This proceedings, Case Histories of the Design, Construction and Maintenance of Rubble Mound Structures , contains papers presented at a seminar of the same title held in Eureka, California, May 26-27, 1994. This volume is part of a continuing series of proceedings based on the technical workshops and seminars of the Rubble Mound Structures Committee of the Waterways, Port, Coastal, and Ocean Division of the American Society of Civil Engineers. Some of the topics covered include prototype performance and studies, construction and design management, breakwater construction and stability, and case histories as they relate to rubble mound structures.

In 1978, construction of what is now termed the West Breakwater at the Port of Sines, Portugal, was nearing completion when it suffered severe damage from a large storm having significant wave heights estimated at nine meters. In February 1979, a subsequent storm with significant waves near the design height of eleven meters virtually destroyed the breakwater. The breakwater, armored with 40 ton dolosse, was approximately 1.7 km long and extended generally southward from the mainland to provide the primary wave protection for the Port of Sines as shown in Figure 1. Sines is about 120 km south of Lisbon. Water depths of 50 meters exist close to shore at this site making it a viable site for a deep water port. The site is exposed to waves approaching generally from the west to northwest. The spring-tide range is about 3.6 meters. Cargo entering the port includes oil and coal (Dias & Toppler 1993). Petrochemicals and refined petroleum products are exported. Tankers offload their oil at berths 2 and 3 located immediately leeward of the west breakwater shown in Figure 2. With a water depth of 28 meters, berth 2 accommodates tankers up to 350,000 dwt. Berth 1 in the original design could have accommodated tankers up to 500,000 dwt, however, the severe storm damage to the breakwater and a reassessment of port development vis-a-vis changes in the world's tanker fleet resulted in abandoning berth 1. In addition to providing berths itself, the west breakwater shelters a number of other facilities within the harbor complex including the refined products loading berths, coal terminal, break bulk and the proposed container cargoes.

Rubblemound structures protected from wave action by a layer of quarried rock (stones) are the most common form of breakwaters. While extensive guidelines and procedures exist to select the size of stone there is very little information available on procedures to be followed to assure the quality of the in-place stone. This subject is not covered in depth in the principal breakwater design manuals such as the U.S. Army Corps of Engineers Shore Protection Manual (1984). However, review of existing breakwaters show that deterioration of the stone is a common problem and some projects have experienced very serious difficulties in assuring the placement of durable stone. Review of construction specifications used throughout the world shows considerable variability in testing procedures required to define properties of the stone and different criteria to measure acceptability of a stone. In response to these issues a two-day seminar was held in Cleveland, Ohio on 22 and 23 May 1991, sponsored by the Rubblemound Structures Committee of the Waterways, Port, Coastal, and Ocean Division of the American Society of Civil Engineers. Cleveland was an important location because of the serious deterioration of some of the stones placed on the Cleveland breakwater.

This book is derived from a Seminar at the Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg, Mississippi held on November 7-8, 1989. It presents a state-of-the-art review of the design, analysis, and hydraulic model testing of concrete armor units used in coastal rubble mound structures. In addition, prototypes of concrete armor units are presented and analyzed as are current design procedures. Finally, research needs are identified.

The standard design for a rubble-mound breakwater as reported in recent text books and manuals has consisted of a core of rubble quarry-run that is protected from wave action by two layers of relatively large quarried stone or concrete units. Filter layers of intermediate size stone are recommended beneath the armour layer to prevent loss of the core material through the armour. The pioneering work of Hudson provides coefficients for a formula that allowed widespread use of this design concept throughout the world. A breakwater of this form tends to require the smallest volume of stone; however, it may not represent the least cost structure for a specific location because of the cost and availability of local materials. Recently, design engineers and hydraulic laboratories have given considerable attention to alternative forms of rubble mound structures. The objective of this work has been to minimize cost while maintaining the same or improved level of stability when the breakwater is subjected to extreme wave conditions. Principally, emphasis has been given to the utilization of locally available quarried stone and to maximizing the use of the full yield of a local quarry. This has required the design of breakwaters using smaller armour stone and a wider range of sizes than was used in the more conventional breakwater. These designs have also given consideration to the realities of construction and the limitation of construction equipment on the assumption that cost savings will be achieved with relatively simple construction methods. Clearly the use of smaller armour stones requires a change in other properties or characteristics of the armour layer, compared to a conventional design, in order to achieve the same stability. The principal characteristics of a berm breakwater are the high permeability of the armour-layer and the significantly larger volume of armour. Berm breakwaters generally consist of a relatively large and permeable mass of armour stone (of smaller size than required for a conventional design).

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A survey of existing Corps breakwaters with concrete armor units and hydraulic model tests of rubble-mound breakwater trunk sections protected with dolosse were conducted to determine the effects of broken armor units on breakwater stability and to establish some criteria by which decisions can be made as to when maintenance and rehabilitation work should be initiated on damaged concrete armor unit cover layers. The survey revealed that where good engineering designs were used, prototype breakage has been random and has not exceeded about 3 percent of the total number of units placed. The model tests, conducted with both breaking and nonbreaking waves with no overtopping, revealed the percent breakage can be quite a bit higher than 3 percent before the overall functional integrity of dolos cover layers is affected.