Jim Bushyeager, Florida Branch Manager for APE, assisted by APE’s California team headed by Steve Cress, have successfully tested questionable drilled shaft foundations in Florida. They used Steve Cress’s Monster pile hammer designed for driving super larger caissons in California for the San Francisco Bay Bridge.
A drilled shaft pier failed causing the bridge to collaspe in April of 2004. It took engineers until December of 2004 to come up with a solution- test them with a big pile hammer. For more details call APE Florida.
Using a 120,000-pound hammer, pounding on highway support columns isn’t exactly a delicate affair.
By JEAN HELLER, Times Staff Writer
Published December 7, 2004
BRANDON – It looks vaguely like a yellow version of the Leaning Tower of Pisa – though not leaning and not quite as heavy. But when it does its thing, there’s no mistaking that something big is going on.
For starters, there’s the massive thunk it makes when a ram weighing 60 tons smacks the top of a pillar of concrete, and the vibration that shutters the ground underfoot as the impact reverberates through soil.
The engineers have dubbed it MOAPH: The Mother Of All Pile Hammers. It is the largest pile driver in the world, and one of a kind. Its home is in California. Its last job was in China.
In a departure from its usual task of driving really big pilings, MOAPH is being used to test 10 to 12 of the support columns under the elevated lanes of the Lee Roy Selmon Crosstown Expressway to determine how secure they are. That became an urgent question after a support column collapsed in April and subsequent problems with soil and column design were discovered.
“This is the sort of test that should make people feel confident when it’s finished that the road is safe to drive on,” said Suzie Boland, president of RFB Communications and spokeswoman for URS Corp., the general engineering contractor on the Crosstown project.
The testing began late Sunday night on column No. 101, the underground support that sits four places to the west of the structure that abruptly sank 11 feet last April.
Preliminary results say the shaft fared well under the pounding, but it was expected to. All the engineers working on the Crosstown project agreed before the test that No. 101 appeared to have adequate underground support.
The 750U Hydraulic Impact Hammer is a 60-ton battering ram in a yellow steel housing. The entire mechanism weighs 150 tons. It took a 200-ton crane to hoist it to the top of the highway support that sits on top of shaft 101.
Once secured, the ram was raised 6 inches and allowed to fall onto the above-ground column. The stress wave created by the blow traveled down both columns and then back up again. By measuring the intensity of the returning wave, engineers will be able to tell what makes up the ground around and under the column.
The stress wave can travel through only solid material. So if the ground around and under the shaft is rock, most of the force of the wave will leave the concrete and continue through the ground. If the subsurface is largely mud, most of the stress wave will return upward.
The test was repeated, raising the ram higher and higher in 6 inches increments, until the stress placed on the column reached 3,100 tons, well in excess of the 2,500 ton maximum load the column was designed to support once the reversible-lane roadway is open and traffic is flowing.
Each time MOAPH was ready to smack the pillar, police stopped traffic in both directions on the Crosstown so the thud of steel on concrete didn’t startle drivers.
“The good news is that the settlement was less than a tenth of an inch after all that,” Boland said. “The engineering standard allows one inch of settlement during construction … and that column basically didn’t move.”
Tom Logan, regional vice president of URS, said a steel saddle and thick slabs of plywood inserted between the ram and the above-ground support column helped dissipate the impact of the blow so it didn’t create small fractures in the concrete. But the protection doesn’t lessen the stress placed on the structure.
“The 10 or 12 of these columns that we’ll test run the gamut of all the different soil components we found along the route (of the 6-mile elevated roadway),” Logan said. “At the end of the day, we’ll know how much rock is at each site, how much clay and how much in between. Then we can extrapolate to all the other columns that exist in similar conditions.”
The testing will take six weeks, largely because moving MOAPH around is a king-sized job.
The cost of the project is $1.5-million.
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Article reprinted with persmission from the St. Petersburg Times.