A Hitachi backhoe digs near an abutment while other pieces of heavy equipment demolish the existing bridge and load debris into trucks.
Bridge workers and operators of a Self-Propelled Modular Transporter (SPMT), a first time use of this piece of equipment in the state of Minnesota, successfully rolled into place two, 103 ft. (31.4 m) long bridge spans for a bridge crossing I-35E in St. Paul, Minn. By using the SPMT, Minnesota Department of Transportation (MnDOT) staff said construction time was cut by 40 days.
After several hours of turtle-like movement, the SPMT, its operator and team from Mammoet, a Netherlands based company and specialists in this construction technique, moved the pair of decks into place over a short, weekend closure of the St. Paul freeway in the middle of August.
Four weeks later, MnDOT opened the bridge to two lanes of traffic with a full opening of the bridge on pace for late September.
The bridge, carrying four lanes of high volume traffic on Maryland Avenue, an east/west city arterial is the first of seven bridges to be replaced along the freeway over a 5 mi. (8 km) stretch of pavement running north out of downtown St. Paul. It kicks off the first of several contracts totaling more than $100 million to improve traffic capacity, flow and safety through this section of freeway that cuts through the center of St. Paul.
Along with the pavement and bridge improvements, railroad bridges will be replaced, one interchange will be completely reconstructed while road workers will make major road and access improvements to another.
Though trucking, renting, assembling and operating the equipment adds about a million dollars to the project, the down time for the bridge closure is reduced to 60 days or 40 percent in time, MnDOT staff said.
Typically, noted Dave Herzog, MnDOT project manager “a bridge like this would take a little more than 100 days to construct from the time you close it to the time it’s completed. On this bridge, the contractor will do that in 60 days.”
MnDOT awarded the $14 million contract for removing the existing Maryland Avenue Bridge and building its replacement to Lunda Construction, a Black River Falls, Wis., bridge and heavy construction company well known in the Midwest. In turn, Lunda brought in the team from Mammoet to move the bridge decks.
The new bridge is replacing the original built in 1958. The existing bridge has out-dated lane geometrics and is a structure on MnDOT’s priority list for replacement. When completed, regular motorists will cross a much wider bridge with up to date geometrics to make traffic flow more efficiently.
The new bridge features four, 12 ft. (3.7 m) through lanes and a 5 ft (1.5 m) shoulder on each side of the bridge. Additionally, two, 12 ft. left turn lanes will move traffic onto southbound I-35E and one left turn lane will be dedicated to accessing northbound I-35E.
Wider sidewalks on both sides of the bridge will make it safer for both pedestrians and bicyclists to use.
Architecturally, ornamental iron railings, twin lantern style light standards will decorate the bridge deck. Architectural concrete texture limestone and concrete texture cut stone will be placed on the pilasters and abutment portions of the bridge
When Lunda crews mobilized for the project in June, they took over a staging area on the west side of the freeway and about 1,000 ft. (305 m) south of the project site. Here, on temporary piers, bridge crews brought in Terex, American and Grove cranes and a JLG lift, to begin piecing together pre-cast concrete girders for the two decks of the new bridge.
While the deck work continued on the side of the freeway, out of site and more importantly, Herzog said, not interfering with mainline traffic flow, Lunda crews prepared for the demolition of the existing bridge.
With a 60 day deadline to open the new bridge to traffic, MnDOT closed the existing bridge to traffic on the weekend of July 13 to take it down.
With a couple of dozen pieces of heavy equipment including, Cat, Hitachi and Volvo backhoes and dozers, Bobcats and JLG lifts and just a 60 hour window of opportunity, bridge crews, ready for action, moved in around 10 p.m. that night to begin picking away at the old structure.
The following morning brought a steady stream of the curious to the outside edges of the construction site to watch the action and take advantage of some cheap, yet worthwhile entertainment.
Working in very tight quarters, a pair of welders at the surface of the bridge deck cut steel within feet of a nearby Cat backhoe scooping debris into a waiting dump truck. On the opposite side of the bridge, a Hitachi backhoe dug around an abutment.
Below the bridge, a Liebherr backhoe hammered away at fallen pieces of concrete while Cat dozers above and below the bridge pushed debris into piles.
With the bridge gone and the freeway opened on time at dawn of the following Monday, Lunda crews and its sub-contractors began rebuilding the utilities, ramps and new bridge piers and abutments with much of the same equipment used for the demolition.
Toiling under the remaining weeks of a hot, summer sun in July and into some more refreshing and slightly cooler air of early August, both sets of crews stayed on schedule.
As crews at the bridge site closed in on completing the piers and abutments, a steady stream of concrete trucks drove in and out of a service road to the staging area to pump concrete for the pair of bridge decks. While construction activity was quite visible at the bridge site, workers building the bridge decks off to the side of the road were mostly ’out of site and out of mine’ to the thousands of daily motorists speeding by on the nearby freeway.
Halfway through the bridge closure and with the scheduled opening of the new bridge to traffic looming in 30 days, both sets of crews completed their separate parts of the bridge.
Just a thousand feet of pavement and a short, weekend closure would make this bridge complete.
With traffic on I-35E closed off for just the second time of the project in the early morning hours of Aug. 18, the crew of Mammoet specialists and their SPMT moved in to complete the puzzle.
During the early day light hours of that Saturday morning, Mammoet crews moved the SPMT below the first bridge deck and gently lifted it off its temporary piers with a series of hydraulic jacks and a pair of steel beams to bear the load of the deck, weighing approximately 1,300 tons (1,179 t).
And again, the curious came to watch. Though the action was much slower and quiet, the move held their attention.
Moving at the steady and deliberate pace of a turtle, the SPMT and its first load slowly rolled down the empty, silent freeway. With one operator at the controls, he relied on his team of specialists to act as his eyes to guide his mammoth load to its place on the bridge.
Reaching its destination in about an hour and a half, it took another two hours to place the deck onto the bearing pads of the pier and abutment. With only inches to play with over the length of the 103 ft. (31.4 m) long slab of concrete and beams, the operator relied on his team of specialists and 320 wheels at his finger tips to make minute adjustments to the SPMT as he slipped and lowered the deck into place.
“The contractor had a team of people both on the abutments and the piers when the deck was placed onto the bearing pads. They were watching all sides and corners of the bridge to make sure there were no problems. They were checking to make sure there were not any conflicts and that they were making a good closure,” Herzog explained.
The move of the second bridge deck went well, Herzog said and MnDOT opened the freeway to traffic by 10 pm that night.
Besides saving time on construction, the other advantage to relying on a technique like this and one that is not quite as dramatic yet equally important to MnDOT is the decreased impact and frustrations of the traveling public fighting restricted traffic flow, Herzog said.
“With most of the bridge being built on the side of the road, we had very few lane restrictions resulting in considerably reduced effect on traffic on 35E. Really, it’s a huge advantage for the public to not suffer through lane restrictions,” Herzog remarked.
While regular motorists will have their bridge back to them in late September, landscaping and other, miscellaneous work will continue into the fall. Construction will begin on the remaining portions of the overall project next spring with the project to be completed by the end of 2015, according to the MnDOT Web site.
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