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“The tight turns were acceptable when the old
interchange was built more than 40 years ago,” Dehn says. “The sharp
curves on both the old ramps were notorious for catching drivers by
surprise and causing accidents. The new configuration will significantly
reduce dangerous conditions.”
Innovative techniques
Keeping traffic moving while work proceeds is
always a major consideration during road reconstruction. On most
projects, the roadway is not opened until it is completed. However,
sections of the traffic interchange had to be completed in order to move
traffic onto it so the next phase could be built. The construction
traffic control plans indicated that northbound I-19 be reduced to one
lane while the inside lane was completed. When the lane reductions were
put in place, the traffic backup in the area, especially during peak
travel times, reached an unacceptable 2 miles in length. To ease the
congestion, adding extra asphalt to the shoulder created an additional
lane. The work had to be completed after the traffic was in restricted
lanes, but the two lanes, though very narrow, helped to relieve the
backup. Later, when traffic needed to be switched again to complete
northbound I-19, the extra lane was built prior to the switch, providing
two lanes right from the start.
Another construction problem was the
installation of a drainage pipe beneath I-10. Ordinarily, this would
have involved an additional traffic switch and a jack-and-bore operation
on a 66-inch section of pipe. An alternate method of placing the
drainage pipe under and across the interstate was developed. The
drainage pipe was installed as far as possible without interrupting
interstate traffic, and the detour was built over the completed section
of pipe. Next, the detour was swung a bit wider than had been planned
and a little more pavement was added to it. That created enough room to
keep interstate traffic moving while the open trench construction
continued.
The demolition of nine bridges would ordinarily
be a time-consuming, troublesome process conducted in two separate
stages. First, the concrete would be crushed, then crews would arrive to
cut and remove the remaining rebar. However, an innovative technique
was employed, using a state-of-the-art piece of equipment called the
DemoPro. The DemoPro grabbed and crushed a section of concrete with its
scissor-like jaws and continued to clamp down and cut all the way
through the rebar. This method cut a full week from the demolition time
of each bridge, a total saving of more than two months on the project
schedule.
Environmental considerations
Extensive archeological evaluation during the
design phase of the project led to a surprising discovery. Excavation
unearthed a prehistoric settlement that had been occupied for more than
1,500 years. From approximately 400 B.C.E. to 1150 C.E., a section known
as the Julian Wash area was part of a series of large Hohokam and pre-Hohokam
villages that bordered the Santa Cruz River. Nearly 100 prehistoric pit
houses and household articles were exposed, along with a portion of an
orphanage, St. Joseph’s Children’s Home. These areas were fenced off and
left undisturbed during the construction process.
Another environmental measure involved the
development of a Stormwater Pollution Prevention Plan, which addressed
the problems of soil erosion, the loss of topsoil, and possible
contamination of soil during construction activities.
“The Crossing is one of the largest highway
improvement projects undertaken in southern Arizona during the past
decade, in both size and importance,” says Olivares. “It was completed
on time and under budget, and it has improved traffic flow and safety in
one of the busiest traffic intersections in the state.” |
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