CHAPTER V 



EXCAVATION OF SUBAQUEOUS ROCKS BY BLASTING 

 COMPARISO-N OF THE TWO METHODS 



SUBMERGED rock can be removed by small successive blasts 

 fired in rounds as quickly as the holes are drilled and charged. 

 Such a method is used in the excavation of submerged rock encoun- 

 tered at a comparatively shallow depth and for some years has been 

 the most common method of removing subaqueous rock. Blasting 

 rock in connection with dredging was done in England years ago. 

 The Encyclopedia Brittanica mentions the works of Rennie at Newry 

 and Stevensons at Ballyshannon as executed in this manner. The 

 same method was afterward extensively used by Mr. William Cubitt 

 on the Severn. It was described by Mr. Evans in the Proc. Inst. 

 of C. E., Vol. IV, and condensed as follows: 



Drilling Plants. In removing marl beds along the channel of 

 the Severn, after the dredges had been unsuccessfully employed, 

 new methods were tried, one of them consisting in scraping the 

 bottom of the channel with a plow, another to drive into the 

 hard soil iron rods, so as to loosen the material. However, it was 

 decided that the only possible way was to recourse to blasting. 

 For this purpose, from a raft moored into the river w^ere lowered 

 iron pipes 3J in. in diameter and sunk well into the marl. Through 

 these pipe holes were bored first with a IJ-in. jumper and then 

 with an auger. The holes were bored 6 ft. apart each way. The 

 cartridges were formed in the ordinary way with canvas and fired 

 with Blickford fuses. 



In breaking rock by blasting on the Rhine River, between Bingen 

 and Coblenz, in the year 1863, Mr. Hipp successfully employed 

 a new device for drilling holes, which has been in constant service 

 until very recently. This consists of a drilling machine in which the 

 drill 5 meters long was fastened to the axis of the piston. It was 

 raised by steam power and let fall by its own weight. The weight 

 of the rod w r as from 150 to 200 kg. and the machine was able to 



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