UISTOKY OF CIVIL ENGINEERING IN NEW SOUTU WALES. 607 



low ground liable to flood, near the Murrumbidgee River, form 

 the approaches to the Wagga Wagga iron bridge. These extensive 

 timber structures comprise six viaducts, the details of wliich are 

 given in the following table : — 



The superstructure is of ironbark. All the spans are twenty- 

 eiglit feet six inches in the clear, formed of beams twenty-nine 

 feet six inches long bolted to corbels fixed to the timber piers. 

 The piers are constructed of round timber piles. In fifty-eight 

 piers the piles are driven into the ground to depths varying from 

 fourteen to fifty-seven feet, and in two hundred and sixty-four 

 piers the piles are tenoned into sills bedded in concrete at depths 

 varying from six feet to eight feet below the surface of the ground. 

 The dilficulty of obtaining ironbark timber for the whole structure 

 in the siiort space of time allowed for its erection necessitated the 

 use of other kinds of timber for the piers, such as stringy bark, 

 ash, messmate, apple, box, spotted and white gum, &c., of whicli 

 a large proportion had to be cut when the sap was up instead of 

 during the winter months. In consequence of this the dry rot 

 soon appeared in a certain proportion of the piles, and this decay, 

 together with the cavity or pipe in some of them, has reduced 

 their sectional area. White ants, which have been found in some 

 of the piles, have been successfully eradicated by the use of 

 kerosene and a mixture of arsenic and tallow. 



These viaducts were tested by the Bridges Commission, 

 and the maximum deflection 

 each weighing .sixty-three tons 

 quarters, was 59 inches. The 



main girders continuous over four openings, each 

 clear span of one hundred and fifty feet. The m? 



observed with two engines, 

 sixteen hundredweight three 

 bridge consists of two lattice 

 having a 

 n srirders 



are fourteen feet apart in the clear, each forming a con- 

 tinuous girder six hundred and thirty-nine feet long, extending 

 over three intermediate piers. Between the lattice girders trans- 

 verse or roadway girders are placed at a distance of three feet 

 from centre to centre. The piers are one hundred and fifty-nine 

 feet from centre to centre, and, together with the abutments, con- 

 sist of cast-iron cylinders nine feet in diameter, filled with cement 

 concrete. Tlie top cylinders of each pier are braced together with 



