|
A Long and Winding Road
Tampa's Reversible-Lanes Bridge
Finally Nearing Role as Mass-Transit Solution
By Bill Chastain
Finally overcoming a major engineering failure that led to
structural collapse and plenty of fallout, construction of
an elevated, reversible-lanes portion of the Tampa-Hillsborough
County Expressway Authority's Lee Roy Selmon Crosstown Expressway
is back on track.
That's a major development, considering the series of setbacks
that have delayed the finish of the reversible roadway.
The project's initial cost was $372 million, and it was supposed
to be completed last July. But movement by several piers -
including one that sank 11 ft. in a virtual collapse - caused
severe damage to the structure and threw into question the
safety of the entire roadway. Overcoming that safety concern
would require an intensive investigation and, ultimately,
repair work that would add more than one year to the schedule
and about $100 million to its budget.
Since the troubles, the authority's executive director, Patrick
McCue, has been fired, the authority has sued its engineer,
San Francisco-based URS Corp., for at least $120 million and
extensive repair work has been performed. According to the
authority, the project now has a total cost of approximately
$470 million and should be up and running by August.
Model for Mass Transit
The project was conceived as a showpiece structure and a model
solution for addressing a certain chunk of Tampa's traffic-congestion
problems.
Heavy commuter traffic between Brandon and downtown Tampa made
the innovative reversible-lanes elevated toll road an attractive
solution when the authority approved the plan to build it in
1999. The roadway would facilitate one-way traffic heading downtown
in the mornings and then it would be reversed to accommodate
the evening commute back to the suburbs.
What made the design look even more sensible was the project's
lack of intrusiveness. The plan called for a three-lane, concrete
elevated portion to be built on piers within the median of the
Lee Roy Selmon Crosstown Expressway. Moreover, no rights-of-way
had to be obtained and the piers used just 6 ft. of the expressway's
40-ft. median.
At the time, Linda Figg, president of Figg Engineering, the
Tallahassee, Fla.-based designer of the bridge's superstructure,
even called it "the answer for the future of urban transportation."
In addition to the project having reversible lanes that will
be routed according to the time of day to ease the burden of
the heavy traffic flow, there are gateways at each end to prevent
a traffic build-up at the end of the commute.
"We didn't just dump traffic into existing systems,"
said Ralph Mervine, executive director of the Tampa-Hillsborough
County Expressway Authority. "We opened up new gateways
in Tampa at Meridian Street, and we opened up a new gateway
into Brandon, which is Brandon Boulevard. We're certainly opening
new gateways on both ends with the anticipation that it will
not bottleneck."
The 60-ft.-wide bridge structure was designed to facilitate
three 12-ft. traffic lanes and two 10-ft. shoulders. The bridge
would be made up of approximately 196 142-ft. spans made up
of 3,032 90-ton segmental units that PCL Civil Constructors
of Tampa precast near the Port of Tampa.
From there they could be easily delivered to the site by 14-axle
trucks hauling 140-ft.-long trailers. The construction team
would then use a 250-ton crane to place each segment onto a
custom-fabricated truss used for final erection.
PCL had the $145 million contract to construct most of the elevated
6-mi. portion leading to the downtown area as well as a section
passing over Interstate 75. PCL's contract included three bridges
of 4,000 ft., 7,000 ft. and 17,000 ft.
History: Great Start, but . . .
The project got off to a grand start on Jan. 12, 2003.
PCL began by drilling shafts to 70-ft. depths and pouring some
of the supporting piers while eventually erecting at a rate
of approximately 64 precast segments per week. The contractor
had manufactured approximately 50 percent of the project's 3,302
total segments by late March 2004.
Given the pace established, the forecast that the project could
be finished six months ahead of the July 15, 2005, completion
date seemed reasonable.
But the project suffered the first of several major blows on
April 13, 2004, when pier No. 97 sank 11 ft. into the ground,
resulting in two 150-ft. sections of roadway buckling. Inspectors
then discovered on July 6, 2004, that pier No. 99 had settled
1.3 in. Acceptable design margins allow bridge piers to sink
no more than 1 in. during construction. Pier No. 97 sat 240
ft. east of No. 99.
