writer has made some
experiments which appear to be conclusive, showing that, except in pure
quicksand or wholly aqueous material, as described later, the earth and
water pressures act independently of each other.

For a better understanding of the scope and purpose of this paper, the
writer divides supersaturated or subaqueous materials into three
classes:

_Class A._--Firm materials, such as coarse and fine gravels, gravel and
sands mixed, coarse sands, and fine sands in which there is not a large
proportion of fine material, such as loam, clay, or pure quicksand.

_Class B._--Semi-aqueous materials, such as fine sands in which there is
a large proportion of clay, etc., pure clays, silts, peats, etc.

_Class C._--Aqueous materials, such as pure quicksands, in which the
solid matter is so finely divided that it is amorphous and virtually
held in suspension, oils, quicksilver, etc.

Here it may be stated that the term, "quicksand," is so illusive that a
true definition of it is badly needed. Many engineers call quicksand any
sand which flows under the influence of water in motion. The writer
believes the term should be applied only to material so "soupy" that its
properties are practically the same as water under static conditions, it
being understood that any material may be unstable under the influence
of water at sufficiently high velocities, and that it is with a static
condition, or one approximately so, that this paper deals.

A clear understanding of the firm materials noted in Class A will lead
to a better solution of problems dealing with those under Class B, as it
is to this Class A that the experiments largely relate.

The experiments noted below were made with varying material, though the
principal type used was a fine sand, under the conditions in which it is
ordinarily found in excavations, with less than 40% voids and less than
10% of very fine material.

[Illustration: FIG. 7.]

_Experiment No. 2._--The first of these experiments, which in this
series will be called No. 2, was simple, and was made in order to show
that this material does not flow readily under ordinary conditions, when
not coupled with the discharge of water under high velocity. A bucket 12
in. in diameter, containing another bucket 9 in. in diameter, was used.
A 6 by 6-in. hole was cut in the bottom of the inner bucket. About 3 in.
of sand was first placed in the bottom of the larger bucket and it was
partly filled with water.