Posted Apr 13, 2021, 9:01 PM
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Join Date: Mar 2012
Location: Ottawa
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According to this, tunnel (or I guess trench, by that point) excavation should be completed by April 2022.
Quote:
Your Guide to Stage 2 O-Train West Extension’s Slurry Plant
Over the last few months, many Ottawa residents driving along the Sir John A. Macdonald Parkway (SJAM) may have seen what looks like an indoor golf driving range by the sight of a large white tent and two white silos (6m high) in the Kitchissippi Ward, near Cleary Avenue. The structure has nothing to do with sports. In fact, the site is called a slurry plant.
This plant is crucial to building two tunnels, key features of the O-Train’s west extension.
The three-kilometre Parkway tunnel will travel between Kichi Sibi and Lincoln Fields stations travelling underneath the SJAM and Byron Linear Park.
Construction of the tunnels has started, using a cut and cover technique, which in non-construction terms, is a top-down technique rather than a drilling method. Cut and cover construction involves using excavation equipment to dig a large trench or rectangular hole in the ground which is then covered by a concrete deck. Once the deck is in place, surface activity can largely resume as construction crews continue to work below.
What makes the tunnels unique is the use of slurry walls to support the excavation while digging proceeds. If crews just started digging, water and sand in the area would cause the new excavation to cave-in. These special walls made of mixture of bentonite (a type of clay), water, and cement with steel beams placed inside for strength are waterproof and strong enough to keep the hole from caving in when the crews dig the remaining area of the tunnel between the slurry walls.
As the dirt is dug out, it is replaced by slurry which is pumped from the slurry plant to where the digging is occurring through a series of pipes. The weight of the slurry keeps the hole from caving in. The wall is built with a series of panels, hop-scotched, at about one to two panels per day. When a panel is excavated and filled with slurry, steel beams are installed in the wet slurry. In a couple of days, the slurry dries and hardens (just like concrete) and then a portion of the slurry wall is complete. The process then repeats itself to continue to construct more walls.
When the crane continues to dig through the hole, it puts the excavated material (which contains a mixture of soil, bentonite, cement, dirt, water) into a dump truck which then hauls it to a storage and drying area called slurry pits at Rochester Field near the plant location. The slurry waste is left to dry before being trucked to the Trail Road landfill site.
The slurry wall technique was first introduced during the excavation of the underground rapid transit system in Milan, Italy just after the end of World War II. This new technology became an important component of the top-down tunneling method also known as Metodo Milano ("Milan method"). It made its first rail construction appearance in North America in the 1980s when the Boston subway’s Red Line Northwest Extension project used the modern form of the technology.
Slurry will be mixed in this dedicated plant onsite and the slurry plant will be operational until approximately Spring 2022 when it’s anticipated slurry walls for the tunnels will be fully built.
The current slurry plant visible with two white cement silos and a large white tent. The large tent covers tanks, pumps, and other equipment used to produce slurry.
Aerial westbound view of the slurry plant. It will be operational until approximately April 2022.
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https://ottawa.ca/en/planning-developmen...xtension-spring-2021-information-session
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