Rerouting access road underground keeps runway project on schedule

Feb. 29, 2016

When the Louisville International Airport needed to extend a runway, engineers were challenged to relocate a security access road that ran through the proposed extension site. With no space to move the road and utilities, engineers decided to reroute the road through a tunnel beneath the runway.

The challenge

In 2015, the Louisville International Airport wanted to install an Engineered Materials Arresting System (EMAS) as an added safety feature to help slow down jets if they are unable to stop on their own, protecting the passengers and limiting damage to the plane. To install the EMAS, they needed to extend a runway, but there was a security access road running right through the location where they needed to make the extension. There was no space to move the road or utilities.

The solution

Engineers from HNTB decided to build a tunnel so the security access road could be rerouted under the runway, making room for the expansion. To do this, four different retaining walls to support the roadway leading up to the tunnel were needed.

The specifying engineer, HTNB, specified a pile and lagging wall, or an option for small segmental blocks. Mike Mattingly, PE, from Mattingly Engineers, said Redi-Rock was the final choice because the price was significantly less, installation was faster and the system gave them the versatility they needed.

Redi-Rock is a precast, large block retaining wall system that stacks together like giant Lego blocks using a knob and groove design. Redi-Rock offers a variety of products, including gravity and reinforced blocks that can be used together, allowing designers to build walls in the safest, most efficient ways possible.

Engineers had several issues to consider when designing the walls for this project. According to Mattingly, sloping bedrock, utility duct banks, a utility manhole, and a tight construction schedule were all challenges they had to work through as the project progressed.

"Installation was a very time critical situation...I originally gave them a time frame of 35 working days to get this job up and completed; we got it done in 23 days," said Irvin Vittitow, co-owner of Redi-Rock of Kentuckiana, producer and installer of the Redi-Rock blocks on this project.

One reason Redi-Rock of Kentuckiana finished the installation so quickly was because they used a Towtem grapple that can pick up the blocks and put them in place in less than 30 seconds per block. This eliminated the need for a man on the ground or on the wall to hook and unhook blocks, saving them money in the end. The base course is set with a traditional chain and excavator hook up so they could ensure that the bottom course is perfectly level, said Vittitow.

The outcome

The project included four gravity and Positive Connection (PC) walls, all in the Limestone texture. In total, there was 20,943 sq ft of wall face, and 385 Redi-Rock caps were used, giving the walls a finished look. According to Mattingly, all of the walls were designed in accordance to AASHTO LRFD 2012.

"In the end, to accommodate all of the various site and project constraints, six different typical sections were developed and used. These included a gravity a soil retained zone; a gravity system using 28-in. blocks and cast-in-place concrete backfill; a gravity system in front of a (sheet piling to protect the manhole) per AASHTO; a reinforced system with a soil-retained zone; a reinforced system with a soil and rock retained zone; and a reinforced system with a rock retained zone and a (sheet pile)," said Mattingly.

"This project showed that with a little creativity, the options for solving complex situations are unlimited," Mattingly concluded.

Find out how Redi-Rock can help on your next roadway project at

Redi-Rock International

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