-296 COALFIELDS AND COLLIERIES OF AUSTRALIA. 



^before it could be drawn into place, since the outside of the 

 casting is of greater diameter than the inside. 



A. A. Atkinson gives an account of the sinking of the 

 No. 3 pit of the Stockton colliery,* from which the following 

 is taken. The total depth of the shaft is 290ft. 4in. to the 

 bottom of the seam. The shaft is tubbed to a depth of 281ft. 

 2in. The time occupied in sinking the shaft, including all 

 delays, was about 3 years and 8 months. The first 233ft. 9in. 

 were forced down from the surface ; the rest were inserted by 

 undersetting. One hundred and thirty-five feet six inches of 

 the tubbing was 10ft. inside diameter, but the last 145ft. 8in. 

 was telescoped to 8ft. lOin. To start with, an excavation 

 22ft. deep was made, and supported in the usual way by piling 

 and boarding. The object of this was to give greater facility 

 for building the rings and to enable a length of 21ft. to be 

 forced down in one operation. All tubbing was made of Ijin. 

 thick cast-iron, and 'Uft. high: the strengthening ribs 1 l-8in. 

 wide were placed on the inside, so that the outside could be 

 forced down through the alluvial with the least possible re- 



Fig. 191. Method of forcing-down Cylinders. 



sistance. The 10ft. diameter tubbing was constructed of 

 rings made of 8 segments, while the rings of the 8ft. lOin. 

 tubbing was composed of 6 segments. A strong framework 

 was erected at the top of the shaft to act as a guide to the 

 cylinders, and oblige it to sink down as vertically as possible; 

 it also permitted six rings to be fitted together at a time on 

 the surface. The bottom ring was provided with a cutting 

 edge, so as to force its way through the alluvial. In order 

 to obtain the necessary pressure to force the cylinder down, 

 sand bags were piled up on a platform resting on the cylinder; 

 this w r eight had to be properly distributed. The platform 

 was built up as follows : Planks of soft wood were placed 

 next the iron to act as a cushion; on these, in three tiers, each 

 tier increasing in length till the topmost one was about 40 

 ft., were placed balks of hardwood timber 14in. square. 

 Fig. 191. These main balks were arranged in pairs at the 



^Working Coal under the River Hunter, the Pacific Ocean 

 ^nd its Tidal Waters, near Newcastle, in the State of New 

 South Wales. (T.I.M.E., 1902.) 



