HOBAS Pipe 'out of sight, out of mind' in Seattle area
Prior to 2005, that might have been true of the 348 miles of interceptor sewer lines that run beneath streets in the King County service area. In an effort to improve the system, the 40-year-old regional utility was to complete several sewer construction projects this year. One of these is the Lakeland Hills Force Main, a 24-42" diameter gravity sewer line at the end of a main pump station. Over 8,000 linear feet of HOBAS CCFRPM pipes were chosen for this project...
• Project involves both tunneling and open cut installation -- part of it runs under a railroad.
SEATTLE, WA, Feb. 20, 2006 -- Mount Rainer, the Space Needle and HOBAS pipe.
What do they have in common? They're all in King County, Wash.
Located on the Puget Sound, King County is home to many things. This includes an extensive Wastewater Treatment Division that serves 18 cities, 16 local sewer agencies and more than 1.4 million residents.
The usual description of many sewers is "out of sight and out of mind." Prior to 2005, that might have also been true of the 348 miles of interceptor sewer lines that run beneath streets in the King County service area. In an effort to improve the system, this year the 40-year-old regional utility will complete several sewer construction projects. One of these is the Lakeland Hills Force Main, a 24- to 42-inch diameter gravity sewer line that begins at the end of one of their force main pump stations. Over 8,000 linear feet of HOBAS centrifugally cast, fiberglass reinforced, polymer mortar (CCFRPM) pipes were chosen for this project.
One of the greatest concerns during the design phase was the corrosion resistance of the piping material because gases released by the sewage could attack many traditional materials. "Since this project starts at a terminus of one of our force mains, we needed a pipe material that was resistant to corrosion from acid attack," said John Abdalkhani, PE, project engineer with King County's Wastewater Treatment Division.
HOBAS CCFRPM pipes are stringently tested in accordance with ASTM D3681, and meet the requirements of ASTM D3262 for sanitary sewer pipes. The test is performed in a 1 normal H2SO4 environment (pH near 0.5) to mimic a very septic sanitary sewer. The projected design life in this environment has been calculated at more than 100 years.
Other considerations included the pipe's ability to resist the dynamic live loads and static overburden. The soils were varied and poor in some areas with anywhere from four to 50 blows per foot. Luckily, they were generally good and consistent at embedment cover depths of nine to 17 feet.
To meet the structural requirements, HOBAS supplied pipes with a minimum of 46 psi pipe stiffness and, where required by site conditions, a stiffness of 72 psi. HOBAS pipes are structurally proven to safely handle E-80 rail and HS-20 roadway loading.
"Our project also involved the installation of the gravity sewer main under existing railroad tracks, one through tunneling and a few via open cut. We needed a pipe that had the right structural characteristics," explained Abdalkhani. Approved crossings included tracks owned by Union Pacific, GSA and The Boeing Company.
The overall engineering design, which included hydraulic analysis, plan and specification development and other civil work, was done in-house by King County. CH2M Hill consulting engineers of Bellevue, Wash., provided support and expertise in a variety of areas including geotechnical engineering, traffic engineering and pipe tunneling.
Although the King County Wastewater Treatment Division had used HOBAS pipe before, this is the first time Abdalkhani had used it on one of his projects. He explained, "Some of the engineering support on this project was done by CH2M Hill consulting engineers. They are the ones who recommended using HOBAS pipe." Due to the design conditions, no other pipe materials were allowed on the gravity portion.
With 200 days to substantial completion, the job was fast paced. "The assembly on site went faster than any pipe I've seen installed for sewer," stated Bruce Herman, the project inspector assigned for King County. Herman elaborated on why the HOBAS pipes were so quick to install. "The push together joint installation was rapid and the joints were perfectly mated every time. The factors that permitted quick assembly were the pipe's light weight plus the fact that the joints don't leak or need repairs. Testing was easy with air pressure. We tested the whole run at once, instead of individual joints. We didn't see any loss."
Mike McGinley, project manager for Frank Coluccio Construction Co. of Seattle, WA, elaborated on the installation, "Most of the job was at moderate to shallow cover in good ground. Installation through this part went really well. Our best day was 13 pipes extending 260 feet. A portion of the job was deep and wet with poor soil conditions. Production rates were slower due to the depth but the pipe performed just fine.
"The County has taken possession of the new line and it is currently in service." This was in late June and McGinley went on to commend the service he received from HOBAS, "I personally was very pleased with the cooperation we received from your dispatch people. They were very accommodating and delivered the product on time."
With the HOBAS pipe performing well, their faith in the product is reconfirmed. All say that they would be happy to see HOBAS on another upcoming project.
HOBAS Pipe (www.hobaspipe.com) is manufactured in sizes from 18 inches to 110 inches in pressure and non-pressure classes. The company is based in Houston, TX.