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<br />Design Guideline 4 <br /> <br />Articulated Concrete Block System <br /> <br />Introduction <br /> <br />Articulated concrete block systems (ACB's) provide a flexible alternative to riprap, gab ions <br />and rigid revetments. These systems consist of preformed units which either interlock or are <br />held together by steel rods or cables (see Figure 4.1), or abut together to form a continuous <br />blanket or mat. This design guideline considers two applications of ACB's: Application 1 - <br />bankline and abutment revetment and bed armor; and Application 2 - pier scour protection. <br /> <br />There is little experience with the use of articulated block systems as a scour counter- <br />measure for bridge piers alone. More frequently, these systems have been used for <br />revetments and channel armoring where the mat is placed across the entire channel width <br />and keyed into the abutments or bank protection. For this reason, guidelines for placing <br />articulated block systems at banklines and channels are well documented, but there are few <br />published guidelines on the installation of these systems around bridge piers. Where <br />articulated block systems have been installed as a countermeasure for scour at bridge <br />piers, cable-tied concrete mats have more often been used. <br /> <br />Specifications and design guidelines for installation and anchoring of ACB's are documented <br />in Brown and Clyde (HEC-11) (1989) and guidelines on the selection and design of filter <br />material can be found in HEC-11 (1989) and Holtz et al. (FHWA HI-95-038) (1995). HEC-11 <br />directs the designer to the manufacturer's literature for the selection of appropriate block <br />sizes for a given hydraulic condition. Manufacturers of ACB's have a responsibility to test <br />their products and to develop design criteria based on the results from these tests. Since <br />ACB's vary in shape and performance from one proprietary system to the next, each system <br />will have unique design criteria. A procedure to develop hydraulic design criteria for ACB's <br />given the appropriate performance data for a particular block system is presented in this <br />section. <br /> <br /> <br /> <br />Figure 4.1 Examples of interlocking block and cable-tied block systems (left, courtesy <br />American Excelsior; right, courtesy Armortec) <br /> <br />Background <br /> <br />Beginning in 1983, a group of agencies of the federal government, led by the Federal <br />Highway Administration (FHWA), initiated a multi-year research and testing program in an <br />effort to determine, quantitatively, the performance and reliability of commercially available <br /> <br />4.3 <br />