The driving of such portions of the river tunnels, with earth top, as
were under the land section, caused a settlement at the surface varying
usually from 3 to 6 in. The three-story brick building at No. 412 East
34th Street required extensive repairs. This building stood over the
section of part earth and part rock excavation where the tunnels broke
out from the Manhattan ledge and where there were a number of runs of
sand into the shield. In fact, the voids made by those runs eventually
worked up to the surface and caused the pavement of the alley between
the buildings to drop 4 or 5 ft. over a considerable area. The tunnels
also passed directly under the ferry bridges and racks of the Long
Island Railroad at East 34th Street. Tunnels _B_ and _D_ were constantly
blowing at the time, and, where progress was slow, caused so much
settlement that one of the racks had to be rebuilt. Tunnel _A_, on the
other hand, where progress was rapid, caused practically no settlement
in the racks.