32 BULLETIN 1077, U. S. DEPARTMENT OF AGRICULTURE. 



mainder of the work. The following methods may be employed: 

 (1) Unloading by hand into wagons, trucks, or into light movable 

 bodies which are hung against the side of the car and from which 

 the material is dumped into wagons or trucks; (2) mechanical un- 

 loaders, using belt conveyors, discharging into wagons or trucks; 

 (3) bucket elevators or skip hoists from pits below the track, dis- 

 charging into bins; (4) a clam-shell bucket on a stiff-leg, or guy-line 

 derrick; (5) a clam-shell bucket on an auto crane or locomotive 

 crane. (See Fig. 1, PL VI.) The first three of these methods can 

 be employed to advantage where a comparatively small amount of 

 material is to be handled and this material can be obtained in bot- 

 tom dump gondola or hopper cars. They can only be used, how- 

 ever, where the materials, are distributed on the subgrade or placed 

 in stock piles on the shoulders of the road at short intervals. None 

 of them affords any storage capacity at the unloading station. 



Pavement construction is seasonal work. The peak demand for 

 materials naturally occurs during the midst of the construction sea- 

 son, and it frequently happens that because of this increased demand 

 regular deliveries and sufficient quantities of materials can not be 

 obtained for the work at hand. With uncertain transportation 

 facilities and a known shortage of railroad equipment for normal 

 business conditions, the storing of materials is practically imperative 

 if work is to proceed without interruption during the construction 

 season. The storing of a considerable quantity of materials can best 

 be done by means of a clam-shell bucket on either a derrick or a 

 crane. On account of its ability to swing through a complete circle, 

 a guy-line derrick can store more material than a stiff-leg. If a 

 stiff-leg derrick is used, the maximum storing capacity will be 

 reached by setting the derrick with one leg parallel to the railroad 

 track. Cranes are considerably more flexible in operation than der- 

 ricks, and it is possible to store a large amount of material if the 

 storage piles parallel the track. In their principles of operation 

 auto and locomotive cranes are the same, the only difference being 

 that locomotive cranes are considerably heavier, have longer booms, 

 and operate on railroad tracks. If the reloading bin is stationary, 

 the amount of material that can be stored within reach of the bin 

 without rehandling will depend upon the boom length of the derrick 

 or crane. For large storing capacity a boom length of from 50 to 

 60 feet is desirable. With movable bins, however, good storing 

 capacity without rehandling can be obtained with cranes having a 

 boom length of 30 feet. The use of derricks and cranes combines the 

 labor-saving feature with the storage feature, and where the mate- 

 rials are proportioned or mixed at the unloading yard, their use is 

 practically indispensable. 



