Work piles on to make new school earthquake proof

MARYSVILLE Workers are driving more than 250 concrete piles 60 feet into the soil at the Grove Elementary School construction site to make the new, two-story building safer in earthquakes.

  • Thursday, August 28, 2008 11:47am
  • News

A construction crew from McDowell Northwest uses a huge crane to bore one of 257 holes into the ground last week at the site of the Marysville School Districts new elementary school. Each one of the 60-foot-deep holes will be filled with a rebar cage and concrete to create hundred of stilts to support the slab floor in case of an earthquake.

MARYSVILLE Workers are driving more than 250 concrete piles 60 feet into the soil at the Grove Elementary School construction site to make the new, two-story building safer in earthquakes.
The 54,000-square-foot structure will house up to 550 students plus additional staff and visitors, and engineers stipulated the need for 257 pilings to support the concrete floors in case of a temblor.
A crew from McDowell Northwest Inc. is using a huge crane to make the auger cast pilings deep in the ground at the intersection of Grove Street and 67th Avenue NE.
You either need to excavate down to the good soil or drive piles down to it, explained Bruce McDowell, company vice president and general manager. Its a fairly large job.
Pilings have been used as supports for buildings since the middle ages, he added, and his company is working on a wastewater treatment plant in Mount Vernon that will require more than 600 pilings. In the auger cast piling technique a big drill head measuring 18-inches in diameter, with a hollow center, is pushed and twisted into the earth. As it delves deeper into the soil a cement-based grout is pumped at high pressure through the hollow tip. As the auger drills the soil the grout pushes the loose dirt up through the remaining hole, so engineers and geologists can inspect the spoils brought back up as the auger is slowly withdrawn from the hole.
The holes at the Grove site are 18 inches in diameter and go down 60 feet. After they are filled with concrete a 30-foot-long steel cage made of reinforcing bar is vibrated into the pile, with a central steel beam or bar going all the way to the bottom. In some sites the rebar cage is installed first and concrete is poured around it. The piles will stick out of the ground and an eight-inch-thick concrete slab will be poured around and over them, with rebar throughout, said Clint Bjella, project manager for general contractor Allied Construction of Everett.
This basically ties it down to solid ground so its not going anywhere, Bjella said.
The main fear is that in an earthquake the soil underneath the school could liquefy and damage the building, according to Marysville building inspector John Dorcas. A school has to be designed and engineered more thoroughly than many other structures, he said, noting that when an occupant load gets above a certain number additional safeguards have to be put in.
The soil is a little soft there, thats why the engineers designed it with the auger cast piling, Dorcas explained.
District superintendent Larry Nyland said his office has been getting many calls from people asking if crews are drilling for oil at the site.
That building is the safest building in Marysville if there is an earthquake, Nyland told the school board on Aug. 6.

Marysville Getchell High School on track for 2010
Administrators plan on committing the Marysville School District to a 2010 opening for a new 1,600-student high school, according to capital projects director John Bingham. The $79 million high school was the center piece and crown jewel of a $118 million bond package approved by voters in February 2006 and will be designed to accommodate four of the new smaller learning communities opening this fall. Bingham convinced the school board to take advantage of a state program that still uses the competitive bidding process while allowing districts to bring a general contractor on board much earlier.
That gives the general and subcontractors more input on how the building is designed, and keeps architects and engineers appraised of the most efficient techniques they can use. Bids usually come in much lower because subcontractors are much more confident they can do the just as specified, according to Bingham. Savings on past projects for other school districts have approached 20 percent in some cases, and thats especially important as inflation plague the entire construction industry, effecting both materials and labor.
In addition to the new $20 million elementary school, and the new Marysville Getchell High School, both funded with property taxes, the district is also building a new shared options campus for three schools on a site next to Quil Ceda Elementary School on the Tulalip Indian Reservation. That campus is funded by mitigation fees levied on new homes built in the 72-square-mile district, and will cost about $24 million and house 700 students in three independent schools.
Construction crews have already created a huge pile of topsoil and sand at the site on 27th Avenue NE, and much of that will be used for other district projects or sold, according to Bingham. Most of the needed areas on the 40-acre campus have been cleared and crews will be pouring footings and foundations for the modular buildings which will comprise the three main buildings on the shared campus. Those structures will be joined by a 12,000-square-foot conventionally built gymnasium and cafeteria that will be shared by the three tenants when the campus opens this September.
The Marysville Arts & Technology High School was scheduled to move into its new quarters after the beginning of the school year, but delays have pushed opening back at least a month for A&T. The Tulalip Heritage High School and the 10th Street Program, a small middle school, will have to wait until later in the year to occupy their new digs.
The modular buildings for A&T are mostly complete and sitting at the Williams Scotsman factory on Smokey Point Boulevard, Bingham said. They will be trucked to the site and installed starting sometime in the next two weeks, he added.

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