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Aggressive Phasing and Strategic Detours Help Dallas Area’s $370M I-635/SH 121 Interchange Project Finish Six Months Early

by: Julie Devine
Concrete is poured on one of the many bridges that are part of the I-635/SH 121 Interchange project near Dallas Fort Worth International Airport.
Concrete is poured on one of the many bridges that are part of the I-635/SH 121 Interchange project near Dallas Fort Worth International Airport.
A lack of funding delayed the $370 million Interstate 635/State Highway 121 Interchange project north of the Dallas Fort Worth International Airport (DFW) a decade ago – but once funding became available, the project finished six months ahead of its scheduled completion date.

Design-Build Contractor NorthGate Constructors – a joint venture between Fort Worth-based Kiewit Texas Construction L.P. and San Antonio-based Zachry Construction Corporation – rebuilt and widened 3 miles of SH 121 in Grapevine, Texas, to accommodate a new interchange at I-635 and new direct connectors for FM 2499 and SH 26.

In addition to reconstructing existing roadway, the project added a lane on both northbound and southbound SH 121, widened six existing bridges, and built 16 new bridges. The new interchange at I-635 features a collector distributor lane in each direction of SH 121, which allows traffic to merge, exit, and enter the highway without disrupting traffic flow on the mainlanes. The project also widened the existing direct connectors and frontage roads and increased capacity along Bass Pro Drive.

Designed to relieve traffic congestion, reduce travel times, and increase safety, the project is a partnership between the Texas Department of Transportation (TxDOT), Tarrant County, the City of Grapevine, the North Central Texas Council of Governments, and NorthGate Constructors.

How It Happened
Initially, the I-635/SH 121 Interchange project was included in the DFW Connector project, an 8.4-mile, $1.02 billion effort that rebuilt portions of four highways, two major interchanges, and five intersection bridges.

At the time, TxDOT selected NorthGate Constructors as the best-value proposer to deliver the design-build DFW Connector project as part of a Comprehensive Development Agreement finalized in October 2009. Construction of that project began in February 2010 and the main portion reached substantial completion in November 2013. Final project acceptance occurred in March 2014.

However, at that point, funds weren’t available to deliver the entire scope and the I-635/SH 121 interchange had to wait. In 2017, TxDOT secured funding through the Texas Clear Lanes initiative, which aims to reduce congestion in metropolitan areas. They then negotiated a plan to rebuild this portion of the original project.

“The contract for the I-635/SH 121 Interchange project was the result of a change order negotiated between TxDOT and NorthGate Constructors based on pricing of the original contract,” said Mike Schram, Project Director for NorthGate Constructors.

Design for the I-635/SH 121 Interchange project began in February 2018 and construction commenced in July 2018. On August 2, 2021, TxDOT and NorthGate Constructors hosted a virtual ribbon cutting ceremony, six months earlier than originally planned.

“The construction team and TxDOT came up with a great plan for the phasing of the job that allowed the team to progress the schedule,” Schram said. First, “The project team set an aggressive goal of completing utility relocations and structures work as early as possible in the phasing of the job to allow for the grading and paving work to open up sooner.”

In addition, “After the design was complete, we added two different detours that allowed the construction team to progress the schedule of two different bridges,” Schram said. “Those detours tremendously helped to achieve the early delivery of the project.”

Over Railroads and Creeks
With the aggressive schedule, the project’s bridge work presented a variety of challenges.
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For example, “All eight bridges that were demolished had a road or creek under them,” Schram said. “This required the team to have full weekend closures to do the work. The amount of engineering and planning that goes into a 48-hour demolition operation is staggering. However, the team’s planning efforts showed when the bridge demolitions were performed without any hiccups and most of the highway openings occurred six to 12 hours earlier than expected.”

In the construction work, five of the new bridges crossed over Cottonwood Creek and 3 of the bridge widenings occurred over the Cotton Belt Railroad line.

“All of those operations required extra precautions,” Schram said.

As a further complication, two of the bridges widened on the project required rehabilitation, including replacement of the backwalls on the abutments. Crews added expansion joints at both abutments and at the middle bent of the bridge. The girder bearing pads were also replaced at the locations where the expansion joints were added. To replace the bearing pad, a hydraulic ram lifted each girder at that abutment or bent at the same time. The most that was lifted at one time was 22 girders.

In addition to those lifts, “We built a lot of abutments in the air to allow for the bridges to progress at the same time the wall was being built,” Schram said.

Keeping the Project Moving
The project’s proximity to DFW Airport required a permit from the Federal Aviation Administration to operate cranes on the construction site, but the location caused no further complications.
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To maximize efficiency, NorthGate Constructors used an onsite batch plant for mixing concrete. An onsite crusher took waste concrete from removals and demolished bridges and created the roadway base for the subgrade under the concrete paving.

Crews reconstructed all the roadways on the project, using 13-inch concrete paving on the mainlanes and 10-inch concrete paving on service roads. The finished project now provides faster, safer travel and increased connectivity between I-635, SH 121, SH 26, and FM 2499.

Key Project Personnel
Owner – Texas Department of Transportation; Prapti Sharma, Deputy Project Manager
Design-Build Contractor – NorthGate Constructors, a joint venture of Kiewit Texas Construction L.P., Fort Worth, Texas, and Zachry Construction Corporation, San Antonio, Texas; Mike Schram, Project Director; Ross Schroeder, Quality Manager; Tom Grim, Project Sponsor
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