(in Hawaii) to the 6.35-kilogram (14 pounds) Gobi block. Size can 

 usually be adjusted according to need; type selection may depend on 

 armor unit stability for a given structure. Stability coefficients 

 are given in the SPM. 



Concrete armor units have been tested and are used both for rubble- 

 mound structures (usually porous near the top) and for riprap or revet- 

 ment structures (usually impermeable to wave transmission) . Most tests 

 have been for permeable rubble-mound structures. 



(!) Permeable Structures . Jackson (1968a) tested several armor 

 units for runup and stability (Fig. 43). Further details of the armor 

 units are given in the SPM or Hudson (1974). Wave conditions used in 

 the tests were limited mostly to relative depths of d s /H^ * 5.0. The 

 relative armor size has been calculated for this study as H^/k r , using, 

 for kp, the length dimensions shown in Figure 43. These dimensions 

 are heights of armor units in all cases. Jackson used rubble-mound 

 structures, and relative core heights calculated from photos in his study 

 have values of h c /d s « 1.14, except for a structure with one layer of 

 modified cubes on a 1 on 3 slope which had a value of h-/d„ as 1.4. 

 Jackson's sketches of all structure cross sections indicate the core 

 and lower underlayer to be below SWL. Since his photos show other cases, 

 it is unclear what the values would be for the remaining situations. 



Jackson's data, after conversion to deepwater variables, were com- 

 pared to the smooth-slope curves. Results are summarized in Table 11. 

 Each r value in the table is an average of r values determined for 

 two or three wave steepnesses and for the slope and value of dL/H' 

 noted. u 





Table 11. S 



urnmary of r values (after Jacks 



n, 1968a). 











Armor unit and placement method 



Armor layer 

 thickness 

 CNo. of units) 



CH^/k r for dg/H^ = 5.0) 





r values for < 



,/H,; - 5.0 1 







1 on 1.5 



1 on 1.75 



1 on 2.0 



1 on 2.25 



1 on 3.0 



Avg 



Concrete tetrapod 

 Random 

 Uniform 



Leadite tetrapod 

 Uniform 



2 

 2 



2 



2.30 

 2.30 



2.25 



0.45 

 0.51 



0.50 



0.40 

 0.51 



0.49 



0.39 



0.41 

 0.51 



0.50 



Concrete quadripod 

 Random 

 Uniform 



2 

 2 



2.90 

 2.90 



0.51 

 0.49 



:::: 



0.47 

 0.46 



:::: 



0.49 

 0.51 



0.49 

 0.49 



Lecdite tribar 

 Random 

 Uniform 



2 



1 



2.S6 

 2.86 



0.44 

 0.50 



:::: 



0.4S 

 0.5O 3 





0.40 3 



0.43 

 0.50 



Modified leadite cube 

 Random 

 Uniform 



2 



1 



2.99 

 2.99 



0.44 

 0.62 



:::: 



0.4S 

 0.73* 



:::: 



0.48 

 0.55 



0.46 

 0.63 



Leadite hexapod 

 Random 

 Uniform 



2 

 1 



1.72 

 1.72 



0.41 

 0.52 





0.44 

 0.51 



:::: 



0.48 



0.44 

 0.52 



Solid concrete tetrahedron 

 Uniform 



Perforated concrete tetrahedron 

 Uniform 



2 

 2 



2.31 

 2.24 



0.50 



0.58 



0.S3 



0.S7 



0.54 



0.56 

 0.52 



Solid leadite tetrahedron 

 Uniform 



Perforated leadite tetrahedron 

 Uniform 



2 

 2 



2.29 

 2.22 



0.S4 

 0.50 



.... 



0.54 

 0.S1 



.... 



.... 



0.54 

 0.51 



l dj ■ 0.61 meter (2 feet). 

 2 Mo data available. 



Vh; - 3.0. 



""./Hi * 4-0. 



87 



