Western Europe. Pipe rehabilitation. Auger boring. CIPP works during the cold snap. Take-off by the Boeing plant. Expanding the market share

Transcription

1 Pipe rehabilitation CIPP works during the cold snap Western Europe Expanding the market share Auger boring Take-off by the Boeing plant ISSN

2 16 AUGER BORING Keeping the traffic moving Replacement of an aged water main under busy routes feeding traffic to the world s largest building called for careful planning Overview of Highway 99 distributionsystem improvement programme Construction of the project without disrupting daytime traffic to and from Boeing s plant was paramount to the overall success of the project The Alderwood Water and Wastewater District (AWWD), located roughly 20 miles (32km) north of Seattle in Washington, was formed in The area has seen rapid growth and the district now serves over 214,000 customers. In 2012, AWWD began construction of the Highway 99 distribution-system improvements that consisted of the replacement of 80-year-old water mains along Highway 99 and new pipe under State Route 525. These are two major highways carrying Boeing workers to the Everett factory (home to the world s largest building by volume, housing 42,000 employees), at an Average Daily Traffic (ADT) volume of 38,900 and 61,000 vehicles each day respectively. The basic problem is common to many utility projects: installing new or replacement water and sewer lines, while minimising both safety concerns and impacts to the motoring public. However, when the road involved is a six-lane arterial with a speed limit of 45mph (72kmph), the challenge is to avoid any daytime road interference. POTENTIAL TRAFFIC IMPACTS In 2011, the federal government, through the American Recovery and Reinvestment Act, commissioned a transportation report for the Evergreen Way/Highway 99 Revitalization Plan. The report identified Evergreen Way/ Highway 99 as a highway of regional significance within the AWWD project area. According to the 2011 Transportation Report, Highway 99 south of Airport Road currently has an ADT of 38,900 vehicles (Perteet 2011). According to the 2013 Washington State Department of Transportation (WSDOT) Annual Traffic Report, State Route 525 saw an ADT of 62,000 vehicles on average in 2013 (WSDOT 2013). Construction of the proposed project without disrupting daytime traffic to and from Boeing s plant was paramount to the overall success of the project. Boeing runs three shifts at the plants, so shift-change times had to be taken into consideration during the planning. TRENCHLESS SOLUTIONS During the preliminary design phase, in evaluating alignment and construction options, several project goals were identified: Minimise the possibility of damaging the fragile water mains during construction, failure of which would disrupt traffic and potentially undermine the road section; Avoid existing utilities where possible to minimise construction conflicts and utility relocations; Minimise water-service interruptions to businesses; Minimise surface restoration within the paved right-of-way; and Minimise traffic impacts. The risks in using the trenchless techniques included boring into unknown utilities, heaving the road, groundwater seepage, the casing veering outside of tolerances, hitting a large boulder and other more minor risks. These risks were evaluated and in light of WSDOT s stance on not allowing open-cutting the roadway for transverse crossings, the risks were deemed acceptable. The design called for the installation of three waterline crossings of Highway 99 and one crossing of State Route 525. The crossings of Highway 99 included both water-main replacements and future pressure-zone continuation. The crossing of State Route 525 was part of the concept that eliminated a significant portion of high-cost work along the east side of Highway 99 and allowed the district to eliminate additional ageing infrastructure. TRAFFIC CONTROL The overarching goal during construction, other than pipe replacement, was the safety of the travelling public and all parties involved in the project. The contractor s work hours

3 AUGER BORING 17 were different for northbound and southbound traffic and depended on whether a shoulder, one-lane, or two-lane closures were required for any given stretch of the several mile-long project. Typically, work hours with lane closures were limited to between 11pm and 5am, which did not allow much time for production. The bore-pit locations were designed to be off the used part of the road, so that work could be completed during the day for more efficient production (and lower cost) and less inconvenience to the public. Some of the tie-in excavations did require construction in the roadway, since the alignment of the water mains was in a travelled lane, and required cutting out a piece of the bore casing in the middle of the highway. CONSTRUCTION SEQUENCING The contractor had flexibility in sequencing the construction work on the highway. The district expected that two or three crews would be working at any given time on the project. Because of the way that the traffic-control work was paid (on a per-unit basis), the contractor had more crews than anticipated with many flaggers on site, so the traffic-control cost was higher than originally projected. There were many drunk-drivers observed, and a few minor incidents and near hits, with additional police presence to minimise the possibility of accidents. The sequencing of the borings was dictated in part by the general contractor s approach to the project, with the order of the bores following the contractor s work. The casings were installed during daytime work in a straightforward manner without issues, except for where contaminated soil that was discovered at one bore pit. The contamination delayed the start of the bore for several days while tests were run to determine Bore 1: Highway 99 and State Route 525 The first auger-bore crossing of Highway 99 occurred approximately 300ft (91.4m) north of the off-ramp from State Route 525 to Highway 99. This called for the installation of 115ft of 36in (914.4mm)-diameter steel casing, which would house the 12in-diameter ductile iron carrier pipe. The boring had to cross six lanes of traffic while avoiding storm, fibre-optic, phone, gas, The traffic-control cost was higher than originally projected. There were many drunkdrivers observed, and a few minor incidents and near hits The site of the project s first auger bore water, and underground and overhead power lines. The jacking pit was constructed in an existing WSDOT access road on the east side of Highway 99, while the receiving pit was built on the west side. The size of the jacking pit was limited to a 40ft by 40ft temporary construction easement. The bore was installed at a depth of approximately 14ft below Highway 99.

