SLIDING-FLOOR TECHNIQUE IN TUNNELLING

Press, Volume CII, Issue 30212, 17 August 1963, Page 10

SLIDING-FLOOR TECHNIQUE IN TUNNELLING

Use In Snowy Mountains Project

[Commonwealth News and Information Bureau] CANBERRA. A NEW sliding-floor technique for tunnelling 1 is being used for the first time in Australia in the Snowy Mountains hydro-electric project. The nine-mile tunnel will link the Snowy River at Island Bend with the Geehi River. It is 22ft in diameter and about 2000 ft below the mountain tops. Work began in September, 1962, and 7500 ft of tunnel had been bored by the end of December. The tunnel advances at the rate of 400 ft every six days.

Mr J. W. Redpath, general manager for the contractors, Thiess Bros., said the tunnel should be finished early in 1964, a year ahead of schedule. The sliding flobr carrying rail track was invented in the United States some time ago by Mr Don Jacobs, who is tunnelling consultant to the Snowy River project. Jacobs Associates in San Francisco designed the three floors which Thiess Bros, are using on the Snowy project, one at each working face. The sliding floor eliminates time lost in laying rail at a working face and reduces the time for switching loaded and empty muck trucks. It moves forward and keeps the rail at the tunnel face. This increases time available for drilling, blasting and mucking The sliding floors in use in Australia are the largest in operation anywhere. Each complete floor is 430 ft long and 13ft wide and consists of some 14 sections. Each section is 30ft to 35ft long. The sections are pin-jointed at their ends to form three independent lengths. These sections are each connected with a set of three hydraulic cylinders. Heavy rail is mounted on the outer sides to carry the drill and ventpipe jumbos The centre portion of the

floor carrie* the lighter rail for the Conway mucker and muck cars. A three-way rail switch is mounted on the centre portion of the floor. Empty muck can are brought along the tunnel and switched to one outside set of rails. They are stored here and taken one at a time to the face for loading. When loaded they are taken back and stored on the other set of outside rails until the complete train has been loaded. They are then ready to move out of the tunnel. A self-contained hydraulic unit is mounted at the rear of the floor. The floor moves rather like a caterpillar. The forward set of hydraulic cylinders is extended. Then they are closed and the rear Set of cylinders Is extended. This move* the centre section of the floor forward. The rear set of cylinders is then closed and this moves the rear section forward. Besides keeping the rails up to the working face the sliding floor improves the

switching of muck trucks. The three-way switch is mounted as close to the face as is practicable. Previously muck trucks had to travel in some instances more than 1000 ft before switching. A specially designed elevated track for the muck cars is mounted at the rear of th* sliding floor which enables laid rail to be stored and fed from the rear while the floor is moving forward.