168 RAILWAY CONSTRUCTION 



brickwork or masonry. When the well-like excavation has 

 been carried down a few yards, or as far as it can be taken 

 without the risk of the earth falling in upon the sinkers, a strong 

 curb of hard wood or iron of the same diameter as the finished 

 shaft is laid down perfectly level and to exact position, and on 

 this curb the ring or lining of brickwork or masonry is built up 

 to the level of the ground. The first length finished, the excava- 

 tion downwards is resumed, and the interior lining continued, 

 either by allowing the first length to slide down as the material 

 below is gradually removed, and building further lining on the 

 top, or by excavating and propping up the curbing with strong 

 timbers below. When working to the latter method, stout 

 wooden props of convenient length, stepped on to sole-pieces, are 

 adjusted to the under side of the wooden curb above, the material 

 is then removed for the thickness of the brickwork or masonry, 

 and another curb accurately set to level and position ; on this is 

 built a length of lining up to the first curb. 



This work of under-building or under-pinning must be carried 

 out with great care and in segments ; no props must be removed 

 until the curb immediately above is well supported by the new 

 lining, and the inside of the lining must be watched and tested 

 to prevent any tilting. All spaces at the back of the work must 

 be filled in and well packed with hard dry material. As the 

 shaft is continued downwards the mode of working may have to 

 be varied ; different descriptions of material may be encountered, 

 and blasting, shoring, and pumping may each in turn be 

 necessary. 



When down to the full depth, the lower length of the shaft 

 will have to be securely supported by strong timbers, until it 

 can be properly built into and incorporated with the arching of 

 the tunnel or side gallery. 



The completion of the shaft enables the workings to be com- 

 menced on each side, the excavated material can be hoisted to 

 the surface, and building material lowered down. When the 

 tunnel works are finally finished, the lining of the shaft should 

 be carried up until it is 15 or 20 feet above the level of the 

 surface of the ground, and a dome-shaped iron grating placed on 

 the top as a protection against stones or other articles which 

 malicious persons might attempt to throw down the shaft. 



Some shafts are only intended for the temporary purpose of 

 lifting the excavations from below, or lowering building materials 



