April 21, 2003 -- With more than $2 billion in current development, the Milwaukee, Wis., skyline is changing.
But at the same time, beneath the surface and invisible, the Milwaukee Metropolitan Sewerage District (MMSD) is in the midst of a multi-year program to renovate the downtown interceptor sewers that range in age from 80 to 120 years. "Because it's all downtown, cut-and-cover construction is out of the question so we are using trenchless technology methods for the rehabilitation" said Bob Plecash MMSD project manager.
The district recently installed 63-inch diameter HOBAS centrifugally-cast, fiberglass-reinforced, polymer mortar (CCFRPM) pipe on the Clybourn Street section of the Central Metropolitan Interceptor Sewer (MIS) Rehabilitation Project with the goal of adding 50 years to its service life. The existing 72-inch monolithic concrete interceptor was sliplined with the CCFRPM pipe.
A preliminary evaluation of the interceptor concluded that two-thirds of the 80-year-old pipeline needed structural rehabilitation and the other sections showed deterioration to the point that future corrosion had to be halted. The engineering firm of Alvord, Burdick & Howson (AB&H) was hired to evaluate the rehabilitation options. "We knew that hydrogen sulfide was present," said Bill Meinholz of AB&H. The firm evaluated the material options including several liners for the structural sections and various coatings for the non-structural sections of the line, but they were not convinced that all of the options would stand the test of time.
"HOBAS could prove that fiberglass could be a stand-alone structural material," stated Meinholz, who was not as confident in some of the other material choices. Besides the structural and corrosion considerations, AB&H also needed to insure that the flow in the rehabilitated line was adequate. Minimum IDs of the pipe to be rehabilitated limited the material choices even further and excluded most profile wall products like PVC and HDPE. According to Meinholz, "The material choice was based on a 50-year economic evaluation. Consistent with this life cycle cost analysis, CCFRPM could provide structural reliability, corrosion resistance and maintain the flow long term."
CCFRPM pipe, cured in place pipe (CIPP) liner and fiberglass-reinforced plastic (FRP) liner were the materials the specifications allowed in the structural sections. All of the contractors that bid the project chose sliplining with CCFRPM for the straight sections. The low bidder, Super Excavators, Inc., of Menomonee Falls, Wis., ultimately chose it for the entire project.
The contractor ordered a combination of low profile bell and flush joints to slipline the existing deteriorated 72-inch diameter monolithic concrete sewer. The stiffness classes of the pipes supplied to the project ranged from 36 to over 60 stiffness for the deep, 70-foot depths. Another reason Super Excavators chose CCFRPM pipe was their confidence that installation would be easy, based on their prior experience with the pipe.
The contractor installed the pipe with an in-house designed pushing mechanism that utilized two hydraulic rams and a plate, which backed to the existing sewer. The maximum push distance was 3,600 feet. "And we could have pushed more," said project superintendent Gregg Rehak. The long push was made necessary by the presence of utilities that could not be easily relocated which limited shaft locations. Two separate 100-ton jacks were installed to make the push. The HOBAS pipes were light enough and smooth enough that pushing by this method was simple, requiring only 24 tons of force (well below their more than 200 ton capacity). Several other smaller segments were sliplined with drives averaging over 1,000 feet.
Among the greatest benefits of using CCFRPM were the short sections, which were made to order to custom, fit this particular installation. Six separate radius curves totaling approximately 1,300 feet were relined with shorts that fit the existing radius of the sewer. Super Excavators supplied actual ID measurements and lengths of the deteriorated sewer to HOBAS engineers who then designed a layout scheme. "I can't believe how well it went. We did all the measuring and HOBAS took it from there." was the response from Rehak.
HOBAS also manufactured short pipes for straight sections that were contained between curves and otherwise inaccessible. These shorts were pulled through the curves and then installed with a winch. Even in this difficult installation area, Super Excavators was able to keep production rates up to 22 to 25 pipes per day.
The project progressed very smoothly and grouting was uneventful. The new pipes were filled about half-full with water and a lightweight foam grout was used to fill the annular space. The runs that were grouted averaged about 500 feet.
MMSD officials are satisfied because they are confident that sliplining with CCFRPM pipes ensures that the structural integrity of the line will be maintained for many years to come. AB&H plans to include the pipe on future projects as well.
Meinholtz said that Super Excavators is not only delighted with the product but with the quality of service they have received from HOBAS throughout the project.
HOBAS pipe is manufactured in sizes from 18 inches to 102 inches in pressure and non-pressure classes. For more information, please contact HOBAS at 800-856-7473, 281-821-2200 or e-mail at [email protected]. Facts are also available at www.hobaspipeusa.com.
