Big Lessons from the Big Dig
One-hundred and sixty-one lane miles of highway. More than three
million cubic yards of concrete. Five miles of steel-reinforced concrete
slurry tunnel walls. And that's just for starters. The Central Artery/Tunnel
Project in Boston, Massachusetts, better known as the Big Dig, is
one of the Nation's largest and most complex highway projects. The
14-year endeavor, scheduled for completion in 2004, will replace an
existing 6-lane elevated viaduct structure with a 10-lane underground
expressway. During the course of construction, the project has produced
a number of firsts, from the largest application of slurry walls to
the widest cable-stayed bridge in the world to the most extensive
highway tunnel ventilation system ever constructed. A number of these
technological advancements are now being highlighted in the Federal
Highway Administration's (FHWA) Innovations and Advancements Program,
which consists of a series of instructional presentations that can
be scheduled by highway agencies.
"There's a lot that has been learned from this project, and everyone
can benefit from it," says Daniel C. Wood of FHWA. The presentation
modules focusing on technology innovations include Urban Applications
of Slurry Wall Technology, Soils Improvement Techniques, Intelligent
Transportation System (ITS)/Traffic Simulation Model, and Tunnel Fireproofing
and Ventilation Systems.
The Slurry Wall Module describes this technique for tunnel wall construction
and stabilization, which allows excavation work to be performed in
a confined space while still maintaining continuous traffic movement
above. The Soil Improvement Techniques module looks at methods used
to stabilize soil. One such method is soil freezing, which enabled
engineers to construct a tunnel big enough for an Interstate without
disrupting the nine active railroad tracks traveling just above the
tunnel space.
Instead of digging a tunnel, hydraulic jacks were used to push tunnel
boxes up to 380 feet long under the railroad tracks. Due to soft soil
conditions under the tracks, ground freezing was necessary to stabilize
the soil before performing the tunnel jacking, so that the tracks
would not settle and endanger rail operations. This was accomplished
by pumping a brine mixture through hundreds of pipes installed between
the tracks. Over the course of several weeks, the circulating brine
drew the heat from the soil and froze the ground outward from the
pipes.
The tunnel fireproofing and ventilation system module details the
project's use of the largest mechanical ventilation system in the
world. It also covers how the project conducted a full-scale tunnel
fire test program to improve tunnel safety. The Big Dig's Integrated
Project Control System, meanwhile, is described in the ITS/Traffic
Simulation Model workshop. The system will use more than 35,000 data
collection points to manage traffic and incidents, as well as such
things as ventilation, lighting, security, and air quality. It will
also collect data on traffic speed, volume, and congestion and distribute
information to motorists through such means as electronic message
boards and lane control signs.
One State that has already hosted a workshop is Connecticut. "After
seeing the presentation on tunnel jacking, they changed one of their
projects to use the tunnel jacking technique," says Wood.
For more information on scheduling a workshop, contact Wood at 617-494-2462
(email: daniel.c.wood@fhwa.dot.gov).
Information on the Big Dig's use of innovative technologies can also
be found on the Web at http://bigdig.com.
Other
articles in this issue:
In Brief
New Standard Has States Speaking the
Same Language on Pavement Cracking
Big
Lessons from the Big Dig
States Achieve Safety and Savings with
Rapid Deployment for Bridge Planning
Introducing the New and Improved Hot
Mix Asphalt Paving Handbook 2000
A Plan for LTPP Products
Highway technology calendar
