2014 Northwest Trenchless Project of the Year

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Congratulations to the Regional Municipality of Wood Buffalo, Associated Engineering, Michels Canada Co., Neptune Coring, Direct Horizontal Drilling, Calgary Tunneling, and Horizontal Augering on being awarded the 2014 Northwest Trenchless Project of the Year for the Saline Creek Plateau Offsite Water & Sewer Servicing!

2014 POTY Poster

 

Project Details

The Regional Municipality of Wood Buffalo recently expanded its water and sewer infrastructure to service the new Saline Creek Plateau residential development in the City of Fort McMurray, Canada. The project commenced in 2008 and consisted of 3km of 600mm transmission main, 10km of 750mm water supply line, and 3km of 250mm and 700mm double barrel sanitary sewer siphons. The project team faced many challenges, including a complex topography, proximity to existing infrastructure, and the presence of water courses along the alignment., As a result, the project required extensive use of trenchless installation technology including pipe ramming, auger boring, and horizontal directional drilling (HDD). The following is a summary of the four key crossings along the alignment:

Hangingstone River Pipe Ram and HDD

The Hangingstone River has a relatively short span, however, the underlying geotechnical conditions consist of a deep layer of sand and gravel overtop of limestone. Geotechnical and tie-in limitations required two 900mm diameter and one 600mm diameter steel pipes to be installed over a span of 95m via pipe ram. Initially, the 600mm diameter steel pipe ram was attempted. However due to the geotechnical conditions it was aborted. Since the carrier pipe inside the aborted 600mm diameter steel crossing was 450mm HDPE, a 150m long HDD was proposed and successfully completed.

Saline Creek Valley HDD

The Saline Creek Valley spans 600m in length between the top of the banks and separates two steep, unstable valley slopes with Saline Creek, located at the bottom of the valley. The geotechnical conditions along the valley slope consist of clay till, sand, gravel, silt, clay/silt in varying thicknesses overlying bedrock consisting of clay shale, siltstone, and sandstone overtop of oil sand. Due to the unstable nature of the valley slopes, combined with the required top of bank setbacks, and the limiting bend radius geometry of the steel piping, the total crossing length was 1000m. Two pipes, 600mm and 750mm diameter steel, were installed in parallel.

Tower Site Auger Crossings

A narrow right-of-way and the presence of clustered communication towers required installing two 1500mm, 8m deep on grade (1%), auger crossings over 70m, and two 1050mm, 5m deep, auger crossings over 70m. The ground conditions consisted of gravel with large boulders presenting steering challenges and multiple auger flight twist offs.

Clearwater Valley Slope HDD

The most challenging of the trenchless installations was the unstable Clearwater valley slope HDD of 300mm, 700mm, and 750mm steel piping, 80.0m below the ground surface, extending over 1300m through the oil sands and up to the top of the plateau located 130m above the HDD entry. Deep layers of silts and sands at the entry point required over 100m of surface casing and steeper entry angles for all three drills. The pipeline drag alignment required threading the piping between the top of bank slope on one side and congested communication towers on the other side. This necessitated tight radiuses for the above ground support equipment.

Why Project is Outstanding
The challenging geotechnical conditions and varying terrain required designing four multiple pipe trenchless installations with various diameters, lengths, and methods. Prior to this project, the Municipality had limited experience with trenchless installations outside of the typical short span highway auger crossing or 100m small diameter directional drilling. The Municipality is expanding very quickly with new development areas that are separated by major creeks and valleys with challenging geotechnical conditions presenting long-term risk to the infrastructure being installed.

The trenchless installation work was completed by four different, reputable, and experienced contractors.. This led to the successful completion of the work on time and without major disruptions.

The two 900mm diameter and one 600mm diameter pipe rams across the Hangingstone River required the ramming equipment to be set up 10m below the existing ground elevation and 6m below the river elevation. This required an extensive well point dewatering system and shored excavation to protect the river banks. Telescopic pipe ramming was considered, however, the contractor determined large ramming equipment and heavy wall steel pipe was a more effective solution. The presence of what was thought to be old timbers, caused the aborting of the installation of the third 600mm diameter pipe ram.. However, HDD was adopted as a suitable alternate method for this third pipe crossing.

To limit risk to the project, the project team decided the drilling contractors must be pre-qualified in advance of public tender to ensure that the work would be completed by experienced contractors.. This approach proved to be valuable in retaining competent contractors to complete the work. The pre-qualifying process also allowed the Municipality and its consultants to evaluate the expertise of the contractors based on past performance and personnel, and not solely on tender pricing.

The Clearwater Valley slope and Saline Creek Valley piping was installed through rich oilsands deposits that contaminated the drill cuttings. This environment required drilling fluid additives to cut the grease and build up on the shaker screens, where possible. The proposed additives were not able to be used for the Saline Creek crossing and therefore the contractor was forced to continually replace screens. The final disposal of nearly 20,000m3 of contaminated drill cuttings proved to be challenging. However, varying levels of treatment were developed by the project team, owner and contractor to ensure environmental standards were met.

The Saline Creek Plateau Offsite Water and Sewer project has provided the Municipality with the confidence they needed to move forward with future trenchless installations. As a result, additional designs for installations have been implemented on other projects, based on the success of this Saline Creek Plateau Offsite Water & Sewer Servicing project. The design effort, coordination, and collaboration between the contractors, owner and engineering consultant has created greater opportunities in municipal market for future large diameter installations.