Hoosac Tunnel, Western Portal – North Adams, MA

Hoosac Tunnel, Western Portal – North Adams, MA

Geotechnical Problem:   Outside the Western Portal, an exposed rock face on the southern side of the tracks, contained a schist deposit, known by the old timers as “demoralized rock”.   This schist had made tunneling the Western Portal quite difficult in the 1850’s.   The rock was effectively deteriorating into a silt through exposure to water.  This newly formed silt was heavily migrating to the tracks and covering the ballasts.   In fact, so much of this silt was migrating, large void spaces, effectively caverns, were left behind within the exposed rock walls lining the tracks.  Water was now flowing through those caverns and carrying more silt to the tracks.

In addition, an access road was located on the top side of this schist deposit.    A major surface depression developed in the roadway from the silt migration below.   The access road could not be restored until the void spaces below were filled in.

Polymer Grouting Solution:   EFT filled the void spaces, adjacent to the active railway, with an expanding polymer grout.    This material rapidly expanded and filled the in void spaces.   The polymer grout effectively cut off the primary pathway for silt migration minutes after injection.

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