RAILROAD CONSTRUCTION 269 



ROCK EXCAVATION 



Previous to excavation rock is broken by an explosive into 

 fragments that can be handled readily. 



It is transported chiefly in carts, wagons and cars, although 

 it may be moved for short distances on wheelbarrows or thrown 

 out by hand in shallow cuts. 



A cubic yard, place measure, of rock increases from 60 to 

 80 per cent when broken up. On an average only 60 per cent 

 as much yardage of rock can be hauled as of earth. 



Payment for the removal of rock which is classified as "loose 

 rock" and "solid rock" is on the basis of the cubic yard, "in 

 place." 



A. BLASTING 



The holes in which charges are placed are usually bored with 

 hand drills. The diameter and spacing of holes depend upon the 

 kind of explosive used, the character of the rock and the method 

 of handling it. As a rule, the holes are spaced a distance apart 

 equal to their depth, although in hard rock they are often placed 

 closer together. Close spacing increases the amount of drill 

 work required and the quantity of explosive used, although it 

 is often more economical because of the smaller size of material, 

 which makes handling cheaper. 



Drilling. — Hand drilling is preferred for logging work because 

 of the limited amount of rock moved and the difiticulties of trans- 

 porting drilling machinery and equipment to the site of the work. 



There are three forms of drills used for hand work; namely, 

 the "churn drill," the "jumper drill" and the "hand drill." 



Churn Drill. — ■ This is the most economical form of drill for 

 holes up to 30 feet in depth and from i^ to 2^ inches in diameter. 



The drill consists of a i\- or i|-inch round iron bar of the 

 required length, on one end of which is welded a steel chisel bit 

 from 30 to 100 per cent wider than the diameter of the rod. 

 Several rods of different lengths are required for drilling a deep 

 hole. 



The drill is operated by raising it from 18 to 24 inches and 

 allowing it to drop, the weight of the drill furnishing the power. 



