The question of tunnels under the North River was an uncertain factor in
the larger Pennsylvania Railroad scheme, owing to the nature of the
ground composing the river bed in which the tunnels would be
constructed.

It is well known that about 35 years ago an attempt was made to
construct a tunnel under the North River by using a "Pilot" system under
compressed air and forming the tunnels in brick masonry. Owing to the
very soft nature of the materials through which it passed, several
serious accidents occurred, and the work was abandoned after about 2,000
ft. of tunnel had been constructed. Later, this work was taken up again,
when a shield was installed and an additional 1,800 ft. was built with
cast-iron segmental lining, but the work was again abandoned, owing
principally to financial difficulties while coincidentally before
entering a rock reef which presented another serious difficulty in
construction. The experience then in the construction of this tunnel led
capitalists and engineers to believe that, owing to the very soft nature
of the ground, a tunnel could not be built that would be sufficiently
stable to withstand the vibration due to heavy traffic, and for this
reason tunnels under the North River were not looked upon as
practicable. The writer devised a scheme to carry within the tunnel the
rolling loads on bridging supported on piers or piles extending from
the tunnel invert down to hard material. These would be attached to the
tunnel itself or would pass into it independently through sliding joints
in the tunnel shell. This scheme gained the confidence of the
management, as it was believed that, by adopting such a plan, tunnels
could be built in the soft material underlying the Hudson River and
remain stable under all conditions of traffic. After thus feeling
assured that by this method the tunnels could be made safe beyond