LIMITING STRENGTH OF ROCKS UNDER STRESS 
127 
TABLE I 
TABLE GIVING RapIAL DISPLACEMENT OF NICKEL-STEEL JACKET CONTAINING A 
SPECIMEN OF SOLENHOFEN LIMESTONE UNDER VARYING LOADS 
Ui mo un ore 
de ¢ c 
Pounds per | Radial Dis- | Radial Dis- Remarks 
Square Inch} placement | placement 
at Center | over End 
5,100 fo) fo) Diameter of nickel-steel jacket 2.5 in., c=1.25; 
25,500 16 ° length of nickel-steel jacket 3.25 in. 
51,000 34 4 Diameter of rock specimen before loading . 5005 in., 
76,500 50 se) b=.2502 in.; length of rock specimen before 
102,000 76 18 loading 1.5725 in. 
127,000 106 24 Load removed, diam. of specimen at ends .5052 in.; 
153,000 154 38 diam. of specimen at equator .5030 in.; length 
175,000 210 46 1.5437 in. 
200,000 3206 66 Diameter of cylindrical cavities .o50 inch. 
5,100 124 38 Load removed, vertical cavity filled with rock powder, 
1,000 124 38 horizontal cavity distorted. 
1,000 116 37-5 | Longitudinal compression of jacket between 2 in. 
centers .00003 in., per load of 200,000 pounds. 
Last reading taken 45 hours after preceding 
measurement. 
The nickel-steel jacket used contains about 5 per cent of nickel; 
the elastic constants of nickel-steel containing 55 per cent of nickel 
are taken to be #’=10.8X 10° pounds per sq. in., = .327,' values 
not very different from these ordinarily given for steel. 
The constants for the Solenhofen limestone of which the rock 
specimen is made have not been determined; the rock in question 
resembles in its structure and properties black Belgian marble for 
which the elastic constants are #=4.33X10° pounds per sq. in., 
o= .278.? 
In calculating the value of 8 from (11) we may neglect a?/0? 
and since 6?/c?= .04 we find B=.77. Equation (16) then gives 
U' P(pound per sq. in.) 
Cc I.57X 109 Ce) 
Taking p= 200,000 pounds per sq. in. we have U’/c=127 X10 ©. 
The observed radial strain over the center of the specimen is con- 
siderably greater than this. We may attribute the difference to a 
diminution of rigidity. Taking as an extreme case a=o and #=o, 
t Mercadier, Comptes Rendus, 113, 1801. 
2 Adams and Coker, Elastic Constants of Rocks, Carnegie Institution, 1906. 
