230 TUNNELING 



CHAPTER XX. 



SUBMARINE TUNNELING (Continued). THE 

 MILWAUKEE WATER-WORKS TUNNEL. 



THE new water supply intake tunnel for the city of Mil- 

 waukee, Wis., is one of the most difficult examples of tunnel 

 construction which American engineering practice has afforded. 

 The difficulties were in a large measure unexpected when the 

 work was decided upon and put under way. The tunnel began 

 and ended in a hard, impervious clay, practically a rock, and 

 all the preliminary investigations led to the conclusion that 

 the same favorable material would be encountered for its 

 entire length. With such material a brick-lined tunnel 1\ ft. 

 in diameter presented no unusual problems; but after about 

 1,640 ft had been excavated from the shore end the tunnel 

 ran out of the hard clay, and for the next 600 ft. or more 

 a variety of water-bearing material was encountered, which 

 tried the skill and patience of the engineer to their utmost. 

 Other difficulties were indeed met with, but these were of minor 

 importance in comparison with that of safely and successfully 

 penetrating the water-bearing drift. 



The work of sinking the shore shafts and excavating the 

 first 1,600 ft. of tunnel did not prove especially difficult. A 

 hard, compact, and rock-like clay, bearing very little moisture, 

 was encountered all along, and was blasted and removed in the 

 ordinary manner. The only mishap which occurred with this 

 portion of the work was the destruction of the contractor's 

 boiler plant by fire on Jan. 12, 1891, which allowed the tunnel 

 to fill with water, and delayed work about a month. By 

 Oct. 21, 1891, 1,640 ft. had been driven, averaging about 6| ft. 



