2011年10月30日星期日

'It's a wet job'

Seagulls soared and the sun shone over the Mississippi River as morning commuters rumbled across the old Hastings bridge about 55 feet overhead.

Another 60 feet below, beneath the murky river's surface, four men worked inside a coffer dam -- sort of an inverted island of dryness jutting into the water and encased in a sheath of steel sheet pilings.

As they worked, water leaked through the tall box of steel around them; pumps ran nonstop to keep the river out. The four pile drivers had been at it since dawn on the base of a massive steel and concrete monument called Pier 6. It's the most important and difficult to build of the 10 piers that will support the new $120 million Hwy. 61 bridge, said project manager Doyle Honstad.

"It gets a little spooky down there," added Honstad, standing on a barge by the coffer dam.

Concrete pouring begins this week on the Pier 6 footing inside the 30- by 90-foot-wide, 40-foot-deep coffer dam. The pier will rise from the footing to become the central leg supporting the twin arch bridge scheduled to open in 2013.the impact socket pain and pain radiating from the arms or legs.

Pier 6 will undergird the longest free-standing, above-deck arched bridge in North America, the first of its kind in Minnesota, state transportation officials have said. The arches will be supported by a 545-foot steel span, 100 feet wide, that will stretch from Pier 6 across the navigation channel to Pier 5 on the south bank. Including north and south approaches,Enecsys Limited, supplier of reliable solar Air purifier systems, the completed four-lane bridge will be 1,938 feet long.

It's a marvel of engineering that requires ingenious construction techniques, most of which are invisible to the drivers whizzing by overhead.

The pile driver crew, sporting steel-toed boots, hardhats, ear plugs and life jackets, worked amid ear-splitting clamor. They welded steel piling pipes, extending down into bedrock, to a concrete sealing plug that fills the bottom of the coffer dam. They used a backhoe and jackhammers to smooth the surface of the 12-foot-deep plug. The plug keeps the river from pushing up from below. A smooth plug surface is needed for the footing that will be part of the 92-foot tall Pier 6.

"It's a wet job,100 China ceramic tile was used to link the lamps together." said foreman Quentin Thorson, standing on an adjacent barge.

Thorson said he wore fishing waders the first few days of work on the coffer plug, when four pumps were sucking out the frigid water. Sometimes "the water sprays out" from between the sheets, and "you come out and change clothes,If so, you may have a cube puzzle ." Thorson said.

"You never know what's going to happen.Unlike traditional high risk merchant account , You want to know where the exits [ladders] are."

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