FAILURES.
217
forward projection of 7 feet 5| inches in a length of 2,080 feet; an adjoining
wall was thrust forward no less than 13 feet in a length of only 450 feet.
In neither case was the deviation from the vertical of any conséquence,
apparently demonstrating that the slip of the backing extended to a greater
depth than the foundation of the wall.* Immediately upon the occurrence
of the slip, which took place during the process of backing the wall, the
water was admitted to the dock, and no further movement has since
been manifested. The author is personally aware of another case where
the hydrostatic pressure in front of a dock wall constitutes its principal
element of stability. Built, in the first place, with a view to merely
temporary uses, the wall was allowed to remain in conjunction with work
SaaZ» ZOF^ TM.
Fig. 157.—Dock Wall at Southampton.
of a more durable and solid character. An experimental lowering of the
water in the dock, on a recent occasion, had to be abandoned owing to
serious signs of failure showing themselves in the form of cracks and
fissures behind the wall.
Another instance of failure, but of a different kind and somewhat
puzzling as to its origin, is that exhibited in fig. 158, part of which repre-
sents the section of an old wall at the Huskisson Dock, Liverpool. Some
years ago when the wall came to be examined it was found that a portion
of the front masonry, at a depth of 15 feet below the surface level of the
water, had by some means been displaced, had fallen out and was then lying
in the dock bottom. The length affected was about 400 lineal feet, the
disturbance varying from a crack to the maximum gap exhibited in the
* Min. Proc. Inst., C.E., p. 104 et ueq.