(g) The Models . Tests on 1;50- and l:55-scale models, de- 

 signed and operated by Froude's law, were conducted in a wave flume 1.0 

 foot wide, 1.5 feet deep, and 76.0 feet long. The test sections were 

 placed at one end of the flume and test waves were generated at the other 

 end by a combination flap-piston wave generator. Wave heights were meas- 

 ured with electrical gages and recorded on an oscillograph. Horizontal 

 wave forces on the parapet were measured on the l:50-scale model with a 

 Statham force gage mounted on the harborside of a hinged gate in a fixed 

 parapet (Figs. 6-34 and 6-35). Force-time curves were recorded on a 

 Brush oscillograph. The hinged gate was 0.5 foot wide (model dimension) 

 and was mounted on an aluminum part of the test section. Lakeward of the 

 parapet, the existing rubble breakwater was modeled of molded concrete 

 blocks and crushed limestone. In the l:55-scale model, the test section 

 of the existing rubble breakwater was simulated throughout with concrete 

 blocks and crushed stone. The model parapet was molded in concrete (Fig. 

 6-36). The bases of the parapet test sections were ground smooth to con- 

 form to the curvature of the breakwater crest. The breakwater cap rocks 

 were also smoothed and placed to provide a uniform bearing surface for 

 the parapet. For these tests the parapet was placed on the breakwater 

 crest without restraints. 



(h) Test Procedures . The dimensions of the proposed para- 

 pet are shown in Figure 6-37. The testing procedure was such that the 

 wave forces on the parapet, caused by the design wave, could be evaluated 

 and a stable parapet could be developed. Storm waves that attack the 

 east-west breakwater vary in period from about 5 to 10 seconds and in 

 height to about 15 feet. However, since the selected Stillwater level 

 was +3 feet LWD, and the proposed crest elevation of the parapet was +15 

 feet, preliminary tests showed that the maximum wave force on the struc- 

 tures would be caused by waves smaller than 15 feet in height. Based on 

 the preliminary tests, a design wave with a 10-second period and a 10.5- 

 foot height was selected. The objectives of this study were to determine 

 the total horizontal force, F, amd the uplift force, U, acting per 

 foot length of parapet. It was assumed that the horizontal force diagram 

 was triangular (Fig. 6-38). The maximum force, P, determined with re- 

 spect to time with the force gage (Fig. 6-39) and the maximum instanta- 

 neous force on the force-time curve (with the assumed horizontal force 

 diagram) were used to derive the total horizontal force, F. The hori- 

 zontal force-time curve was also used, with the torque-acceleration equa- 

 tion of motion for a rigid body rotating about a fixed axis (eq. 6-42) to 

 determine the tendency of the parapet to overturn (Fig. 6-40). 



^M Jo Jo 



, , Wbt2 Uct^ 



Pdtdt - + . (6-42) 



2Im 2Im 



The uplift forces on the parapet were estimated by tests in which the 

 weight of the parapet was reduced by small decrements until the waves 

 caused failure by sliding. This parapet section was designated the maxi- 

 mum failing parapet (dimensions are shown in Fig. 6-41) . Figure 6-42 



40 



