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Given the circumstances of the roadway and the
surrounding area, CDOT realized many issues needed to be resolved. Under
normal replacement procedures, detours would have to be constructed adjacent
to each bridge. The construction of the detours would have displaced about
200 trees and encroached upon wetland areas. Pipes would also need to be
installed for river flows, thereby adding silt to the river.
In addition, one of the sites would accommodate a
detour for one-way traffic only, which would have required the installation
of temporary traffic signals to regulate the traffic. The traffic signals
would create delays for the traveling public as it would take at least five
minutes for one direction of traffic to get through the construction zone
and get the other direction moving. This detour would have been in place for
several months, impacting the tourists as well as the many commuters in the
area.
“After reviewing the original replacement procedures,
we realized that the situation was not ideal,” said CDOT Project Engineer
Michael Command. “The environment was going to be greatly impacted and the
traveling public would experience delays for many months. Knowing that the
actual bridge replacement would take place in the summer, it was necessary
to find an alternate plan.”
Quick replacement
With these concerns in mind, CDOT and Lawrence
Construction worked together to devise a new plan. In the end, CDOT decided
that the bridges would be replaced over a 10-day period, in which U.S. 34
would be completely closed for about 2 miles. Under this new procedure, a
large portion of each bridge would be constructed off-site prior to the
closure. Once the closure began, crews would deliver and place the sections
of the bridges; thus, allowing for a quick bridge replacement procedure.
Once a plan was laid out, it was time to share the
information with the traveling public. CDOT delivered flyers, mailed out
letters, and met with the businesses and schools in the community in order
to inform the public of the new construction plan. In addition, CDOT had to
work with Larimer County officials to obtain permission to use the county
roads for the planned detour route.
“One of the most challenging aspects of this project
was getting the public to understand why a quick 10-day closure would be
more beneficial than months of construction,” added Command. “After
explaining the circumstances of the project, the community was on our side
and ready for the closure to commence.”
How they did it
Under the new procedures, the project would begin in
the spring of 2004 with the ground work while sections of the new bridges
were constructed off-site. The preparatory work consisted of the
construction of the caissons, columns, and abutments. This work took place
through mid-June under minimal daytime lane closures. By mid-June, the
majority of the preparatory work was complete and it was almost time for the
bridge replacement to begin, but there was one problem. The tourist season
was heading into full swing, which would mean greater impacts to the
traveling public. As a result, CDOT elected to suspend the bridge
replacement until mid-September when traffic was lighter.
After months of preparation, CDOT closed U.S. 34 and
began the bridge replacement. With 40 workers prepared to take on the
challenging task, the replacement got off to a great start. Within 24 hours,
both bridges were removed.
Over the next few days, 16 girders were placed on one
of the structures and placement got underway on the second structure. The
placement of the girders on the second structure is where crews ran into
some problems — the girders were not sitting squarely on the abutments.
However, the problem did not hinder the process. Within a few hours,
engineers determined it was necessary to shim the piers in order to level
out the girders and the next step of the project was underway.
As work continued, it was apparent to the crews that
the girders would not be their only problem. Towards the end of the fifth
day, Mother Nature brought rain to the project, which softened the subgrade
soil. Due to the time crunch, efforts were taken to haul in competent
subgrade material so that paving could take place as quickly as possible.
The softened soil, along with the girder issue, would delay the efforts, and
the 10-day closure soon became a 14-day closure.
“CDOT was concerned with the delays brought on by the
girders and soft soil which extended the closure,” said CDOT Resident
Engineer Scott Ellis. “However, we decided that a quality project would more
than make up for a few more days of inconvenience.”
Just when the crews thought the end was near, they
encountered one last problem. It was discovered that a rock fissure was
allowing water to leak into the roadway subgrade near the upper bridge. Once
again, CDOT engineers and the contractor put their heads together and
designed a drain system to divert the water elsewhere.
Just five days after the decks were poured, U.S. 34
reopened to traffic with two new concrete box girder bridges that are safer
for the traveling public. The upper bridge is now 149-feet long and 43-feet
wide as opposed to 130-feet long and 35-feet wide. The lower bridge is
219-feet long and 43-feet wide, which is 54-feet longer and 8-feet wider
than the old bridge. The extra width gives motorists and bicyclists more
room and makes it easier for the two to share the road. Also, the new
roadway alignment around the bridges enhances the site distance, making for
a safer roadway.
Even though the bridges were completed in November
2004, the top mat of asphalt could not be placed because of the cold
temperatures. Once the temperature warmed up, crews had to return to place
the top mat of asphalt on both bridge decks. The paving was also conducted
under minimal lane closures and was completed by April 2005.
The costs
The $2.6-million project that was scheduled to take a
year and half to complete was actually completed several months ahead of
schedule and with significantly less delays than originally expected.
“This project is a great example of how CDOT and its
contractors work together to accomplish great things,” added Ellis.
“Everyone on this project team worked together to overcome a difficult
situation and in the long run, the traveling public and the environment
benefited greatly. The hard work and innovation demonstrated in this project
raises the bar for future transportation projects in Colorado.” |
