Big Dig: differenze tra le versioni

Versione delle 18:23, 8 nov 2009

Versione delle 16:21, 22 nov 2009

Riga 32:

Oltre a queste difficoltà politiche e finanziarie, il progetto incontrò molti ostacoli ambientali e ingegneristici. L'area sotterranea del centro, attraverso la quale sarebbe stato scavato il tunnel, era in gran parte già occupata da gallerie della metropolitana e da diverse condutture e tubazioni che avrebbero dovuto essere sostituite o spostate. I lavoratori addetti agli scavi incontrarono diverse e inaspettate barriere geologiche e archeologiche, che andavano dai detriti delle ere glaciali alle fondazioni di case sepolte e ai relitti di diverse navi affondate che si trovavano ora nelle terre strappate alle acque.

Il progetto ricevette l'approvazione degli enti ambientali di stato nel 1991, dopo aver soddisfatto le preoccupazioni circa il rilascio di tossine durante gli scavi e la possibilità di distruggere le tane di milioni di topi, con la conseguenza di lasciarli liberi di vagare per le strade di Boston in cerca di un nuovo riparo. <!-- By the time the federal environmental clearances were delivered in 1994,[18] the process had taken some seven years, during which time inflation greatly increased the project's original cost estimates.[citation needed]

Reworking such a busy corridor without seriously restricting traffic flow required a number of state-of-the-art construction techniques. Because the old elevated highway (which remained in operation throughout the construction process) rested on pylons located throughout the designated dig area, engineers first utilized slurry wall techniques to create 120 ft.-deep concrete walls upon which the highway could rest. These concrete walls also stabilized the sides of the site, preventing cave-ins during the excavation process.

Riga 38:

The multilane interstates also had to pass under South Station's 7 tracks which carried over 40,000 commuters and 400 trains per day. In order to avoid multiple relocations of the train lines while the tunnelling advanced, as had been initially planned, a specially designed jack was constructed in order to support the ground and tracks to allow the excavation to take place below. Ground freezing was also implemented in order to help stabilize the surrounding ground as the tunnel was excavated. This was the largest tunnelling project undertaken beneath railway lines anywhere in the world. The ground freezing enabled safer, more efficient excavation, and also assisted in environmental issues, as less contaminated fill needed to be exported than if a traditional cut and cover method had been applied.[19]

Other challenges included an existing subway tunnel crossing the path of the underground highway. In order to build slurry walls past this tunnel, it was necessary to dig beneath the tunnel and build an underground concrete bridge to support the tunnel's weight. -->

==Note==