WHARF CONSTRUCTION, SYDNEY HARBOUR. XLI. 
Sea-walling.—Sea-walling has always proved an obstacle 
in connection with wharf construction, on account of the 
great cost of any kind of masonry or concrete work of 
sufficient weight to withstand the pressure of the earth 
and live load behind it, and in addition the strain of the 
vessels warping in. A concrete or masonry wall of gravity 
section, sufficient to afford a depth of 28 feet at low-water 
costs, even when a good rock foundation is found, at that 
depth, as much as £32 per linear foot of wall. This of 
course renders this style of wall construction practically 
impossible, except in special instances. Where a wharf 
runs parallel to the shore, and at the inshore end of all 
jetties, some kind of sea-wall is necessary. The wharves 
built in the seventies and eighties were usually backed by 
a ballast slope, with several courses of roughly squared 
stones at the top. The toe of the ballast slope standing 
at an angle of repose, 1 perpendicular to 14 horizontal, 
‘usually reached to the front line of the wharf, the depth 
being from 18 to 24 feet. This kind of wharf backing 
served its purpose well enough for many years, but as 
vessels grew in draught of water it became necessary to 
dredge the berths deeper and deeper. This process 
naturally caused the wharf backings to subside, and the 
toe of the ballast slope to extend beyond the front of the 
wharf, where it became a source of danger to the bilges 
of vessels. Many wharves built on this pian are still in 
use, as for instance, the older portion of the Woolloomooloo 
wharves; the wharves from Dawes’ to Miller’s Point, and 
several of the Darling Harbour wharves. 
To cope with the difficulty of the subsidence of the old 
wharf backings, caused by the continual demand for deeper 
water, close sheet piling of turpentine was resorted to in 
many instances. The piles were driven to a sufficient 
depth to secure a hold, and the tops were tied back to 
