Repair, Evaluation, Maintenance, and Rehabilitation Research Program. Stability of Rubble-Mound Breakwater and Jetty Toes; Survey of Field Experience.

The purpose of this survey of field experience is to present an overview of the coastal rubble-mound breakwaters and jetties built and/or maintained by the US Army Corps of Engineers that have or have had stability problems related to structure toes. Extensive discussions with US Army Corps of Engineers division and district personnel, along with review of district office files, revealed that rubble-mound toe stability is a major repair and rehabilitation problem that can be divided into two major design categories: (a) design of buttressing stone placed at the toe of an armor slope to prevent downslope slippage of primary armor, and (b) design of toe berm armor size and geometry that will be stable for incident wave and flow conditions and will prevent, or at least slow down, scour and undermining of a structure's toe. No firm guidance presently exists to aid Corps personnel with these two design problems., and most design work is carried out using limited local field experience on past successes and failures. Design guidance in this area is urgently needed and will be addressed through the use of coastal hydraulic model tests authorized and funded under the Repair, Evaluation, Maintenance, and Rehabilitation Research Program Work Unit titled 'Rehabilitation of Rubble-Mound Structure Toes'. This field survey was conducted under authority of this same work unit.