Results from the three-dimensional stability tests indicated the most stable 

 plan was Plan 2B, which consisted entirely of 11 -tonne Core-Locs, a constant 

 crest elevation of +8 m CD, and a vertical-face toe trench 1.5 m high. 



Toe Trench Construction 



For the conditions tested in the model, the breakwater was not damaged if a 

 stable toe trench, 1.5 m deep and near vertical, was installed. The model tests 

 were conducted on a fixed bottom, which in nature would be analogous to a 

 smooth rocky bottom in the prototype. An example of a prototype toe trench 

 constructed in a rocky bottom is shown in Figure 20. The seaward face of the 

 trench should be as near vertical as possible. 



No model tests were conducted on stability with a movable bed; therefore, it 

 was not possible to quantify the effects of a sandy bottom on the stability of the 

 toe trench because the model floor was fixed. For structures placed in shallow 

 water the Shore Protection Manual (1984) recommends a toe protection scheme 

 similar to Figure 21, in which a wide trench is constructed and replaced with 

 armor. The Shore Protection Manual suggests constructing the trench horizon- 

 tally 2 times the water depth or 2 to 3 times the design wave height for the most 

 severe scour. 



UNDERLAYER 

 Wu=Wcl/10 



CORE 

 w C= w CL/200Q; 

 to W CL / 6000 



ROWS PATTERN PLACED ARMOR 



smEc 



y BEDROCK SEAFLOOR 



TITLE: CORE-LOC 

 SUGGESTED PLACEMENT OF TOE 

 UNITS AND SECOND COURSE 



DESIGNED BY: JEFF MELBY It 



GEORGE TURK 



DRAWN BY: ROBERT CHAIN JR. 



DATE 01-NOVEMBER-1996 



WATERWAYS EXPERIMENT STATION 



Figure 20. Example of toe trench constructed on rocky bottom 



Chapter 5 Summary 



31 



