Q 63
January with the Eastern Mercantile Construction Company. Work on the catchwater and tunnel approaches started on the 20th February but it was not until the 15th April and 4th May respectively, that tunnelling on the north and south faces was commenced. General progress on the whole works was very poor and the tunnel was not holed until August 16th. Subsequent progress on the trimming and lining of the tunnel was also poor and the works were not completed until December 13th. The tunnel was driven from both ends by means of pneumatic drills. The average daily footage was 4.14 feet though on many days the length of tunnel driven exceeded ten feet.
The contract comprised the construction of a reinforced cement concrete aqueduct, a short length of catchwater and a tunnel under Tytam Gap. The aqueduct, which will carry the water collected by a future catchwater draining the northern and eastern slopes of Mount Parker, spans a sharp re-entrant and discharges into the catchwater constructed under this contract. The aqueduct is of box section, has three spans of 35′ 0′′ each and is supported on reinforced concrete piers lined out to represent block work. The maximum height of the aqueduct invert above stream bed is 40 feet. The internal dimensions of the aqueduct are:- Height 5' 8", width 4' 8", the walls, roofs and invert being generally 6" thick. It is constructed of 1, 1, 3 cement concrete the exterior being treated with a special sand finish.
An intake dam diverts the stream crossed by the aqueduct into a catchwater of 10.2 square feet in cross section and 333 feet in length. This small catchwater and the aqueduct discharge at the same point into the main catchwater which has a sectional area of thirty-five square feet and a length of 685 feet. The general construction is similar to that of the Dragon's Back Catchwater except that the side walls are constructed of 1.4.8 cement concrete.
The catchwater discharges into a tunnel under Tytam Gap, the length between portals being 559.5 feet. Except for a length totalling 164.25 lineal feet where a lining of 1.2.4 cement concrete of 9′′ minimum thickness was poured, the arched roof of the tunnel is unlined, but the invert and side walls up to springing level of the arch are lined throughout with 1.2.4 cement concrete of 6" minimum thickness. The inside dimensions of the lined tunnel are as follows:- width at invert 7′ 4′′, width at springing level 8' 6", height from invert level to springing level 4' 6", rise of arch 3′ 0′′, dish of invert 0′ 6′′. The tunnel discharges into a stream bed above the main intake