SEISMIC METHODS 



889 



As shown in Figure 559, the charges are mounted on adjustable stakes, 

 consisting of a steel rod driven into the ground over which is placed a steel 

 tube with a clamp screw to secure the charge at any desired height. Welded 

 into the top end of this tube is a ^-inch diameter pin over which is placed 

 the expendable support for the charge. This support can be a paper tube 

 or a wooden block with a hole in one end to fit the pin forming the top of 



El- 



Fig. 559. — Method of positioning explosive for air 

 shooting. A, steel stake driven into ground; B, steel 

 tube, adjustable as to height; C, expendable block; D, 

 explosive stick; E, firing wires. 



the stake. The explosive is held by this expendable support, which is 

 replaced with each shot.* 



Several different forms of explosive patterns have been found effective 

 with this method, including a modification of the Munroe shaped charge 

 which was developed into such an effective weapon of war. A flat disc 

 charge composed of an explosive having a high detonation rate, with or 

 without some sort of backing material, produces a very effective flat wave 

 front. Charges having a diameter of 10 to 12 inches and a thickness of y% 



*This is a rather unusual use of explosives, and there are potential hazards 

 involved which are peculiar to the detonating of charges above ground. Every precau- 

 tion should be carefully observed. In particular, personnel and equipment should be 

 at a safe distance or behind barriers for protection against flying particles, etc. The 

 set-up should be sufficiently removed from buildings, power lines, cattle, tanks, etc., to 

 prevent damage from the air blast. 



