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Crews dig deep to bolster AC Hotel site at Terminal 1

Construction work has been underway for months at Terminal 1’s Block D, the future site of the AC Hotel by Marriott. So far, the work has focused on preparing the ground beneath the site by sinking hundreds of pilings into the soil to support the weight of the future structures above.

There’s just one hiccup: Someone else did the same thing more than a century ago, and they never took the old pilings out.

The G.M. Standifer Construction Corp. built the Standifer Shipyard at the future Block D site in 1917 to churn out wooden and steel cargo ships during World War I — a massive project that spurred much of the Port of Vancouver’s early industrial development.

“It would make this (hotel) project seem tiny,” said port project delivery manager Mark Newell.

The shipyard needed a foundation, and that foundation needed pilings. Modern construction techniques use cement grout to form the pilings; but back then, the state-of-the-art fix was to float hundreds of logs down the river to the site and hammer them into the ground.

The port owns the Terminal 1 site and is spearheading the overall redevelopment project. Newell said port officials knew the ground would need to be stabilized before any new structure could be built, and they knew they would need to contend with some old pilings first.

But there weren’t any design records from a century ago, Newell said, only historical photos of the shipyard, so the crews from contractor Keller North America didn’t know the extent of the problem until they began digging. Work on the modern pilings ended up having to be paused so crews could focus entirely on removing the old ones.

“(In) December, they really went at the piles primarily,” Newell said. “There turned out to be a lot more of them than we thought.”

In the end, the crews pulled out 712 of the old wooden logs. The process pushed the price tag for the ground stabilization up from about $2 million to closer to $5 million, according to Newell and Keller superintendent Walt Nalty.

Considering they’ve been stuck underground in wet soil for 103 years, the old wooden pilings are in surprisingly good shape — many of them still had bark on the outside, Nalty said, and port executive project sponsor Jonathan Eder said the port thinks some of them could be turned into usable lumber.

(Fun fact: The pillars that support the Interstate 5 Bridge sit on top of similar centenarian pilings, so the resilience of the wood is reassuring).

Crews extracted the wooden pilings by digging down enough to allow a machine to grasp the top of each piling, then vibrated them to loosen them from the ground. The strength of the wood was helpful — port communications director Heather Stebbings said there were initial concerns that the logs might snap during the extraction, but most of them stayed in one piece.

The extraction work wrapped up in January, and now crews have been able to turn their attention back to the new pilings. That work is expected to be completed within four weeks, and then the job site will quickly segue into construction of the hotel foundation.

The new pilings are arranged in a gridlike structure of dense rows, carefully coordinated to align with the future positions of the hotel’s load-bearing walls and heavier sections such as elevators shafts. Additional clusters of pilings are sunk into the gaps in between, which will help counteract possible soil liquefaction in the event of a major earthquake.

“These ones are a little bit stronger (than the wood ones), to say the least,” Newell said. They also go much deeper into the ground, pushing down about 30 to 50 feet to hit bedrock, compared with about 20 feet for the original wooden pilings.

The crews are using a single drilling rig to install all of the pilings, but it’s a fast process — by necessity, since it involves wet cement. The rig powers a custom drill bit that’s designed to simultaneously dig a shaft and inject it with a cement mix pumped in through a pipe.

The custom drill is only really meant for digging through soil, Newell said, so when the crew encounters a large rock or other obstacle, they have to pause and install a heavy-duty auger to punch through.

“(The auger) is an actual drill bit,” Nalty said. “(The injection bit) is more of an egg beater.”

Digging proceeds at about three feet per minute, Nalty said, with the drill head filling the shaft as it goes. Once it reaches the full depth, it reverses back out through the still-wet cement mix, leaving behind a full piling that will solidify in a matter of hours, then it’s rinse-and-repeat; reposition the rig and start drilling the next hole.

The pace allows the crew to get through as many as 20 pilings per day, Nalty said, but the process still takes weeks because they have to install about 650 in total — almost enough to replace their wooden predecessors piling for piling.

“We’re going through about 160 tons of cement a day,” Nalty said.

The AC Hotel by Marriott is being built by Vancouver-based developer Vesta Hospitality. When completed, the seven-story building will feature 150 guest rooms and 4,000 square feet of meeting space, with an internal parking garage on the second and third floors. The hotel is targeting a November 2021 completion date, Eder said.


Source: https://www.columbian.com

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