”Placed-Stone” Jetty, Stone Weight Coefficients

Hydraulic model tests and some field experience show that placing of armor stone in rubble-mound jetties with the long axis of each stone normal to the surface of the jetty will increase the life and effectiveness of the jetty. The model study demonstrated that when two layers of stones are placed with the long axes perpendicular to the length of the jetty and tilted slightly downward toward the center of the rubble mound, stone-weight coefficients of 5.7 and 6.7 could be obtained with breaking waves and non-breaking waves, respectively. These coefficients compare to 2.8 and 3.5 for similarly rough stones dropped by the pell-mell method. Because the size of stone necessary to withstand the design wave varies inversely with the stone-weight coefficient, the placed-stone method of jetty construction requires stone approximately one half the size required for pell-mell construction.