984 PROCEEDINGS OF SECTION H. 
The Railway Commissioners decided, in consequence of the 
condition of the timber structures, to replace them with per- 
manent steel and concrete viaducts, the work to extend over four 
years, and the first portion of the work having recently been 
completed, the author explains the method adopted for construc- 
tion and maintenance of traffic. 
The new viaducts are of steel in 29 feet 6 inches spans sup- 
ported on steel trestles, (every tenth pier being carried up solid 
in concrete to counteract brake thrust) and were designed by 
Mr. Firth, Engineer for Existing Lines, the erection being 
entrusted to the author. 
The centre line and level of the new work are the same as the 
old, and in addition to the maintenance of traftic, the prevention 
of damage by possible flood had to be provided for. 
The foundations were formed of concrete, and were put in at a 
distance of 10 feet from the old foundations, for the dual purpose 
of getting into undisturbed ground and not interfering with the 
existing structure. 
Each trestle was supported on two blocks of concrete 6 feet 
3 inches x 4 feet below ground, with a moulded circular top above 
ground 4 feet in diameter. The solid piers were moulded in 
framing in the usual way, and were supported on rectangular 
blocks of concrete, varying in size according to the height of 
piers. The depth of foundations varied from 5 feet to 15 feet, 
according to the nature of the ground and the liability to scour 
in flood-time. 
To facilitate the handling of material a temporary siding was 
laid parallel to the viaduct, and about 30 feet from it. 
The concrete for the piers was deposited through holes in the 
deck of the old viaduct, the material being raised in barrows by a 
whip. Each pier was completed in a day, so that there was no 
joint, and the holding-down bolts for bed-plates and trestles were 
built in. 
The weather being most favourab'e, the excavations, with one 
or two exceptions, required no timbering; and as the concrete 
went in at once, they were subjected to as little exposure to 
weather as possible. 
The concrete for No. 3 viaduct was commenced on February 
19th, 1897, and the whole of the concrete for Nos. 3 and 4 
viaducts was completed on June 18th, 1897. 
In erecting the superstructure and removing the old timber- 
work the considerations were—lst, to reduce all temporary work 
to a minimum ; 2nd, to reduce the risk of damage by flood to a 
minimum ; 3rd, to so arrange that sections of old timber-work 
could be removed and new structure erected between the times of 
ordinary trains, and to avoid Sunday working as much as possible. 
