Visitors to Vancouver’s waterfront on Saturday likely noticed the constant stream of cement mixer trucks coming in on Columbia Way. They were all bound for The Waterfront Vancouver’s block 4, the future site of the Hotel Indigo and Kirkland Tower.
The 11-story building broke ground earlier this year, and has now reached a key turning point. After months of digging downward, construction crews will finally be able to start building upward, starting with Saturday’s placement of a massive concrete slab at the base of what is currently a 38-foot-deep pit at the building site.
“This is the big milestone,” says Nicholas Lilly, chief operating officer of Kirkland Development.
When completed in 2020, the eight-story hotel and 12-story condo tower will include four restaurants and 17,000 square feet of retail space on the ground floor. They’ll share a two-level, 206-space underground parking garage, including vertical stacked parking.
Getting to the bottom
A few days before the pour, Lilly and Kirkland CEO Dean Kirkland stand at the edge of the pit, watching as a crew of workers push themselves around on makeshift rafts floating on top of 8 feet of water at the bottom. They’re busy cleaning out large chunks of floating debris and guiding a bulldozer operator on the surface as he maneuvers the long arm down into the pit to scrape dirt off of the steel walls.
The walls form a permanent watertight cofferdam, similar to how crews build bridge support foundations in riverbeds, Kirkland says. That approach isn’t always necessary for buildings with shallower foundations, but it was unavoidable in this case because the hotel and tower needed two levels of underground parking.
“The only place to put parking is down,” Kirkland says. “(But) once you got past 25 feet, you couldn’t obtain a system that would keep the water out.”
Lilly recounts the five-month process that brought the project to this point. Crews started back in June by hammering the ring of 55-foot-tall steel cofferdam walls deep into the ground around the perimeter of the future building foundation. Then the dirt in the center was excavated, digging down to make room for the building’s two levels of parking. The elaborate process was needed to prevent the intrusion of Columbia riverwater.
As the digging reached lower, the shoring walls were anchored into place by a series of tieback cables attached to steel beams mounted around the interior perimeter of the walls. The cables pass through the steel and extend 65 feet back into the surrounding dirt at a slightly downward angle, holding the walls in place.
The walls will eventually be held up by the building’s concrete foundation, Lilly explains, but until the foundation is in place, the tiebacks are necessary to keep the pit from caving in on itself.
Fully excavated, the gravel-covered bottom of the pit is 4 feet below sea level. The cofferdam walls will keep water from seeping into the parking garage once the building is complete, but during the excavation process water inevitably seeps into the pit from below, leading to the buildup of the 8-foot-deep pool.
That’s why the construction process started in June, Kirkland says. It was timed so the pit would reach its deepest point at the time of year when the river is naturally at its lowest, making it easier to complete the excavation and the base slab pour.
“If we hadn’t made this (midfall window), that would’ve been a problem,” he says.
The big pour
The concrete layer covers the entire bottom of the pit, extending wall-to-wall and forming a seal to prevent water seepage. The slab also has to be heavy enough to withstand the hydrostatic pressure of the water underneath without becoming dislodged, Lilly says, which is why it’s 5 feet thick.
“It’s a concrete plug,” he says.
Water exposure can mar the surface finish of concrete, Kirkland says, so construction crews try to avoid pouring things like sidewalks when it’s raining. But water doesn’t interfere with the chemical reaction that actually forms the concrete, so the water in the pit didn’t have to be removed before the pour. The concrete stays at the bottom and cures over the following four days, Lilly says.
Once the slab has cured, the 2 million gallons of water on top will all be pumped out and hauled off for treatment, Lilly says, likely at some point later this week. Some dirt and debris will inevitably be left on the walls and base slab, he says, so crews will have to spend a short time cleaning out the pit before proceeding with construction.
In order to form the seal, the entire base slab had to be poured in one shot. Four pumps attached to two boom arms pushed the raw concrete through for 16 hours straight, Lilly says, starting at the center of the pit and moving outward.
Throughout the day, crews on the rafts down in the pit guided the boom arms to evenly spread the concrete. The raw material was pumped through the arms and straight down through a pipe to an exit at the bottom of the water, a method of underwater concrete work called a tremie pour.
The pumps needed to be supplied with more than 7,000 cubic yards of concrete, Lilly says, delivered in approximately 640 individual concrete mixer truckloads throughout the operation. Some of the streets near the site needed to be closed to ensure a regular arrival interval for the trucks, which is part of why the operation started at 2 a.m. on a weekend.
“The challenge is always getting the trucks emptied into the hopper in a timely manner,” Lilly says. “It can only happen on a Saturday morning.”
The trucks arrived from three separate CalPortland batch plants in order to support the volume of concrete being delivered, Lilly says. The incoming concrete also had to be inspected and tested at 150-yard intervals to make sure the quality remained consistent throughout the pour.
“It went off without a glitch,” Kirkland said on Monday. “We’re pleased we made our timeline.”
The plug slab is only the first layer of the building’s foundation, according to Lilly. An additional 6 feet of concrete will eventually be poured on top, with embedded rebar protruding out the top to anchor additional concrete in the building’s structure.
A tower crane is scheduled to be installed at the site on Dec. 4, Kirkland says, in order to finish out the subgrade levels and begin work on the building’s upper floors.
“We’ve got about three months of work before we get back to street level,” Lilly said.
