HISTORY OF CIVIL ENGINEERING IN NEW SOUTH WALES. 039 



was attributed partly to the hardness of the rock, but principally 

 to the occurrence in the rock of ironstone bands and nodules. In 

 more favourable ground it is believed the machine would have 

 been successful. 



Mr. Bennett, in the prosecution of his inquiries as to tunnel- 

 boring machines for small tunnels in the city, obtained, as far 

 back as 1881, drawings and particulars of Doering's machine, but 

 the rate of progress with them would have been so slow, or the 

 number of machines required so great, that their adoption was 

 not considered feasible. 



The portions of the work which present most interest from an 

 engineei'ing point of view are on the outlet end of the outfall 

 sewer. (See PI. XL.) A length of one mile three thousand 

 three hundred feet, connuencing at the ocean outlet, was let in one 

 contract. For one mile of this length the sewer is eight feet six 

 inches by seven feet six inches, and for the remainder of the 

 length it is eight feet two inches by seven feet two inches. It is 

 constructed in tunnel on sandstone rock for three thousand nine 

 hundre'l and sixty feet of this length, in tunnel in water-charged 

 sand for one thousand six hundred and forty-three feet, and in 

 open cutting in water-charged sand for two thousand nine hundred 

 and seventy-seven feet, as shown on the longitudinal section. The 

 construction of the sewer through the water-chai-ged sand on this 

 contract is interestiug, on account of the difficult nature of the 

 work, and the outlet chamber is most iiiteresting on account of 

 the novelty of the design, there being nothing like it, as far as 

 the author is aware, on any other works hitherto constructed. 

 For draining the w^ater-charged sand nine centrifugal pumps were 

 used with six-inch to nine-inch pipes. Pumping wells were sunk 

 to one side of the sewer trench, and close timbered to the founda- 

 tion level ; the sumps below this level, a few feet in depth, being 

 steined with concrete to prevent any water entering except through 

 a pipe built in the concrete and connected with the sub-duct laid 

 along the centre of the sewer trench and tunnels. The sub-duct 

 consisted of nine-inch earthenware pipes laid in hard wood boxes 

 open at the top and packed with broken stone. These boxes were 

 made w^atertight, and the sides were carried up about two inches 

 above the foundation level, so as to prevent any water entering 

 from below that level, except at the end of the duct, which was 

 always kept some distance ahead of the concrete work. During 

 the construction of the sewer, openings through the concrete 

 were left over the sub-duct at intervals of two hundred feet, and 

 lines with rakes attached were passed through from one to theother, 

 and these lines were occasionally pulled backwards and forwards 

 to keep the pipes clear of silt or other obstruction. Two travel- 

 ling cranes with thirty feet jibs were used for raising the sand 

 from the trenches, which were sunk with a batter of one in eight 

 and close timbered at the sides. 



