Tuesday, May 21, 2024

NEW YEAR’S HOLE-OUT IN TEXAS

It was a great start to the New Year in 2023 for the Melcar Group as its Akkerman SL82P MTBM holed-out on the Sims Bayou tunnel project in Houston.

It was a great start to the New Year in 2023 for the Melcar Group as its Akkerman SL82P MTBM holed-out on the Sims Bayou tunnel project in Houston, Texas, USA. The US$18.9 million project was designed to increase the overall capacity of the region’s drinking water by making the critical connection of the large diameter water pipeline from one of the City’s treatment plants.

Since the 524 ft (159.7 m) microtunnel was the last segment of infrastructure to be installed, project representatives as well as the 285,000 plus residents of the Sims Bayou watershed are pleased to see the project completed.

Awarded in the autumn of 2017, the estimated construction schedule for the entire scope of the project was originally 655 calendar days (21 months) to complete, however shaft construction proved to be extremely difficult along Houston’s Sims Bayou which caused delays. A combination of flowing ground and high hydrostatic forces created safety issues during the initial shaft construction which require project teams to mitigate prior to tunnelling.

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The Melcar Group mobilised its Akkerman SL82P slurry microtunnelling system to the Sims Bayou project jobsite in the autumn of 2022 while the launch shaft construction was being safely completed. The SL82P MTBM included a mixed face cutterhead designed for the varying soil strata with running sand and significant ground water. To battle the extreme hydrostatic loads that hindered shaft construction, Akkerman supplied a launch portal and pipe brake that integrated with the MTBM jacking system to maintain face balance and eliminate any push-back that may occur. The periphery-drive MTBM was powered by a 400 hp onboard electric power pack and could produce over 350,000 ftlb (474,500 Nm) of torque while being remotely controlled and monitored from above ground.

Melcar launched the Akkerman SL82P on 9 December and it arrived at the reception shaft on line and grade after 23 days of operation. Although the installation time for a 20 ft (6 m) section of 80 in (2,032 mm) diameter steel casing averaged just over two hours during the microtunnelling process, setting additional sections of pipe in the launch shaft often required the remainder of the shift. Since microtunnelling was originally scheduled to begin in 2020, the stored pipe developed inconsistencies that required attention before it could be put together. This limited the crew to an average of around 20 ft (6 m) per shift with a few days installing 40 ft (12 m) per shift. Other factors contributing to production levels including very limited site space with only 4,700 ft2 (437 m2). of laydown and setup area, pipe staging 0.90 miles (1.5 km) away, deep shaft depths and working in a densely populated residential  neighbourhood. Overall thrust loads gradually increased along the alignment and a sealed intermediate jacking station was installed, however not used. With the assistance of an Akkerman MTBM technician that was onsite for the duration of the tunnelling, daily operations were monitored including the break-out thrust which peaked at 625 t and quickly dropped to a dynamic thrust load of 320 t after movement and additional lubrication was applied.

The City of Houston has a history of using innovative approaches while enhancing their public works infrastructure. As early as the 1940’s, the US Army Corps of Engineers (USCOE) and the local flood control district worked with the local community to strategise a plan to widen the Sims Bayou for flood and erosion control while maintaining natural ecosystem to encourage habitat diversity. The reconstruction of the Sims Bayou was the first of its kind to incorporate this type of floodway construction and has influenced other professionals to seek similar innovative solutions. Today, the City of Houston is using innovative trenchless technologies such as the Akkerman slurry microtunnelling systems to tunnel underneath the Sims Bayou to provide clean water for their residents while minimising the social and environmental impacts other construction methods can impose. As North America’s only manufacturer of slurry microtunnelling equipment, Akkerman, Inc. is proud to have been a part of this team and look forward to the continued advancement of the industry.

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