STABILITY OF POLOS AND TRIBAR OVERLAYS FOR REHABILITATION 



OF STONE-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 No. 31269, "Stability of 

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

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

 pods, quadripods, tribars, modified cubes, hexapods, and modified tetrahedrons 

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

 toskane (Headquarters, US Army Corps of Engineers 1978). Rehabilitation proj- 

 ects 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 judg- 

 ment or, more recently, on site-specific model studies. The engineering judg- 

 ment process may be expensive since experience is limited and a solid basis 

 seldom exists. This process can lead to recurring failures that cost millions 

 of dollars without developing a real solution to 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 

 1988) . It is anticipated that the problem will become more acute in future 

 years as rehabilitation of major breakwaters and jetties becomes necessary to 

 extend their project life or to meet greater design demands. 



