Project DetailsLocation: Charlotte, North Carolina
Owner: Charlotte Area Transit System (CATS)
Contractor: Archer Western Contractors; Balfour Beatty Infrastructure, Inc.; Bonn-J Contracting, Inc.
Engineer: Parsons; STV/Ralph Whitehead Associates, Inc.
The Lynx Blue Line opened in 2007, as the first major rapid commuter rail service in North Carolina. RECo provided twenty Reinforced Earth® MSE structures for the construction of the initial line, which starts near I-485 south of Charlotte, and ends at 7th street downtown. Almost 275,000 square feet of MSE wall was used on the project, as well as nearly three miles of precast coping. In 2018, the Lynx Blue Line Extension opened, which continued from 7th street all the way to the UNC-Charlotte campus. RECo provided another 290,000 square feet of MSE wall for Segment A of the job.
The retaining walls are used to support the electrified rail line, roadways, and even pedestrians as they walk to the platforms.
Several special design aspects were implemented in the design of the MSE walls:
- Some sections of the MSE walls are designed as back-to-back structures, meaning they are double-sided ramps with soil reinforcements overlapping in the center of the MSE wall volume. This type of design allows for a reduced lateral earth pressure to be assumed in design of both sides of the ramp, increasing the economy of the wall materials.
- Accommodation of structure foundations and conduit within the MSE volume for the rail system.
- A bridge abutment on a tight skew required an acute corner, in which the nose of the abutment incorporates a binwall design in addition to the typical MSE considerations.
- The use of cast-in-place concrete as a replacement for bottom level precast panels in select locations, in order to allow large concrete drainage pipes to penetrate the face of the walls. The cast-in-place concrete incorporated soil reinforcement connections similar to precast wall facing panels.
- Slip joints were spaced at regular intervals on the facing of some walls to increase the allowable differential settlement.
- In areas that required a handrail along the top of the wall, precast coping was anchored to the top MSE wall panels.
- A unique architectural finish is incorporated into the concrete structures throughout the rail system.
The Lynx Blue Line has 26 stations and runs northeast/southwest for over 20 miles through the city.
Overall, the Lynx Blue Line has 26 stations and runs northeast/southwest for over 20 miles through the city. Charlotte’s light rail system also includes the CityLynx Gold Line, which is a free-to-ride streetcar. It opened in 2015, and has extensions planned for completion in 2023.