The Railway Conquest of the World

by Frederick Arthur Ambrose Talbot

THE HOOKINA CREEK BRIDGE

In the summer the watercourse is dry. Note the measures adopted to protect the piers from the force of the flood waters.

TWO VIEWS ON THE SOUTH AUSTRALIAN GOVERNMENT RAILWAYS

The task was commenced in July 1908 under the guidance of Mr. James Fraser, M.INST.C.E., the engineer-in-chief for existing lines, to whom I am indebted for this information, and in a short time 1000 men were engaged in boring the tunnels and making the deep, heavy cuts through the sandstone rock. All tunnels were attacked simultaneously, and the blasting assumed heavy proportions. In one case a shaft was sunk practically to formation-level. When completed it was charged with about 10,000 pounds of blasting powder and 125 pounds of gelignite. It was fired electrically, and the splitting force of the explosives dislodged 35,000 tons of rock. In another case 1000 pounds of blasting powder were tamped home in the face of a cliff, and 10,000 tons of rock were shivered to be used for embanking purposes.

In order to rush the work through at tip-top speed, special arrangements were made to facilitate the handling of the necessary supplies and men, as well as the operation of the tools. As the new line passed 350 feet below the old line, connection between the two at this crossing was effected by means of a funicular railway with a grade of 1 in 1.87. The material was brought by rail to the upper end of this temporary line, and from a special siding was dispatched direct on to the works. A small electric generating station was set up, and wires for the transmission of current for power and lighting were strung along the route from end to end to compress the air to drive the rock drills, for the motors actuating the ventilating fans and also the water-pumps.

The scheme as originally planned provided for the building of 6 miles 858 yards of new double track, which represented a saving of 22 yards upon the line that was being displaced, though the curves and grades were easier. It was estimated that the earthworks would involve the handling of 466,000 cubic yards apart from the tunnel borings. Eleven tunnels were planned, representing a total length of 2,991 yards, but during the work it was decided to cut out one tunnel as the rock was found to be shattered. Consequently it was converted into an open cutting, the sides of which are 132 feet high. Some idea of the speed with which the task was pushed forward may be gauged from the fact that in 11 months 410,000 cubic yards of excavation were completed, 1¼ miles of permanent way were laid with a single line, and 1,430 yards of the tunnelling were completed. The total cost of the work was estimated at £256,000, or $1,280,000. Its recent completion, although it relegates an imposing engineering achievement to the limbo of things that were, has resulted in the creation of another achievement equally as notable.

In building the north coast line which connects Sydney with the Queensland border, a feat of a totally different character from the zigzag was completed. This is the massive bridge, 3000 feet in length, which carries the track across the Hawkesbury River, 36 miles distant from the capital. It is divided into seven spans, each of which measures 416 feet in length, supported on substantial masonry piers.

The erection of this structure, which still ranks as the largest work of its type in Australia, occasioned considerable difficulty, both in regard to the piers and the setting of the steel-work into position. Indeed, it is doubtful as to which section of the work provoked the greater anxiety. The difficulty with the piers was the great depth to which the engineers had to descend to secure a foundation, because in mid-stream the 40 feet of water flows over a bed of mud ranging up to 120 feet in thickness.

The only practicable means by which this essential subaqueous work could be carried out was by sinking a huge steel cylinder filled with concrete. The bottom section of this huge tub, or caisson, as it is called, was closed, and after it was completed on shore it was towed out to the site where the pier was to be erected and sunk by the introduction of the concrete. The under side of the caisson was fitted with a knife edge, by means of which it could cut its way through the soft soil, the driving force for this purpose being the weight of the superimposed concrete. The mud over the area representing the superficies of the cylinder bottom was removed from the inside to enable the mass to settle down. The steel shell was built up continually from the water-level in rings, until a solid foundation was gained. When this was reached and deemed satisfactory the spaces through which the spoil from below had been withdrawn were likewise filled with concrete, so that the contents of the cylinder really form a huge pillar of concrete homogeneous from end to end.