September 2010 Vol. 65 No. 9
Features
Large Pipe Jacked Half Mile In One Drive
Europe, like the United States, is struggling to upgrade its infrastructure. In Poland, for example, over 1,000 wastewater treatment plants need to be constructed or upgraded in order to meet European standards which take effect in 2015. Warsaw, the capital and largest city in Poland, has many planned upgrades, including a recent two-year-long project which will provide added capacity and decrease overflows.
One of the driving forces for this new project was environmental, as it is estimated that 30 percent of effluents have been flowing directly into one of the longest and most important rivers in Poland. Warsaw’s proximity to the Vistula River, the environmentally fragile Baltic Sea and the nearby Carpathian Mountains, home to the largest European population of brown bears, made the project a priority. The environmental aspects coupled with the growing population of the area meant the project should proceed quickly.
The Czajka waste water treatment plant is currently being constructed on the river bank of the Vistula River in Warsaw. After its completion, it will treat 80 percent of the Polish capital’s effluents and make sure that no more untreated sewage will harm the flora and fauna along the Vistula.
As part of the development plan, a collector leading to the plant is also under construction. Due to this project’s size, it was divided into three phases. The first phase is a 3.5 mile jacking project along the right side of the Vistula, the second a 4,600-foot jack along the left bank. These pipelines will meet in the third section, the river crossing.
The pipes for all three phases are being supplied by Hobas, and are the largest centrifugally cast fiberglass reinforced polymer mortar (CCFRPM) pipes made to date. Phases one and three utilize 118-inch OD pipes. The river crossing consists of two parallel, 63-inch diameter lines installed within a 15-foot diameter concrete tunnel.
The consortium of contractors, Hydrobudowa 9, PRG Metro and KWG (all belonging to the PBG Group) have now completed the first pipeline section which includes nearly a mile of jacking utilizing two Herrenknecht microtunneling machines. Proximity to the river means the groundwater is high; the typical water table is just below the surface.
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.
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.
CCFRPM was not the least expensive piping material for the project but the higher material cost was outweighed by the savings. For example, a 30 percent reduction in soil extraction was possible due to the high-strength thin walled product, which creates a smaller OD for the same ID. Construction equipment could be kept small and to a minimum, which was crucial in this tight space. Fast onsite assembly, long life expectancy and low maintenance all factored into the cost analysis.
CCFRPM pipes have experienced success globally in long jacking runs.
FOR MORE INFORMATION:
Hobas Pipe USA, (800) 856-7473, (281) 821-2200, www.hobaspipe.com
Herrenknecht USA Inc., (253) 804-6511, www.herrenknecht.com
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