no-damage criterion (^i.e., the largest waves that did not remove nested 

 armor units from the test sections) were also determined in this manner. 

 Waves slightly smaller than the selected design waves did, at times, 

 remove a few loose armor lonits without endangering the stability of the 

 structure. Photos were made of most wave conditions and breakwater sec- 

 tions were tested. The wave heights generated on the harborside of the 

 breakwater by wave energy transmitted through and over the breakwater 

 were measured at two positions from the structure, one at a distance of 

 X/2 and another at a distance of one wavelength, measured from the 

 centerline of the structure. Breakwater design requires, in addition 

 to accurate data concerning the stability of the armor units, quantita- 

 tive data concerning the thickness and percent voids of the armor-unit 

 layers. Measurements were made on the model sections to determine the 

 percentage of voids in the armor layers tested. The thickness of each 

 armor layer was determined from soundings made before and after placing 

 of the armor units; the total weight of the armor units was determined 

 by weighing the total number of armor units used. The total square feet 

 of surface area of the armor-unit part of the test section was also de- 

 termined. The shape and placing coefficient and the porosity in the 

 cover layers were then determined from the equations 



t=nk^pM| (6-40) 



and 



where 





'AP 



PMl-^i (6-41) 



= the thickness (ft) of n layers of stones of weight 

 W (lb) and specific weight y (Ib/ft^) 



= the shape-placing coefficient 



P = the porosity (P < 1.0) 



W^ = the total weight (lb) of armor units in a cover layer of 

 thickness t required for a given surface area A (sq ft) 



The experimental values of k^p and P for the limestone blocks, ran- 

 domly placed with n = 2, were 1 and 0.41, respectively. Corresponding 

 values of k^p and P for tribar armor units (randomly placed with 

 n = 2), obtained from previous tests, were 1 and 0.54, respectively. 



9^ Summary of Test Results . Stability tests of the tri- 

 bar armor-unit secFion (Fig. 6-18) using a Stillwater level of +4 feet LWD 

 showed that the armor-unit part of the section would be stable for waves 

 to about 16 feet in height; however, for waves 14 feet in height some of 

 the W/2 stones were displaced. It was decided that the W/2 stone 



377 



