NON-STOP TO BOSTON

In order to prevent disruption of train service at Boston's South Station, which handles approximately 400 trains daily, tunnel jacking has been used as part of the Central Artery/Tunnel project to place three sections into the deepest part of the project. The entire concept of sliding a tunnel underground using a huge pit and powerful jacks was relatively new to the United States. Alternatives, however, were scarce. Boston's pasty historic soil created a mess of problems throughout the tunnel line, and the complexities magnified when the design team was dealing with tunnel jacking forces in need of a solid foundation. Jet grouting was used to counteract the soft soil and improve base stability during the construction of the jacking pits, which are roughly 100 ft wide and 200 ft long. Ground freezing was another technique used to combat the weak clay and organic layers during tunneling. Upon completion of the tunnels, a portion of the pit headwall was demolished and the process of pushing the sections underground began.