HISTORY OP CIVIL ENGINEERING IN NEW SOUTH WALES, 637 



This work was completed some years ago, and was successful in 

 every respect. It is covered by a large embankment, made of spoil 

 from the outfall sewer works, on which a roadway has been formed. 

 The sewage can also be diverted into this overflow sewer should it 

 ever be found necessary to do so. Provision is also made at two 

 other points on the sewer for storm-water relief and diversion of 

 sewage when local conditions were favourable ; but as the admission 

 of storm-water is carefully regulated, the overflow at Deep Dene 

 will probably meet all possible requirements in this direction. The 

 greatest quantity of rainfall admitted on any portion of the area 

 drained by this system is at the rate of half an inch in twenty- 

 four hours, and any rainfall in excess of this provision will find 

 its way to the harbour by the old sewers, or by street gutters or 

 natural watercourses. The northern system comprises the follow- 

 ing new bi'ick and concrete sewers : — Outfall sewer, five miles, 

 two thousand seven hundred feet ; Prince Alfred Hospital inter- 

 cepting sewer, one mile fourteen hundred feet ; Pyrmout branch, 

 one mile two thousand one hundred feet ; Kent-street intercepting 

 sewer, one mile three thousand nine hundred feet ; Bridge-street 

 and Harrington -street intercepting sewer, one mile four thousand 

 seven hundred feet ; Riley-street and Bourke-street intercepting 

 sewei', two thousand feet ; Lacrozea Cteek branch, fifteen hundred 

 feet ; Rushcutter's Bay overflow sewer, two thousand five hundred 

 feet ; proposed extensions to Glebe, Balmain, &c. (shown in dotted 

 lines on sketch plan), five miles two thousand feet — total, eighteen 

 miles six hundred and eighty feet. Some stoneware pipe sewers 

 have also been laid up to twenty -four inches diameter, and a large 

 amount of work remains to be done in laying pipe sewers or 

 sub-mains. Concrete has been largely used in the construction of 

 the sewers, as will be seen from cross sections of sewers on Plate 

 XL., and all bricks used in the work are of very high quality 

 The concrete (except that used for packing purposes) is composed 

 of blue-stone, broken to a one and a-half inch guage, sand and 

 Portland cement in the following proportions : — Four parts of 

 stone, two parts of sand, and one part of cement. The bricks 

 were nearly all supplied from two brickyards, and average 

 samples taken from them were tested at the Sydney University 

 Engineering Laboratory, with the following results : — Average 

 crushing resistance per square inch, two thousand seven 

 hundred and eighty-two pounds and two thousand two hundred 

 and twenty-eight pounds. The crushing resistance of English 

 Stourbridge fire-bricks is about one thousand seven hundred and 

 seventeen pounds per square inch, and of London red brick about 

 eight hundred and eight pounds per square inch. The tunnels are 

 lined throughout, the minimum thickness of lining adopted being 

 four and a half inclips. In rock tunnels the lower part of 

 the sewer up to a height of twelve inches above the springing 

 level is lined with bluestone concrete, and the arch is closed with 



