LVIII. 



\V. E. COOK. 



greater, but the laminated cracks naturally occur more often in 

 the the large pieces and cause a greater percentage increase in 

 weight. 



Results of Tests. 



The results show already, that the pipes are very much stronger 

 against crushing than necessary, only two per cent, having failed 

 to reach the standards demanded, and these are far greater than 

 any pressure which the pipes are called upon to resist. Taking 

 the average depth at which the pipes are laid as 8 feet, and 

 making use of the results obtained by Mr. F. A. Barbour, 1 it is 

 found that the actual pressure of a column of filling 6 inches 

 square, is 128 lbs., the weight of a cubic yard of filling being taken 

 as 28 cwt. 



The following table gives the average crushing strain of pipes 

 tested under the wooden block 6 inches square, while bedded in 

 damp sand as previously described : 



Crushing. 



Internal 



diameter in 



inches. 



Thickness 



in 



inches. 



Weight 



in 

 pounds. 



Standard under 



6 inch square 



block in pounds 



Actual crushing 

 strain under 6 



inch square 

 block in pounds 



6 



5 



8 



36 



3,600 



6,701 



9 



1 5 

 1G 



64 



3,600 



6,675 



12 



1 



97 



2,880 



6,424 



16 



If 



147 



3,240 



5,205 



18 



H 



183 



3,600 



5,349 



21 



H 



240 





4,618 



24 



if 



300 



3,960 



4,965 



In the Sewerage Construction Branch, Public Works Depart- 

 ment, the standards have been raised to the following : — 9 inches 

 to 21 inches =5,000 lbs., 24 inches =5,500 lbs.; owing probably 

 to the fact that the submains laid by that Department are at 

 greater depths than the reticulation sewers. 



1 See paper on "Strength of Sewer Pipes and Actual Earth Pressure/ 

 Vol. cxxxn., Proceeding of Institution of C.E. 



