Large Pipe Jacked Half Mile In One Drive

September 2010 Vol. 65 No. 9
The pipes are being supplied by Hobas, and are the largest CCFRPM pipes made to date with an OD of 118 inches.

Low loads, quick installation
The smooth and even outer surface of the centrifugally cast fiberglass pipes helped the contractor breeze through one of the project’s challenges. Original plans called for a 2,800-foot section to be jacked from both ends and meet in the middle. However, when using CCFRPM pipes, the construction plan could be modified so that the section was jacked precisely with one single drive and from one side only.

Despite the anticipated low friction forces, the contractor followed the project plan and erected an intermediate jacking station (IJS) every 328 feet. These were insurance, but in practice, only one of these (the last) was put into service. This was the longest drive of the project and was conducted in two shifts working 24 hours per day and seven days a week. After its completion, the intermediate stations were replaced by CCFRPM manholes and the IJS were reused for different sections of the project.

The tunneling progressed at an average of nine feet per hour with the separator processing 76 tons of soil per hour. The cycle time between pipes (disassembly and reassembly of electric cables, slurry pipes and hydraulic hoses) took about 40 to 60 minutes. At this rate, an average of 10 pipes could be installed per day. Due to the rapid production, it was possible to complete the first section of pipe installation weeks ahead of schedule. The contractors’ expectations were certainly exceeded and allowed them to commence work on new sections.

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Jacking challenges, including the close proximity to a subway, were overcome with advance planning and precise remote controlled jacking.

Trenchless option
A trenchless method was chosen due to the river crossing but, also because the pipeline route runs beneath a six-lane road. It is in this section that a single drive of nearly 3,000 feet broke the record of longest single drive for the project. Several impressive jacking runs were accomplished on this project, setting a global record for the longest fiberglass pipe jacking installation for 3000 mm.

Jacking challenges, including the close proximity to a subway, were overcome with advance planning and precise remote controlled jacking. At one location the clearance between the jacked pipeline and the subway was only two feet.