jack up successfully the roof of a long section of the cast-iron lined
tubes under Joralemon Street in Brooklyn, in connection with the
reconstruction of the Battery tubes at that point, the method of
operation, as partly shown in Fig. 2, Plate XXVIII, being to cut through
a section of the roof, 4 by 10 ft. in area, through which holes were
drilled and through which again the sand was "bled," heavy pressure
being applied from below through the medium of hydraulic jacks. By a
careful manipulation of both these operations, sections of the roof of
the above dimensions were eventually raised the required height of 30
in. and permanently braced there in a single shift.

If water in excess be put into a cylinder containing sand, and pressure
be applied thereto, the water, if allowed to flow out of an orifice,
will carry with it a certain quantity of sand, according to the
velocity, and the observation of this might easily give rise to the
erroneous impression that the sand, as well as the water, was flowing
out under pressure, and, as heretofore stated, has caused many engineers
and contractors to apply the term "quicksand" to any sand flowing
through an orifice with water.

Sand in its natural bed always contains some fine material, and where
this is largely less than the percentage of voids, it has no material
effect on the pressure exerted by the sand with or without water, as
above noted. If, however, this fine material be largely in excess of the
voids, it allows greater initial compression to take place when dry, and
allows to be set up a certain amount of hydraulic action when saturated.
If the base of the material be sand and the fill be so-called quicksand
in excess of the voids, pressure will cause the quicksand to set up
hydraulic action, and the action of the piston will appear to be similar
to that of a piston acting on purely aqueous material.