The authority hired Ardaman & Associates, an Orlando-based
engineering firm, to oversee testing of the existing piers and
the locales of future piers for the project. Additionally, Florida
Department of Transportation engineers took a second look at
Ardaman's calculations that essentially cited fundamental design
flaws in foundations.
According to FDOT officials, URS engineers overestimated the
strength of the limestone layer supporting the piers and decided
it was safe to build shallower foundations. Foundation sites
were tested by core borings that yielded a cross-section for
examination. The borings extended past the lowest point where
the foundations were to reach but did not go deep enough to
uncover problems.
A lawsuit between URS and the authority is pending.
Repair
Meanwhile, a foundation repair program began and the project
proceeded from there. HNTB of Lake Mary, Fla., was hired to
fulfill remaining engineering duties through project completion.
HNTB is responsible for the completion and oversight of the
project and will also provide engineering and construction services
for anything the authority constructs, operates and maintains
for the metropolitan highway system.
The final count identified 155 of the 224 piers that had to
be repaired. Repairs were broken down into two different categories:
those strengthened by sister shafts and those strengthened by
minipiles.
"It was felt that that was the safe way to proceed,"
said Mervine, a former FDOT employee who was hired after the
agency terminated McCue. "We have communicated this extensively
to the public and other leaders and it's our impression everybody
believes we're doing the right thing here for us to have a safe
structure."
Figuring out which damaged piers needed sister shafts and which
needed minipiles came down to figuring basic loads with an added
safety factor.
"If we felt as though the original 6 ft. drilled shaft
was deficient in its ability to carry basic load when the bridge
was constructed on top of it, we would make that repair with
sister shafts," Mervine said. "If we felt as though
the original 6-ft. shaft was deficient only in safety factor,
then we would make up that difference in minipiles."
The sister shaft remedy was prescribed for 68 of the 155 piers
to be repaired. The job called for 4-ft.-diameter shafts to
be placed on either side of the existing pier and drilled down
below the original one.
"There were extensive soil borings that were taken and
then they drilled them down anywhere from 15 to 20 ft. below
the shafts," Mervine said. "From that standpoint [all
of the sister shafts] were similar.
"In the case of pier No. 97, the one that failed, those
were two 6-ft.-diameter shafts. That one was different because
the shaft was gone. It sunk 11 ft. so it was useless."
In cases where the bridge had already been built, shoring towers
were placed under the bridge and used to jack up the existing
structure about an inch to take it off the original shaft and
allow the sister shafts to be installed. Then a footer was built
around the finished product before reloading the whole system
together.
"The purpose of these was to strengthen the soil,"
Mervine said. "That was a different concept than the sister
shaft. The sister shaft actually took load whereas the mini-piles
were strengthening the soil and keeping the shaft from twisting."
They went alongside like the sister shafts, but helped in a
different way.
The minipiles "go down around the original shaft and help
it so when that shaft wants to twist or turn, they're down there
to help strengthen that soil," Mervine said.
Approximately 87 piers were earmarked for the minipile solution,
which meant over 500 minipiles will be used on the project repair.
"The original expectation was that each minipile would
be able to take a load of 100 tons," Mervine said. "After
a couple of them were in place and tested, we found they could
take 130 tons."
The task of executing the repairs fell to PCL.
"It was a tremendous amount of work that had to be coordinated
and planned carefully, and a lot of resources had to be put
into place so the thing could be done in a sequence that allowed
the subsequent operations to take place the way we planned to
do them," said Jerry Harder, PCL district vice president.
He added that of the 155 damaged piers, approximately seven
still need repairs and there remain approximately 20 spans of
the total 200 to be completed.
"PCL has done a good job in project recovery," Mervine
said. "Let's make sure we're clear on this. It was an engineering
error, not a construction error. And PCL has done a good job
in recovering the project and getting the foundations repaired
as well as getting the bridge construction re-started. And we're
looking forward to opening the project by the end of August."
Mervine remains convinced the reversible-lanes section of the
Lee Roy Selmon Crosstown Expressway will remain as a prototype
for other areas to examine when considering solutions to their
traffic problems.
"We've had a lot of interest from other cities to see how
the concept works," he said. "Most everyone is looking
beyond the design problem we had and they're more interested
in the functionality of it now." |
print this page
e-mail this page
