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Chapter 4: HEC 11 <br />►I Design Guidelines for Rock Riprap <br />Go to Chapter 5 <br />As defined in Chapter 2, rock riprap consists of a well graded mixture of rock, broken concrete, <br />or other material, dumped or hand placed to prevent erosion, scour, or sloughing of a structure <br />or embankment. In the context of this chapter, the term rock riprap is used to refer to both rock <br />and rubble riprap. <br />Rock riprap is the most widely used and desirable type of revetment in the United States. The <br />term "riprap" connotes rock riprap. The effectiveness of rock riprap has been well established <br />where it is properly installed, of adequate size and suitable gradation. Riprap materials include <br />quarry-run rock, rubble, or other locally available materials. Performance characteristics of rock <br />and rubble riprap are reviewed in Section 2.1.1. <br />This chapter contains design guidelines for the design of rock riprap. Guidelines are provided <br />for: <br />• Rock size, <br />• Rock gradation, <br />• Riprap layer thickness, <br />• Filter design, <br />• Material quality, <br />• Edge treatment, and <br />• Construction considerations. <br />In addition, typical construction details are illustrated. In most cases, the guidelines presented <br />apply equally to rock and rubble riprap. Sample specifications for rock riprap are included in <br />Appendix A. <br />4.1 Rock Size <br />The stability of a particular riprap particle is a function of its size, expressed either in terms of its <br />weight or equivalent diameter. In the following sections, relationships are presented for <br />evaluating the riprap size required to resist particle and wave erosion forces. <br />4.1.1 Particle Erosion <br />In Chapter 1, riprap failure modes were identified as particle erosion, translational <br />slide, modified slump, and slump. Translational slide, modified slump, and slump are <br />slope or soils processes. Particle erosion is a hydraulic phenomenon which results <br />