shows the selected design waves attacking the maximian failing parapet 

 and the resulting failure by sliding. The specific weight of the model 

 concrete was 133.4 pounds per cubic foot. The friction coefficient, f, 

 between the model parapet and rubble breakwater was determined independ- 

 ently, with no wave action, by measuring the horizontal force on the para- 

 pet required to induce sliding. This force, Ff was obtained by a small 

 spring-type force indicator and the friction coefficient was calculated 

 from the relation f = Ff/Wp. The uplift force, U, was then calculated 

 from the relation 



F = Ff = f(Wp - U) (6-43) 



where F is the total calculated wave force, Ff the frictional resist- 

 ance between the parapet and the rubble mound (assuming that the maximum 

 wave force and the corresponding uplift force occur simultaneously) , and 

 Wp the dry weight of the maximum failing parapet. 



(i) Summary of Test Results . The maximum measured force, 

 P, on the parapet corresponded to a prototype force of 2,600 pounds per 

 foot. The parapet was overtopped by 2.5 feet of solid water. Using 

 these values, the equations and the assumed force distributions shown in 

 Figure 6-38, a total maximum force, F, of 3,860 pounds per foot was ob- 

 tained. The weight Wp of the maximum failing parapet was 7,070 pounds, 

 the bottom area of the parapet was 53 square feet, and the friction co- 

 efficient averaged 0.76. The uplift force, calculated from equation 

 (6-43) U = Wp - F/f, was 1,990 pounds per foot. A safety factor of 3 

 for overturning of the parapet was determined by: the equation for rota- 

 tion (Fig. 6-40); a prototype concrete of 144 pounds per cubic foot; a 

 parapet face area of 69.2 square feet; a duration of wave force t, 

 (obtained from the force-time curve) of 3.4 seconds; a prototype weight 

 Wp of 9,960 pounds per foot for the proposed parapet section shown in 

 Figure 6-37; values of a, b, c, and l^ of 5.6, 8.0, and 8.1 feet, 

 and 30,300 pounds per foot seconds squared per foot, respectively; and 

 by graphical integration of the force-time curve. The safety factor for 

 sliding was 1.6. Thus, sliding of the parapet is the critical condition 

 and, considering the simplifying assumptions made in the analysis, it was 

 concluded that the weight of the parapet should be increased by 25 per- 

 cent without increasing the face area, and that structural methods be 

 used; e.g., anchoring the parapet to the cap stones of the breakwater 

 with dowel bars to increase the effective friction coefficient. 



(4) Seawalls (Rubble-Mound and Vertical -Wall Types); Breaking 

 and Nonbreaking Waves . 



(a) Project . Proposed seawalls, Texas City, Texas. 



(b) Reference . Jackson (1966). 



(c) Laboratory . WES. 



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