Engineering
Boston, Massachusetts one of the oldest cities, is a busy community with high percentage of roads chocked with traffic. In order to relieve the traffic issues and to provide the residents with more parks and recreational facilities instead of roads, an ambitious project was undertaken known as the Central Artery/Tunnel Project (CA/T). The project basically encompassed on the vision of building an underground tunnel, miles below the surface, without disturbing the daily routine and holding up traffic for construction. In order to achieve this daunting task many changes had to be undertaken, which could ire the everyday commuter. The following paper discusses at length the problems as well as the solutions undertaken to successfully complete the project.
States and Cities across America consist of mega infrastructures which help to interconnect various places internally. But to maintain such extensive infrastructure, USA has to spend millions of Dollars for its maintenance. In Boston, Massachusetts, an ambitious project was undertaken but The entire project was plagued with various problems and issues overcoming which seemed impossible.
The first and the foremost problem were to redirect two hundred thousand every day commuters from their usual roads to the maze of tunnels and highways. Engineers feared that commuters would not be able to comprehend the changes made by the new lane and thus result in accidents, as commuters might swerve into the lanes at the last minute in order to reach their desired destination. Replacing the old Central artery, with a tunnel was extremely difficult,in no ways could the traffic be stopped, thus the major task was do the construction while the central artery was functional, without disrupting the traffic. Fred Salvucci, former secretary of Transport was the pioneer in developing this vision of building the tunnel underground while yet supporting the artery, thus letting the traffic flow. Salvucci was also concerned with the displacement of families in order to build the ambitious project; he thus reassured residents that the families would not be affected while the construction was ongoing.
In 1991 the actual construction of the Big Dig began and in 1992 the first tunnel section arrived in Boston. Over the next year 11 more such tunnel sections arrived to build a route to give commuters the chance to escape the traffic of downtown and instead travel through another route to the airport. When the marine tunnels were built, the concern wsa to place the tunnels at a fraction of an inch to the land based tunnel in order to ensure proper adjoining and a water tight seal. This proved to be difficult given the murky water, which made it difficult for the divers to see underneath. To achieve this, GPS, satellite information and laser shots were taken to insure proper positioning. Being 100 feet below the surface, this was supposed to be the deepest tunnel connection ever made. But successful completion resulted in the opening of the tunnel in December, 1995.
After the completion of the Ted Williams Tunnel, the challenge was to connect it with the inter-state 90. To achieve this a ten-lane highway needed to built that crossed a subway, post office and the largest factory, and below the rail line. To add to the challenges, the soil in this area was the weakest, thus making it difficult to build the project. Answer to this problem was found in the constructions in Japan, where the soil is extremely unfavorable for construction, they mixed the existing soil with cement thus making it possible for construction. This took 3 years in order to make the soil strong enough for construction. While this problem was being solved, another problem loomed, the channels low bridges prevented the tunnel sections from being built offsite. To overcome this problem, basins were built where the tunnels were constructed and then the basin was flooded in order to guide the tunnel towards its designated area. Long basin with dam long enough to hold back the water was constructed and thus the building of tunnel sections began. Another concern for the engineers was the safety risk of placing the 100 thousand ton tunnel at the Red Line, thus water locking doors were placed in the Red Line to avoid flooding in case of any mishap.
While connecting the tunnel with the Interstate-90, it had to pass through below the rail tracks, without disrupting it. The issue here again was of loose and weak soil. The solution was to freeze the soil underneath, which was achieved by installing 2000 pipes around the tracks with water chilled up to -30° thus creating a large manmade iceberg which made the soil hard enough to work on it. The large tunnel sections were pushed using tunnel jacking, while protecting the upper rail tracks. Steel sections were placed above in order to support the rail tracks. While things seemed in place, water started seeping through the land and water tunnel adjoining at the 4th point Channel due to which the tunnel was flooded with water, due to this the schedule was pushed back costing several million dollars loss.
Engineers building below the interstate-93 were faced with other challenges especially relocating of the 300 old infrastructure of pipes, wires etc below the surface. Apart from the pipes and the human traffic was the problem was to keep the Red Line and the underground bus service intact, yet build the Big Dig underneath them.
Connecting the Tunnels underneath to the highways above was another daunting task, as the existing bridges had to be kept untouched, for the regular passage of traffic, thus bridge around it had to be built. Therefore a large asymmetrical bridge that could carry 10-lane traffic of the Interstate-93 was built. Another concern was the normal accidents within the tunnel that might cause fire. To fight this problem, 7 ventilation building were built as well as intelligent computer systems were designed to overcome the fire issues.
In 2003, a series of opening of the I-90 and I-93 was carried out and thus the Big Dig was completed and the most ambitious project was opened to public, after overcoming every issues and obstacles. Although the cost was much more than expected, it has proved to be fruitful.
References:
http://www.youtube.com/watch?v=j4fi7DCD4Bs
