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February 1, 2000

Months of planning for 13 seconds

Journal Construction editor

What do you do when a 25,000-ton concrete roof comes crashing down? Figuring that out is one of the tasks facing those in charge of demolishing the Kingdome.

The impact of the Dome's concrete roof falling as much as 250 feet is just one part of a demolition plan for the stadium that has been submitted to the city. Once the button is pushed, the Dome will come down in 13 seconds, but planning and preparing for that event has taken months.

According to the plan, the stadium will be imploded and razed in four phases. Sources put the cost at $9 million. The implosion date has not been set, but is expected to be a Sunday morning in late March or early April.

Kingdome drilling
Crews from Pacific Blasting drill holes for explosives that will be used to demolish the Kingdome.
After the Dome comes down, about 35 percent of its 110,000 tons of concrete will be recycled for the new stadium through an on-site crushing plant. The rest will be sold as fill and trucked off. The spokesman said no buyers have been lined up yet.

The first phase started Dec. 30 and will last until four weeks before implosion. It includes vibration testing of surrounding structures by Schnabel Engineering of Bethesda, Md. Officials expect the vibration could cause minor cosmetic cracking of interior drywall in smaller buildings near the Dome. Also under study is what vibrations could do to the Fourth Avenue South bridge.

Local engineering firm Skilling Ward Magnusson Barkshire is developing a third-party review of the vibration studies.

The second phase of demolition continues until just two hours before implosion. It includes getting permits from the Seattle Fire Department for explosives handling, from SeaTran for street use and from the state Department of Transportation to reroute traffic. Also, the director of the city's Department of Construction and Land Use will need to give his approval.

The third phase runs up until the "all clear" signal is sounded for blasting. At that point, approvals will be needed from the police department, fire department, DOT, State Patrol, Burlington Northern Railroad and Amtrak.

The last phase involves post-blast cleanup, and it will require a crushing permit from the Puget Sound Air Pollution Control Agency and complying with city noise ordinances. The plan states concrete rubble crushing will begin at the eastern edge of the rubble pile and move west.

Many months of planning have gone into the demolition plan.

Preparing the Dome for its doom includes removing a 6-inch membrane from the 40 concrete ribs that make up its roof. That is being done by TLH Abatement to keep contaminates out of the concrete so it can be recycled.

Kingdome safety zone
This map shows the proposed safety zone around the Kingdome on implosion day.
Debris from the top of the roof is being dropped through the roof hatch and down a debris chute to the center of the field inside. Debris from the upper 90 feet of each roof bay is being dropped into the center chute through the ventilation grill area. Remaining debris from the lower sections of the bays is being fed through openings to the inside of the building.

Some of the Dome's exterior and interior precast concrete ramps will be removed before implosion. They will be removed by small excavators on the upper levels and larger equipment at the lower levels. Also, precast concrete bleacher sections at the lower level will be removed prior to implosion.

It seems no detail has been overlooked in preparing the Dome for demolition. For example, fluorescent lights are to be removed and any PCB-containing ballasts disposed of in the proper fashion. Even mercury-containing fixtures, like thermostats, have a disposal plan.

Some of the components of the Dome will be used to help shield nearby structures from the blast. The prefabricated mechanical rooms that circle the outside of the Dome will be removed by crane and stacked two-high along Occidental Avenue South to create a 400-by-24-foot sound and dust barrier. After the blast, the mechanical rooms will be hauled to a recycling facility.

Buildings adjacent to the Dome are being prepared too. Olympic Reprographics will have its air-handling units sealed, door and window seams taped, and the east face of the building will be draped in geotextile fabric. Olympic also will be provided with poly sheeting to drape over inside equipment for dust protection. Some businesses in the area will have their doors and windows covered with plywood.

Controlled Demolition Inc. of Phoenix, Md., and Aman Environmental Construction of Covina, Calif., are the main contractors in charge of demolishing and imploding the Dome. Since no big concrete domed stadium has been imploded before, Schnabel looked through CDI's historical database on vibration effects from past projects. It found seven past demolition projects that had similar characteristics to the Kingdome: structure size, weight and construction (140-240 feet tall, about 25,000 tons of above-ground weight and/or structural concrete); debris falling from a similar height (140 feet or higher); and a similar geologic environment (water table within 10 feet of the surface, loose saturated sand and reclaimed land).

The seven past CDI projects were: Geneva Towers in San Francisco (imploded in 1999), Neumaier Hall in Moorhead, Minn. (1999), Farmer's Export Headhouse in Galveston, Texas (1978), Landmark Hotel in Las Vegas (1995), Jack Frost building in Philadelphia (1997), King David Hotel in Atlantic City, N.J. (1998), and the Hudson Building in Detroit (1998). All of those projects met industry standards for vibrations caused by their implosions.

Chuck Wilton of Scientific Services of Redwood City, Calif., is serving as a consultant for the implosion plan. Locally, Wilton has been involved with the demolition of the Harper & Great Western Building (1984), Olympic National Life Building (1984), Savoy Hotel (1986) and the Asarco smokestack in Tacoma (1993).

Ramp view
Parts of the Kingdome's ramps will be removed prior to implosion.
A letter from Wilton in the demolition plans says loading and preparing the explosives in the Dome will take 15-18 days. Holes for the explosives are now being drilled by Pacific Blasting of British Columbia. They are expected to be finished later this month.

Details about how much explosives will be used and where they will be placed were not included with the plan submitted to the city. CDI and Aman said some of the procedures are trade secrets -- such as the type of explosives, where they will be stored prior to placement, and the explosion sequence/delay pattern.

The plan did say explosives will be placed in the roof in such a way as to fragment the roof into sections weighing less than 15 tons.

A spokesman said there will be no ceremony involved in the implosion and a CDI worker will push the button.

The entire implosion spectacle will be recorded by the British Broadcasting Corporation, which bought the rights to film it for $25,000 from the Washington State Film Office. The BBC has filmed several of CDI's past projects.

Clearing the site for new construction should take four to six months. The new stadium is expected to be complete July 2002. Turner Construction is the general contractor building the new stadium for the Washington State Public Stadium Authority


Benjamin Minnick can be reached by email or by phone at (206) 622-8272.

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