STABILITY OF TOE BERM ARMOR STONE AND TOE BUTTRESSING 

 STONE ON RUBBLE -MOUND BREAKWATERS AND JETTIES 



Physical Model Investigation 



PART I: INTRODUCTION 

 Background 



1. Failure of rubble -mound breakwater and jetty toes is a problem that 

 has plagued a majority of US Army Corps of Engineers (CE) divisions and 

 districts responsible for designing, constructing, and maintaining these 

 structures. Instability and partial failure of a rubble -mound structure's toe 

 does not become evident until it has resulted in damage to the primary armor 

 which has progressed up to or above the still-water level (swl) . 



2. Under the Repair, Evaluation, Maintenance, and Rehabilitation (REMR) 

 Research Program, the US Army Engineer Waterways Experiment Station's Coastal 

 Engineering Research Center was authorized and funded to conduct a work unit 

 under the Construction, Operation, and Maintenance Research Area entitled 

 Rehabilitation of Rubble -Mound Structure Toes. The first objective of this 

 work unit was to gain an understanding of the toe stability problems experi- 

 enced by field designers and determine what research was needed to develop 

 adequate guidance for design of stable rubble -mound toes. The results of a 

 field experience survey, conducted within the CE division and district offices 

 (Markle 1986), are summarized as follows: 



In general, there appear to be three major problem 

 areas with rubble-mound coastal structure toes. One of 

 these pertains to the proper sizing and placement of toe 

 buttressing stone. The purpose of buttressing stone is to 

 stabilize the slope armor by preventing downslope slippage 

 of the armor layer. For the buttressing stones to func- 

 tion properly, they must be of sufficient weight and 

 placed in such a way that they are stable in the wave and 

 flow environment to which the structure is subjected. The 

 second major problem area is with toe berms . A toe berm's 

 primary function is to protect a structure placed on an 

 erodible bottom from being undermined by wave- and/or 

 flow- induced scour. Resisting downslope slippage of the 

 primary slope armor is a secondary function of the toe 

 berm. For a toe berm to function properly, it, like the 

 toe buttressing stone, must be composed of materials and 

 constructed in a manner that will be stable in the 



