327ft Guyed Tower Converted from Concrete to Helical Pile Foundation

Client: Bell MTS
Location: Lac Du Bonnet, MB
Foundation Loads: 14kN [3.1kips] Shear and 1,846.6kN [415kips] Axial
Anchor Loads: 563.3kN [126.6kips] Uplift and 609.4kN [137kips] Axial
Refusal: End Bearing, Very Dense Till at +/- 37'-6"
Key Hurdles: Extremely saturated site

 

PROBLEM: VersaPile was engaged prior to construction by Bell MTS to support a 99.8m [327ft] communications guyed tower to bring 5G cellular voice and data service to the surrounding community of Lac Du Bonnet, Manitoba. The geotechnical investigation conducted by Wood encountered auger refusal at 11.4m [37'-6"ft] depth in till consisting of N values in excess of 30 with sloughing and seepage observed from 2.6m to 3.1m as well as 10.4m to 10.7m.

The original foundation solution was a concrete foundation consisting of a 6ft x 38ft caisson for the centre tower and three massive deadman anchor blocks with 26ft anchor channels.

The project was to be completed in the summer of 2022 following record breaking levels of precipitation in the area. This meant that the site, which already experienced sloughing and seepage, was very saturated. To complete the project with concrete meant additional site preparation, rig matting as well as major de-watering efforts. In addition to these potentially significant price escalations, concrete foundation contractors in the area were behind in scheduling due to the consistent rain and already saturated soils in the area.

The Client, who had never built a 100m (327ft) guyed tower on anything but a concrete foundation, reluctantly brought the project to VersaPile Inc. to consider helical piles.

SOLUTION: VersaPile engaged Cory Goulet P.Eng. of Pilisk Geostructural to analyze soils and tower design to engineer an alternative foundation solution using helical piles.

The solution was to replace the large concrete caisson under the tower with a 4 pile grouping of helical piles installed on opposing 10 degree batters. The massive concrete deadmen anchors were replaced each with a single helical pile installed on a 42.8 degree batter.

CONCLUSION: VersaPile, with a team of project engineers, installed 7 helical piles with pile caps site welded by Reg Dumont of DC Custom Welding. The project was completed successfully despite the challenging marsh like conditions. The centre piles were installed using VersaPile's CASE CX350 with Digga UD300 anchor drive, while the more difficult guy-anchor locations were accessed by the lighter John Deere 290G with Eskridge D1400 anchor drive.

The Client was very satisfied with the results and would no longer be reluctant to construct tall guyed towers on helical piles. They realized savings in excess of $225,000 to the budget and avoided the many potential cost escalations related to digging, drilling and working in sloughing and seeping soils. The timeline for the project was reduced by at least 2 weeks and likely longer as water would have surely slowed down typical production times.

There was also a HUGE savings in carbon emissions on the project. The conversion of a concrete foundation to a helical pile foundation resulted in a 98.3% reduction in CO2 emissions. This means that 60 helical pile foundations could be installed to equal the same amount of GHG emissions as the originally proposed concrete foundation.

 

CASE HIGHLIGHTS:

4 PILE GROUPING TOWER

• 219mm [8-5/8"] Ø shaft, 8.2mm [0.322"] thick wall, 660mm [26"] double helix at 25mm [1"] thickness
• +/- 11.4m [37'-6"] depth to refusal
• 45.7 kip-ft [62 kN-m] torque

 

3 - ANCHOR PILES

• 219mm [8-5/8"] Ø shaft, 13mm [0.5"] thick wall, 660mm [26"] double helix at 32mm [1-1/4"] thickness
• +/- 16.8m [55'] depth to refusal
• 82 kip-ft [111 kN-m] torque

Installed with:

• CASE 350 (40T Excavator)
• Digga UD300 anchor drive
• John Deere 290G (33T Excavator)
• Eskridge D1400 anchor drive
• Support with New Holland C245 Tracked Loader with grapple

 

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