and 20 ra.3 volume, giving a density of 



ZO 



The dike is founded at a depth of 10 m below low tide. It is un- 

 protected and suffers the full violence of the waves of the Cantabrico 

 (fey of Biscay) with maximum heights approximating 9 meters. The dike 

 was initially constructed with a slope of 2 horizontally to 1 vertical- 

 ly but it soon became apparent that this slope was too steep to assure 

 its stability. Slowly and continuously the rock-fill was increased and 

 the slope flattened, reaching stability at a slope of 5 horizontally to 

 1 vertically. 



Appljring the formula under these conditions, we have: 



^2,000 = ^' ^^' ^'' — 5 



Co.98/-0./93)^ (f O ^ 



from which we obtain 



/r= 18.7 



These two values of the coefficient, K = 14<.8 and K = 18 o7, obtained 

 from situations so different as that of a rock-fill of natural stones 

 of 3,000 kgs. weight and that of artificial blocks of 42,000 kgs 

 weight, prove the coefficient is not very variable.. It is, moreover, 

 logical that the rock-fill of artificial blocks be more vulnerable 

 to the beating of the sea than the compact and better joined natural 

 rock-fill because of their great cavities » Therefore, with a slight 

 margin of security, we fix the coefficients K = 15 for the one and 

 K = 19 for the other.. These two coefficients have been satisfactorily 

 tested in numerous dikes of demonstrated stability. 



We have finally the formula 



in which 



Ccos a- sin A P (d-O^ 



P = wei^t of the stones in kilograms 



K = 15 for natural rock-fill dikes 



K = 19 for artificial block dikes 



A = total height of the wave which breaks on the 

 dike, measured in meters 



d = density of the stone, in tons per cubic meter 



a = the angle of the slope of the dike with the 

 horizontal 



Perhaps it might appear strange, at first sight, that the length of 



12 



