2013 Northwest Trenchless Project of the Year

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Congratulations to the City of Edmonton, Michels Canada Co., and Stantec Consulting Ltd. for winning the 2013 Northwest Trenchless Project of the year!

2013 Project of the Year Poster

The Big Lake Offsite Sanitary Gravity Portion (W14) Project is a unique and challenging project for the City of Edmonton, designed by Stantec Consulting and being constructed by Michels Canada. The W14 sanitary trunk consists of 2.11 km of 1,200 mm gravity sewer installed at depths from 4 m to 9 m. The W14 trunk will convey wastewater flows from the Big Lake development in northwest Edmonton and the Winterburn Industrial area, projected to reach 13 MLD by 2024. The ground conditions along the proposed alignment are extremely poor, including a near ground water table, wet sand, peat layers, and the potential for flowing silt and hard cobbles. The alignment crosses two major high-traffic roads, as well as the new Anthony Henday Drive on-ramps. Schedule was also a concern, as sewage from the development would have to be hauled by truck until this trunk sewer was in service.

The original design was based on a traditional trenched installation. Michels tender included an alternate bid to install the trunk sewer by microtunneling, that saved the City a significant amount of money over the trenched installation tenders received. Microtunneling also allowed the alignment to be shifted from off the road to the center of 199 Street, eliminating the soft ground staging issue, which will also provide better access for future maintenance requirements. Michels also proposed the use of Hobas pipe, a centrifugally cast glassfiber reinforced pipe that is resistant to H2S attack, a condition expected to be prevalent especially in the initial years of operation with minimal upstream development contributing flow to the trunk sewer. To address the corrosion issues in the precast concrete manholes, SpectraShield® was sprayed onto all exposed surfaces in the manholes. For the major road crossings where a casing pipe is required by Alberta Transportation, Michels was able to get approval to use Permalok Pipe for the casing, which reduced the risk at these locations by eliminating the extended welding time required for a 1,500 mm steel pipe and replacing it with a push on interlocking joint. Hobas pipe was then jacked into the casing. In the areas with the poorest ground conditions (blow counts of 2 to 10), a switch from Hobas to Flowcrete Pipe was made. Flowcrete is a concrete pipe with an integrally cast FRP liner (to address the corrosion concerns) that was used to combat buoyancy. To our knowledge, this is the first installation of Flowcrete Pipe in North America.

Construction of the project began in February 2012 and is scheduled for completion in late 2013. The project was divided into 10 microtunnel drives ranging from 150 m to just over 300 m in length. Eleven sheet pile shafts were constructed, seven of which will have manhole access points constructed in them. The shafts were sized to allow jacking of 6 m lengths of Hobas and Permalok pipes behind the microtunnel boring machine (MTBM) using an 840-ton jacking frame. Michels used an Akkerman SL52 MTBM that was fitted with a second rear articulation joint to provide more steerability as a contingency in the soft ground conditions. The outside diameter of the MTBM used to install the Hobas pipe was 1,250 mm. The MTBM was “skinned up” to 1,500 mm for the sections where the Permalock and Flowcrete pipe were installed. Watertight entrance and exit seals were used at all shaft locations, and have been left in place, rather than removing and reusing the seals or attempting a chemical grouting/ground improvement program at the shaft entry/exit locations and risking ground loss. As of the writing of this article, Michels is underway on the penultimate drive and is on track to complete the project on schedule.

This challenging project has achieved a number of successes and provided the City of Edmonton with considerable cost savings over a conventional trenched installation. Microtunneling has proven to be an effective method for installation of a large diameter sanitary trunk sewer through poor ground (2 to 10 blow count) maintaining line and grade with no settlement observed to date. The innovative use of various pipe and casing materials has addressed settlement and floatation issues, while providing a sanitary trunk sewer that is resistant to corrosion and H2S attack.

Previous projects in the area were highly challenging with schedule delays and difficulty in maintaining grade. By engaging an experienced microtunneling contractor, and design team led by Stantec with Thurber (geotechnical) and SMA (risk/constructability workshop facilitation), the City has successfully completed another stage of their West Edmonton Sanitary System.

NASTT-NW would like to encourage all of its members who are conducting interesting trenchless projects to consider applying for the 2014 Northwest Trenchless Project of the Year and to take the opportunity to provide presentations of their projects at local technical lunches, the annual conference, No-Dig, and other regional events to truly highlight our region’s leadership in trenchless technology. Please watch the website and your email inbox for notices regarding the 2014 Project of the Year.