Communications Tower in Very Dense Soils of Rural Manitoba

Client: Xplornet
Location: Harold Lake, Manitoba (RM of Lakeshore)
Capacity: 1,434kN [195kips] ULS,f per leg compression | 1,375kN [308kips] ULS,f per leg uplift
Refusal: End Bearing, Very Dense Till
Key Hurdles: Very Dense Till at 4.9m [16ft]

PROBLEM: VersaPile was engaged prior to construction by Xplornet to support a 46m [150ft] communications tower to bring rural high speed internet to the surrounding community of Harold Lake, Manitoba. The geotechnical investigation encountered SPT refusal at 4.9m [16ft] depth with very dense soils with N values in excess of 50 from 2.5m. The client's strong preference for foundation type for this project was helical piles but the very dense soils meant the minimum embedment of 4.9m would prove challenging.

VersaPile was told by a seasoned helical pile company with extensive experience in the utility sector that the soils were too dense to achieve the desired results with helical piles - however, the client was determined and VersaPile was up to the challenge.

The alternative foundation of a large concrete pad is much less desired by companies such as Xplornet who often lease land for communications towers. The helical piles are, in general, less expensive than concrete pads, especially in rural locations, but also far easier to uninstall and fully remediate leased lands when leases expire and towers are decommissioned.

SOLUTION: VersaPile engaged Cory Goulet P.Eng. of Pilisk Geostructural as well as Silvestre S. Urbano of SSU Geotechnical Engineering to analyze soils and helical pile design options to engineer a solution that would survive the installation to minimum embedment as well as satisfy the design criteria.

The solution was to engineer larger piles which could withstand high torques as well as gain resistance in friction. In addition to the more robust piles, VersaPile designed a high torque 152mm [6in.] predrill bit equal to 56% of the diameter of the pile shaft which was utilized to pre-drill through dense soils layers, reducing the installation resistance without compromising the performance.

Furthermore, the typical 115ft-kip drive VersaPile might mobilize for tower projects was swapped out for the larger Digga UD300 producing up to 226ft-kip torque.

CONCLUSION: VersaPile, with a team of project engineers, installed 6 piles, 2 per leg which were welded I-beam pile caps by Reg Dumont of DC Custom Welding. The project which was deemed not possible was made possible and the less desirable and more expensive concrete pad foundation was avoided.

CASE HIGHLIGHTS:

6 - COMMUNICATIONS TOWER

• 1,434kN [195kips] ULS,f per leg compression | 1,375kN [308kips] ULS,f per leg uplift
• 273mm [10-3/4"] Ø shaft, 13mm [1/2"] thick wall, 607mm [24"] double helix
• 4.9m [16'] depth to refusal
• 180 kip-ft [244 kN-m] torque

Installed with:

• CASE 350 (40T Excavator)
• Custom 152mm [6in.] high torque predrill bit
• Digga UD300 anchor drive
• Support with New Holland C245 Tracked Loader with grapple

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