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Western Alberta Transmission Line Civil Foundations Langdon Bennett Substation

Western Alberta Transmission Line Civil Foundations Langdon Bennett Substation
Date: 2013

In the expansion of the existing Langdon electrical substation, general contractor PCL Construction Management Inc. engaged Agra for the foundation work of the project. AGRA Foundations Limited installed 500 bored concrete piles, the majority of which were installed using the CFA method. The ground profile was composed of silty clay up to 6 m deep overlying silty, dense sand overlying bedrock at varying depths up to 13.0 m deep. Sub artesian water pressures were encountered, posing additional challenges to the construction process. The majority of the CFA piles were 600 mm and 750 mm in diameter and varied in depth from 9.5 m to 13 m below grade. AGRA also installed 50 large diameter bored concrete piles with diameters of 1500 mm to 1800 mm, 9.5 m to 13 m below grade. Large diameter piles were formed with 3.0 – 5.0 m long rock sockets. The rock was fractured and wet, so the piles were concreted with a tremie pipe.

Solution:

The AGRA team used three heavy duty piling rigs for this project. Two rigs were able to install about 20 CFA piles daily. The method proved to be ideal for the ground conditions and the piles were efficiently drilled into the bedrock and concreted in one operation. The third crew were installing large 1.5 and 1.8 m diameter piles which filled with water and could not be sealed off with casing. AGRA bored the pile under water with our specially designed drilling tools and cleaned the base of the pile. The heavy reinforcement cage was placed by a service crane followed by a full-length tremie pipe. The pile was concreted with a free flowing concrete mix and the displaced water was pumped away with a Hydrovac truck.