STABILITY OF POLOS OVERLAYS FOR REHABILITATION OF 



TRIBAR-ARMORED RUBBLE-MOUND BREAKWATER AND JETTY 



TRUNKS SUBJECTED TO BREAKING WAVES 



PART I: INTRODUCTION 

 Background 



1. The experimental investigation described herein constitutes a por- 

 tion of a research effort to provide engineering data for the effective and 

 economical rehabilitation of rubble-mound breakwaters and jetties. In this 

 study, a rubble-mound breakwater or jetty is defined as a protective structure 

 constructed with a core of quarry-run stone, sand, or slag and protected from 

 wave action by one or more stone underlayers and a cover layer composed of 

 selected quarrystone or specially shaped concrete armor units. 



2. Previous investigations, under Work Unit 31269, "Stability of 

 Breakwaters," have yielded a significant quantity of design information for 

 new construction using quarrystone (Hudson 1958 and Carver 1980 and 1983) , 

 tetrapods, quadripods, tribars, modified cubes, hexapods, and modified tetra- 

 hedrons (Jackson 1968), dolosse (Carver and Davidson 1977 and Carver 1983), 

 and toskane (Carver 1978). Rehabilitation projects on several of the Corps' 

 rubble-mound structures have revealed a total lack of design guidance or even 

 information concerning the interfacing and stability response of armor units 

 that are of dissimilar type and/or size. In the past, selection of new armor 

 type, method of interfacing, and procedures for preparation of the existing 

 section have been based on engineering judgment or, in more recent times, on 

 site-specific model studies. The engineering judgment process can be expen- 

 sive since experience is limited and there is not usually a solid basis for 

 it. This process can lead to recurring failures that cost millions of dollars 

 without a real solution being developed for the long-term problem. Site- 

 specific model studies have provided good singular solutions, but site- 

 specific data usually fail to meet the requirements of other projects (Carver, 

 in preparation) . It is anticipated that the problem will become more acute in 

 future years as rehabilitation of major breakwaters and jetties becomes nec- 

 essary to extend their project life or to meet greater design demands. 



