Fig. 28. The piles are of greenheart, and were driven to a
solid foundation. The 1 3/4 in sheeting was driven to support
the sides of the excavation, and was left in when the concrete
was laid. Light steel rails were laid under the sewer, in
continuous lengths, on steel sleepers and to 2 ft gauge. The
invert blocks were of concrete, and the pipes were made of the
same material, but were reinforced with steel ribs. The Waterloo
(near Liverpool) sea outfall is shown in Fig. 31.

[Footnote 1: Plate V.]

Piling may be necessary either to support the pipes or to keep
them secure in their proper position, but where there is a
substratum of rock the pipes may be anchored, as shown in Figs.
25 and 26. The nature of the piling to be adopted will vary
according to the character of the beach. Figs. 27, 29, 30, and
31 show various types. With steel piling and bearers, as shown
in Fig. 29, it is generally difficult to drive the piles with
such accuracy that the bearers may be easily bolted up through
the holes provided in the piles, and, if the holes are not
drilled in the piles until after they are driven to their final
position, considerable time is occupied, and perhaps a tide
lost in the attempt to drill them below water. There is also
the difficulty of tightening up the bolts when the sewer is
partly below the surface of the shore, as shown. In both the
types shown in Figs. 29 and 30 it is essential that the piles
and the bearers should abut closely against the pipes;
otherwise the shock of the waves will cause the pipes to move
and hammer against the framing, and thus lead to failure of the
structure.