Pa = 2.66 g/cm-\ and Dg^/Di^ = 1.53. The mass distribution, plotted as percent finer by 

 mass, is shown in Figure 7. 1 . The median mass was computed from a 200 stone sample 

 as the value where half the total mass in the sample was greater. For comparison, the 

 median mass by count for a 200 stone sample was M^q^ = 128 g (i.e. half the stones 

 weighed less). This latter value was not used in this thesis, although it is sometimes 

 used in the field. The riprap followed the widest recommendation of the SPM (1984) of 

 approximately 0. 125M5o< M < 4M^q. For all series, the underlayer or filter layer had a 

 gradation of Dgj/Z),; = 1.32 and was sized such that (M^q)^^^ I {M^q)^,,^^ = 25 and 

 (D5o),™../(Z)5oW. = 2.9. 













J 

























■|Underlayer 



/ 

















/ 















«0 











i 



r 















/ 







(0 











' 

















1 







ffi 











1 

































J 













r 



_/ 









•S 40 - 



iRipraplllll 











/ 



1 























a. 



on - 







































/ 



f 















I 











- 







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- 





.'■^ 











10 100 



Mass (g) 



1000 



Figure 7. 1 . Stone mass distributions for riprap and underlayer 



130 



