PART IV: WAVE PRESSURE TESTS 



36. Following the determination of an adequate revetment design, wave 

 pressure tests were performed. The purpose of these tests was to provide 

 pressure data necessary to determine the distribution of wave forces for a 

 variety of wave conditions. Based on these data, the most suitable seawall 

 alternative could be chosen and designed to withstand the corresponding re- 

 sultant forces and ensure stability against overturning and sliding. 



37. Tests were conducted at swl's of +2.6, +4.3, +6.9, and +8.6 ft msl 

 for wave periods ranging from 6 to 14 sec. The most severe breaking waves 

 which experimentally could be made to attack the test sections were investi- 

 gated. In addition, selected nonbreaking and prebreaking waves were tested at 

 swl's of +6.9 and +8.6 ft to provide a wide range of wave conditions on which 

 the seawall selection and design could be based. Wave conditions selected for 

 the wave pressure tests are given in Table 1 , 



38. Typical wave pressure oscillograph records for the seawalls and 

 cutoff wall are presented in Figure 8. Wave pressure-time histories indicated 

 that as a wave struck the seawall, it caused a shock pressure (or impact 

 pressure) of large magnitude and short duration, followed by a secondary 

 pressure (or surge pressure) of lesser magnitude and longer duration. Based 

 on experiments conducted with a vertical wall, Bagnold (1939) theorized that 

 these short-duration shock pressures resulted from the rapid compression of an 

 air pocket trapped between the face of a breaking wave and the wall. This 

 shock pressure phenomenon and its occurrence relative to vertical walls has 

 been studied by several investigators (Minikin 1946; Carr 1954; Kamel 1968a, 

 1968b; Garcia 1968). As shown in Figure 8, wave pressure records for the 

 sheet pile cutoff wall are of similar form except for the negative secondary 

 pressures which occurred during wave drawdown. 



Plan R4S1 Test Results 



39. The first series of pressure tests was conducted with the vertical 

 seawall in place. This plan was equipped with 12 transducers located at ele- 

 vations of +22.0, +20.0, +18.0, +16.0, +14.0, +12.0, +10.0, +8.0, +6.5, +1.0, 

 -1.5, and -4.0 ft msl. A profile sketch of this seawall showing transducer 

 locations is shown in Figure 3. 



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