, but the cost can vary based on the number of flights and the job site location. Teams receive their drone deliverable package typically within 48 hours of the drone flight, and Caleb and his team can provide them anything from an orthomosaic sitemap (a top down view of site at high resolution) and volumetric calculations to 360 photos and video.

“Additionally, EMJ clients are able to see the data as we capture it,” said Caleb. “This allows them to see a timeline of the building as it rises from the ground and assists in communicating progress. Subcontractors also benefit from the data and the availability of an active, up-to-date map of the site as they develop their execution plans.”

For more information on photogrammetry or to enlist the Construction Technology team’s help with a project, contact ConstructionTechnology@emjcorp.com.

Caleb Wickersham joined EMJ Corporation in 2017 and is focusing on building EMJ’s field technology capabilities, such as drones, Matterport and laser scanning, as well as assisting with BIM coordination and other related tasks.