Concrete Revetment Mat Systems for Shore Erosion Control on Offshore Embankments

Abstract

ABSTRACT Shore erosion control is a primary consideration in the design and construction of earth embankments for offshore facilities. The information presented here illustrates the cost-effectiveness of precast concrete flexible revetments to prevent shore erosion on artificial islands constructed for offshore petroleum exploration and production in arctic waters. Included in this presentation are the results of design and construction experience gained with monolayer flexible mat systems since the initial introduction of later-generation revetment technology in 1979. The fundamentals of flexible revetment design are outlined, and major emphasis is placed on sound engineering for total system design. Significant findings from performance observations made on existing flexible revetments are given, and the results of wave tests conducted on model mat systems are summarized. Finally, concrete revetment manufacturing processes and construction techniques are briefly described. INTRODUCTION During the past 40 years, a number of precast concrete flexible revetment designs have been developed and used for limited erosion control applications. Only a few of these systems have proven technically adequate and cost-effective. Until recently, none of the patented flexible revetments had been applied successfully on a coastline subjected to heavy wave action. In 1979, a more versatile and effective precast concrete flexible revetment was developed for protecting shorelines with severe wave erosion conditions. This later-generation system is composed of precast (molded) concrete cellular units laced longitudinally and transversely within tension-resisting tendons to form a flexible mat. All future discussions of flexible revetments in this presentation will imply and refer to later-generation technology as described here. Typical concrete cellular units are shown in Figure 1 and a picture of a fabricated mat is presented in Figure 2. An alternate mat design was later introduced that contains only longitudinal tendons. Load transfer in the transverse direction across this mat is provided by interlocks at the corners of the offset concrete units. This mat design depends on the tensile strength of the concrete at the unit interlocks for transverse load transfer. The two types of mats are illustrated in Figure 3. The first application of a later-generation flexible revetment system was made in 1979 on a marine terminal shoreline along a major navigation channel in the Gulf Coast area. The potential of this revetment design was readily noted and carefully evaluated. Within a few months after this project was completed, work was begun on the development of design concepts to extend this technology to sea defense structures, such as breakwaters and coastal facilities exposed to waves of substantial height. A potential application of particular interest in recent years has been shore protection on artificial islands for offshore petroleum exploration and production in arctic waters. In 1980, these recent developments in revetment design were presented to major corporations with interests in arctic offshore petroleum production. Although little or no use has been made of this technology in arctic offshore construction to date, several applications have been made in other areas of the United States and in Europe.