Mosley Builds Tunnel Under St. Louis Runway

Wed July 09, 2003 - Midwest Edition

Neither rain, nor sleet, nor snow, nor sub-freezing temperatures stopped Mosley Construction from laying the concrete foundation for Missouri’s first traffic tunnel – Lindbergh Boulevard Tunnel at Lambert-St. Louis International Airport.

St. Louis-based Mosley recently completed placement of more than 16,000 cu. yds. (12,232 cu m) of concrete comprising the foundation and footings for the new tunnel. The project originally was scheduled to start in July 2002, but delays in site work pushed the start of the tunnel work back to December, creating challenges for the construction team.

“We had to overcome many obstacles related to performing concrete work in winter conditions,” said John Wilkerson, Mosley’s project superintendent. “The substrates had to be thawed before we could place the concrete, and we then had to maintain warmth as the concrete cured, incurring several delays. This 16,000 cubic yards of concrete serves as the foundation for the entire tunnel, so it was vital we take the time to ensure it was done right.”

The tunnel will be the first traffic tunnel in the state of Missouri and will be among several airport-related tunnels in North America, including those in Detroit, Cincinnati and Toronto.

Mosley began pouring a 6-in. (15.2 cm) mud slab immediately after excavation was completed. After reinforcing steel was installed, Mosley poured the footings and installed all necessary formwork, waterstops, blockouts, keyways and bulkheads. Mosley also placed concrete along the entire length of the tunnel for the drainage encasement. The mud slab and footings for an ancillary building at the southeast end of the tunnel also were included in the scope of Mosley’s work.

“It had to be the worst winter — precipitation wise —that I have ever seen in the St. Louis area,” said Wilkerson. “First, we had rain, then more rain, then snow and then frozen conditions. We were pouring 20-ft. wide footings, with a lot of steel in them. Rain or snow, it still got wet and it had to thaw out and dry out. We had to melt that stuff out before we could continue work.”

They used concrete blankets — tarpaulin with fiberglass insulation — to keep the rebar warm enough for the concrete. Propane heaters under the blankets kept the temperature up, said Wilkerson.

Wilkerson said that concrete pumps were used whenever and wherever possible to keep the concrete flowing and pouring efficiently at three times the rate of concrete trucks.

“Access for the pump was a problem. The weather conditions also made it difficult to even get concrete trucks into the site. They got stuck down to their axles in mud. We ended up pulling them along with highlifts and bulldozers,” said Wilkerson.

“We worked straight through from December to May because the whole airport renovation project needed to be kept on schedule. The tunnel is an important part, but just one part. We ended up making up lost time. The concrete pumps helped make up a lot of time. They have a higher rate of productivity than pouring out of a truck – 200 cubic yards an hour versus 60 to 80 cubic yards,” Wilkerson said.

The cold weather made things difficult for the crew, as well.

“Production is a lot slower when you have to wear rubber boots and a lot of bulky clothes,” explained Wilkerson. “The project was only supposed to last four and a half months in warm weather. Despite the cold weather, we completed the concrete in five months. We used more people to get on schedule and keep on schedule. Larger crews worked long days with many many over time days.”

He said that vinyl water stop was inserted in the concrete the entire length of the two exterior walls to make sure that water from the outside did not come in. This also helped ensure that when they backfill it later with rock and dirt any settling rain will stay outside the tunnel.

He said that every time before they made a pour, they had to heat up the rebar or double check the temperature of the steel to be sure it was in compliance with acceptable safety standards. On any given day, five carpenters, eight laborers and a project engineer were at the site.

“Conditions were constantly changing. The engineer was constantly making new calculations. We had to justify the quantities of concrete we were using. If the sub-strata was not acceptable, we would have had to remove the wet material. Instead, footings were dug deeper,” Wilkerson explained.

All told, more than 16,000 cu. ft. (453 cu m) of concrete was poured — 20 ft. (6.1 m) wide and 3 ft. (.9 m) deep, stretching for .25-mi. (.4 km).

The high-tech quarter-mile tunnel, when completed, will carry busy traffic beneath equally busy air traffic on the runway above.

The tunnel will accommodate two lanes of vehicles traveling in each direction with space to add an additional lane in each direction in the future. When completed next year, the $49-million tunnel will route up to 65,000 cars a day under a new runway.

Water within the tunnel will drain from the south to the north end, where it will be piped through a large storm water drain to a detention basin approximately 1 mi. (1.6 km) away from the tunnel.

The tunnel is designed so a 1.25-million-lb. (566,990 kg) aircraft can land directly on top of it without damage. The concrete roof will be 5 ft. (1.5 m) thick and the walls will be 3 ft. thick.

When completed, the tunnel will include approximately 50,000 cu. yds. (38,227 cu m) of concrete. Twenty-five-foot (7.6 m) exterior walls and a wall separating northbound and southbound traffic will be 3 ft. thick, topped by 5 ft. of concrete. Four to 10 ft. (1.2 to 3 m) of rock and dirt will then separate the tunnel from the runway.

Initially, each direction will include two 12-ft. (3.6 m) lanes, a 12-ft. (3.6 m) shoulder on the right, a 10-ft. (3 m) shoulder on the left and pedestrian connecting doors spaced every 300 ft. (91 m).

McCarthy Mosley II, A Joint Venture, composed of McCarthy Building Companies and Mosley, is managing the tunnel project. Mosley self-performed the initial concrete work.

Mosley’s project team for the foundation and footings included Wilkerson and Russ Dodson, project engineer. Scott Beckett of McCarthy is the project manager for the McCarthy/Mosley joint venture.