214
DOCK ENGINEERING.
Fig. 154. —Quay at Altona.
As has already been
pointed out, the most
treacherous of all strata,
from the point of founda-
tion for a quay wall, is
the blue clay. Out of
many instances, which
might be cited as évi-
dence of its dangerous
nature, the following ac-
count of the sliding for-
ward of a wall at the
port of Altona is selected
as affording an interesting
example of remedial nrea-
sures adopted with perfect
success : —*
The town of Altona is
situated on the right bank
of the River Elbe, and the
level of the ground rises
gradually from the river
bank inland to a height
of 105 feet. The town
stands partly upon this
slope and partly upon its
summit.
The uppermost stratum
of the site (fig. 154) con-
sists of very fine sand,
interspersed with numer-
ous water streaks. Below
this sand is a layer of
clay, which rises to the
hills at an angle rather
less than the surface in-
clination. The clay is
firm when not saturated
with moisture. It is, how-
ever, soluble in water,
and becomes a smooth,
soapy body, offering no-
effective resistance to slid-
* Min. Proc. Am. Soc. C.E.*
vol. XXX.