Keller has announced that it has successfully completed work on what is believed to be the largest permanent soil nail wall ever constructed in the US at over 1.2km long and covering more than 23,000m².
Completion of the wall clears the way for the construction of a new stadium for Major League Baseball’s Texas Rangers – the Globe Life Field – which is set to be completed for the 2020 season.
The work follows on from Keller subsidiary Hayward Baker’s delivery of a similar wall 12 years ago at the Dallas Cowboys’ AT&T Station 12 years ago.
“There have been a lot of improvements in equipment and processes since we worked on the Cowboys’ stadium, and these combined with our previous experiences and good relationship with main contractor for both schemes, Manhattan, meant we were able to successfully win the contract,” said Hayward Baker division manager Marty Schrantz.
According to Keller, the Dallas project was relatively straightforward compared to the Texas Rangers’ scheme.
Ground conditions comprised clays, sandstone and shales, contained many fractures, joints and weak planes that had to be accounted for. Also, randomly scattered throughout the site were dense, irregularly shaped boulders of hard, limy sandstone, which required partial removal. This had to be done with special care so as not to cause cavities, which would have been problematic for the shotcrete facing.
The retaining wall also had to follow a line with numerous juts and corners. “For the latter, we introduced an alternate hybrid anchored drill shaft system,” said Hayward Baker senior engineer Joel Clark.
“This was initially developed on the AT&T project and alleviated the soil nail congestion and crossover at either side of the corners, while providing the resisting forces needed to retain the inherently unstable wedges of ground at these points.”
An anchor drilled system was also required in some places due to utility services for an adjacent entertainment complex under construction. Fellow Keller company McKinney Drilling was brought in for the drilled shafts.
“The schedule was very tight and this was a large project, requiring multiple rigs and a lot of coordination with other trades,” said Keller district manager Austin Pruitt. “We had to be flexible to meet the changing daily demands and the boulders were challenging. If we hit one, we’d put a core barrel on and drill through it if we could. If not we’d dig it up. We also had to use temporary casing because of the sandy soils. It was hard work but it all went well thanks to brilliant coordination and a great team effort all round.”
According to Keller, advances in monitoring also benefitted the project. In a statement, Keller said: “Historically, a wall of this size would require extensive resources and ongoing efforts to monitor deflection at critical sections during construction. However, fellow Keller company Geo-Instruments was able to provide a comprehensive and technologically advanced monitoring program that saved time, increased accuracy and minimised field effort.”
This included three automated motorised total stations and four automated vertical inclinometers to provide continuous, real-time monitoring.
“Once installed, they generated data without any additional field work,” said Keller. “The monitoring, with alarms set at predetermined thresholds, provided assurance that actual deflections remained in line with those predicted in the design.”