98 NEW YORK STATE MUSEUM 



certain zones in the shaft and tunnel. At some places the solid 

 granite would pop off in slabs with a crackling sound and would 

 sometimes fall quite without warning. These slabs came off quite 

 independently of any rock structure, even breaking directly across 

 the structure quite as well as any other way. Some of the slabs 

 were thin and came to a sharp knife-edge. Injuries from falls of 

 this kind were numerous and they became a serious menace to the 

 workmen, who had to be protected by timbering or other methods. 



xA.t one place this popping became so active that the tunnel itself 

 had to be protected from a sort of stoping process developed by 

 this popping rock. Slabs had a habit of loosening and dropping 

 off continuously. If the loosened ones were scaled oflf one day, new 

 ones would be separated by the next. Thus the danger was a con- 

 stant one. At this particular place stoping of this kind in the 

 roof of the tunnel proceeded to such length that measures had to 

 be taken to stop it by timbering. A steel support was finally installed 

 at this point and was left in place when the tunnel was finished. 



Even after the tunnel was finished, difficulty was made by this 

 strained rock condition. When the tunnel was filled and put under 

 operating pressure a pronounced leak developed on the Moodna side 

 under Storm King mountain. Upon unwatering the tunnel the con- 

 crete lining at the Hudson river end of the Moodna pressure tunnel 

 was found to be ruptured. Study of the possible causes led to 

 the conclusion that rock strain aided by the bursting pressure of the 

 aqueduct water was the cause, the tunnel at that point cutting 

 through a strain zone at too shallow a depth to remain stable with 

 the abnormal conditions then in control. 



It was finally remedied by constructing a small portion of this 

 end of the Moodna tunnel, where it joins the west shaft of the much 

 deeper Hudson River pressure tunnel, at a greater depth in order 

 to obtain more stable conditions and a better balance between burst- 

 ing pressure aided by strained rock on the one hand and the load 

 of rock above and its strength on the other. The corrected tunnel 

 has since given no trouble. 



A somewhat similar condition which was, however, .corrected 

 more simply, was developed also on the Breakneck side. 



Bull Hill tunnel. Bull hill, or Mt Taurus, forms the second 

 mountain ridge on the east side of the river toward the south and 

 the aqueduct penetrates this from one side to the other at about 400 

 feet above sea level. The rock penetrated is of considerable variety 

 in a minor way. But there is nothing beyond the complexities 



