INNOVATIVE BRIDGE CONSTRUCTION SPEEDS UP MISSOURI HIGHWAY PROJECT
BY SHEILA BACON CAIN
Few construction types are as schedule sensitive as heavy-highway jobs, where even a few hours can mean the difference between a smooth morning commute and complete gridlock. So when Columbia, Mo., general contractor and AGC of Missouri member firm Emery Sapp & Sons (ESS) offered the Missouri Department of Transportation a bridge replacement plan that would close the road to traffic for a fraction of the amount of time proposed by other bidders, the department took notice.
“We liked their option for the sheer fact that it minimized the impact to traffic,” Vicki Woods, MoDOT’s resident engineer and the project’s manager, said. “The time that traffic would be disrupted was cut drastically.”
The scope of the three-month, $13.9 million Interstate 44 project in Missouri’s Laclede and Pulaski counties included the replacement of the steel girders and concrete deck of the 670-ft. bridge over the Gasconade River, part of the westbound lane of I-44. ESS, which was also the low bidder, proposed an innovative “bridge jacking” technique that would ultimately close the bridge lane for only 19 days – less than a third of the 60 days MoDOT had assumed in its RFP. New to MoDOT, the procedure would involve the use of several hydraulic jacks to carefully slide the completed superstructure into place over an 11-hour timeframe.
The project’s success caught the attention of the Alliant Build America judges who honored the job with the “Best Renovation of a Highway and Transportation Project” award in March.
PREPARING FOR THE SLIDE
Work began with the construction of a temporary substructure immediately adjacent to the existing bridge. Here, crews erected new structural steel on these temporary supports, placed and tied rebar, and poured the new bridge’s deck and barrier curb. In the meantime, crews diverted westbound traffic from the existing bridge to the eastbound lanes, creating a temporary head-to-head traffic configuration. The existing superstructure was then demolished. Crews performed modifications to the existing substructure caps before moving the new bridge into place.
“We had to beef up MoDOT’s design, since we didn’t anticipate the slide,” Woods said. The Denver office of engineering firm Parsons was hired by ESS to design the temporary substructure and plan the move of the new superstructure onto the existing columns. “The biggest complication was the interface between the temporary substructure and the permanent substructure,” according to Steve Haines, senior project engineer with Parsons. “The tolerances were very tight to provide a level, smooth transition between the two different components. From a design standpoint, we had to make sure the design elevations matched up with the as built elevations.”
Moving the new 4 million lb. superstructure in place required the expertise of Netherlands-based Houston office of Mammoet, the subcontractor who performed the actual movement of the bridge. Jacks were placed at each of the seven pier locations, then synchronized to push the structure at a uniform rate of speed.
“We didn’t want [the superstructure] to twist or turn out of plane,” Haines said.
The jacks pushed the bridge three feet before retracting and locking back into the substructure. This continued, three feet at a time, for 11 hours. Household dishwashing liquid was used on the piers and sliding bearings as a lubricant during the move. Once the new superstructure was in place, crews tied together the ends of the bridges with the new construction and paved the approaches.
From the time crews diverted traffic to the eastbound lanes of I-44 to the time the new bridge was opened, only 19 days had passed.
AN UNEXPECTED APPROACH
The process of building a new bridge superstructure then sliding it into place is not new technology – it is a form of Accelerated Bridge Construction that seeks to minimize traffic impacts and improve site constructability, and it has become popular in many states throughout the country. It is the first time, however, that MoDOT has used the technology.
Woods and her colleagues were surprised to see ESS’s bid, which differed drastically from the job’s other five bids. MoDOT had expected to use a conventional bridge building process, in which the demolition and construction would be completed in the same spot.
“I was kind of shocked,” declared Woods. “I had to soak it in a little bit.”
MoDOT researched the procedure carefully, and was further comforted by the credentials of Parsons and Mammoet. “We put a lot of time into [the decision] because it was unfamiliar to all of us,” Woods admitted. “But it was worth it. It worked better than we had hoped.”
ESS was experienced in the bridge jacking technique – its crews had performed a similar job for a railroad bridge several years earlier, according to Chip Jones, branch manager for ESS’s heavy civil division. Crews also took the short timeframe into account when proposing the procedure. Bridge work was being performed in the spring, when the river’s levels are known to fluctuate wildly. A more conventional approach would have put crews and equipment in the water for a longer period of time. If rising waters pushed the bridge closure past 60 days, ESS would face hefty fines from the state.
“The way we looked at it, building offsite and moving [the structure] over was less risky than playing down in the river bottom in the spring,” Jones said.
While the contractor’s risk-taking paid off, crews were still faced with a number of challenges throughout the course of the project. After work on the bridge started, two types of endangered mussels were identified downstream. At the time of bidding, there were no restrictions on constructing temporary work pads and crossings in the river channel. Because of this discovery, ESS changed its river access plans from a full stream crossing with pipe culverts to work pads on the banks above the ordinary high water elevation. This also necessitated an increase in crane sizes for structural steel removal and erection operations.
An unexpected 6-ft cavern under the existing substructure discovered while drilling shafts for a temporary bent slowed work, but crews were able to change their methods of operation to overcome it, said Jones. And a record snowstorm in February, when crews were starting work on the temporary substructure, had crews shoveling snow out of the way to keep the job on schedule.
Despite the setbacks, all lanes opened for traffic May 23, 2011.
MORE WORK DOWN THE ROAD
But this is not where the story ends. Often lost in the fanfare of the bridge jacking job’s success is the second half of ESS’s project for MoDOT – the repaving of a portion of westbound I-44, 10 miles away from the bridge replacement.
The two jobs were let by MoDOT as one project even though they were miles apart. “We normally wouldn’t put contracts like this together,” Woods admitted, but the benefits of having one prime contractor as a contact proved to be many. Administration was easier, according to Woods, since things like ramp closures on one job would ultimately affect traffic flow at the other.
Like the bridge job, the paving job was also met with an aggressive schedule proposal by ESS. MoDOT’s maximum closure of the roadway was 45 days. ESS’s proposal offered 37 days, but efficient work and the luck of good weather allowed the job to be completed in just 21 days.
The scope of work included the placement of an 8-in concrete overlay on nine miles of I-44 near Waynesville, Mo. Crews used an optimized mix with a higher concentration of cement, Jones said, which helped the roadway gain strength more quickly. Warm weather also helped the cure rate.
“The combination helped us get strength in about two-and-a half days instead of three-and-a-half days,” Jones said. Performing both jobs under the same contract also helped optimize efforts on ESS’s end as well.
“A lot of the material suppliers and subs were used on both projects,” said Jones.
Attention to detail and the pursuit of an aggressive schedule would prove to be the reasons for the two-part project’s success. With approval of the bid in place, ESS had two months to negotiate and manage engineering design and specialty construction. Once work on both projects started, ESS’s project managers met daily, said Jones, and managed 26 subcontractors and material suppliers, 160 employees (more than half of the company’s workforce) and 80 trucks involving work and material delivery schedules of 24 hours per day, seven days a week.