4 18 AUGER BORING Bore 2: Highway 99 and Russell Way Aerial view of the site for the second bore The second auger-bore crossing of Highway 99 occurred just south of Russell Way in front of a property with a busy recreational-vehicle (RV) sales business. This road crossing was unique because it required the installation of two separate carrier-pipe systems: a 12in ductile iron pipe for the 724 pressure zone, and a 16indiameter pipe for future extension of the 635 pressure zone. This was accomplished through the installation of approximately 80ft of 42in-diameter steel casing, which housed both carrier pipes. The jacking pit was again installed on the east side of Highway 99, but this time it was within the RV sales lot. Two stages in the boring process for the second bore A temporary construction easement was negotiated with the property owner and required that the contractor construct the auger bore within tight site constraints. Access to the RV lot needed to be maintained as well. The receiving pit at this crossing was located within the Highway 99 ROW, which required that the intertie be constructed at night. This crossing was installed at a depth of approximately 15ft. Each of the proposed auger bores presented its own unique challenges the contaminants and the affected soils were removed. The timing of the tie-in excavations was co-ordinated and required lane closures. This type of work was completed at night per the permit conditions. Bore 3: Highway 99 and Airport Way Third bore location The final Highway 99 crossing was just south of Airport Road. The new pipe serving the 724 pressure zone had to cross from the west side of Highway 99 to the east and then travel north along it across Airport Road in parallel with a new 12in-diameter ductile iron waterline serving the 635 pressure zone. The crossing was constructed using a 36in-diameter steel casing, 77ft long. The jacking pit AUGER-BORE CONSTRUCTION Each of the proposed auger bores presented its own unique challenges. Each of the jacking and receiving pits had to be located within the existing right of way (ROW), or additional easements Work under way on the third bore was designed on the west side of Highway 99 in a vacant lot. The receiving pit was in the eastern turn lane for Airport Road, and required night construction for the final intertie. This crossing was at a depth of approximately 14ft below the road. had to be obtained to allow for construction. The pits had to be situated so that they did not interfere with the constant traffic flow and contractors could not move or relocate existing utilities. In addition, two of the four auger-bore installations required that the contractor excavate intertie pits within the travelled lanes of Highway 99 at night to allow for the proper alignment of the proposed water installation. Each of the four auger bores is discussed in further detail in the boxes on these pages. CONCLUSION AND SUMMARY The success of this project rested heavily on the design research and details, construction sequencing, and selection of good bore and receiving pit locations. Additionally, selecting the appropriate method of trenchless construction avoided major problems during construction. The design team conducted a detailed alternatives analysis to determine the most cost-effective and least risky way of replacing the waterlines in Highway 99.

5 AUGER BORING 19 The major project risks included construction equipment or vibrations impacting the deteriorated mains, causing a major water-main break in the heavily travelled highway and protecting the safety of the participants and public during construction work, most of which occurred at night with cars speeding by. The team oversaw the installation of new waterlines to improve the pressures in the project area while minimising project risk. The effort was facilitated without affecting existing utilities or interrupting water service throughout construction. Additionally, surface restoration and traffic impacts during construction were minimised. The combined strategies allowed the AWWD to replace this critical infrastructure without significant impacts to the roughly 36,000 local customers, the near-by industries, including Boeing, or thousands of daily commuters. These important improvements are a vital section of the 660 miles of water main used to reliably deliver 9 billion gallons of potable water a year to the district s residents and businesses. Bore 4: State Route 525 The auger-bore crossing of State Route 525 was part of the low-pressure improvement phase of the project. It was developed by AWWD and Stantec staff to minimise construction on Highway 99 while eliminating additional ageing waterlines. During design it was determined that a route alternative for the replacement of the 635 pressure zone piping could reduce the need for approximately 6,000ft of pipe on Highway 99. The bore involved installing 115ft of 36in-diameter steel casing to carry a 12in-diameter ductile iron pipe across State Route 525. A jacking pit of approximately 20ft by 35ft was Views of the final crossing bore installed on the east side of the road roughly 190ft south of 149th Place SW. The receiving pit was installed in the ROW for State Route 525. The receiving pit had to be installed on a sloped area to avoid existing utilities, which complicated the work. At its deepest point, the casing was 11ft below the road. Boring under State Route 525 The effort was facilitated without affecting existing utilities or interrupting water service throughout construction This article is an edited version of AWWD uses auger boring to keep the traffic moving by Erik Waligorski and Laurie Fulton from Stantec, and Jeff Clarke and Paul Richart from Alderwood Water and Wastewater District. Original presentation given at NASTT s 2015 No-Dig Show. North American Society for Trenchless Technology. All rights reserved. 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