le depth and filled with concrete horizontally reinforced, will,
in many instances, give as good results as, and, in most cases, very
much better than, placing the foundation on an equivalent number of
small long piles or a proportionately greater spread of foundation area,
the idea being that the transmission of pressure to the sides of the
coffer-dam will not only confine the side thrust, but will also transfer
the loading in mass to a greater depth where the resistance to lateral
pressure in the ground will be more stable; that is, the greater depth
of foundation is gained without the increased excessive loading, or
necessity for deep excavation.

As to the question of the bearing value and friction on piles, the
writer believes that while the literature on engineering is full of
experimental data relating to friction on caissons, there is little to
show the real value of friction on piles. The assumption generally made
of an assumed bearing value, and the deduction therefrom of a value for
the skin friction is fallacious. Distinction, also, is not made, but
should be clearly drawn between skin friction, pure and simple, on
smooth surfaces, and the friction due to pressure. Too often the bearing
value on irregular surfaces as well as the bearing due to taper in
piles, and lastly the resistance offered by binding, enter into the
determination of so-called skin friction formulas. The essential
condition of sinking a caisson is keeping it plumb; and binding, which
is another way of writing increased bearing value, will oftentimes be
fatal to success.

The writer believes that a series of observations on caissons sunk plumb
under homogeneous conditions of ground and superficial smoothness will
show a proportional increase of skin friction per square foot average
for each increase in the size of caissons, as well as for increase of
depth in the sinking up to certain points, where it may finally become
constant, as will be shown later. The determination of the actual
friction or coefficient of friction between the surfaces of the pile and
the material it encounters, is not difficult to determine. In sand it is
approximately 40% of the pressure for reasonably smooth iron or steel,
and 45% of the pressure for ordinary wood surfaces. If, for instance, a
long shaft be withdrawn vertically from moulding sand, the hole may
remain indefinitely as long as water does not get into it or it does not
dry out. This is due to the tende