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The three classes of riprap described in appendix B, section 10-2.1, are intended to provide a light, medium, and heavy class of riprap of sat- isfactory gradation. The three classes shown in the sample specifications might not provide a suitable range of riprap size for conditions in same States. Individual specifications might have heavier or lighter classes or they might provide the to11awing single gradation referenced to the 50 percent size (k). Size ot stone Percent of total weight smaller than the given size 3k 100 2k lk 80 50 O.lk not to exceed 10 Each load of riprap should be reasonably well graded trom the smallest to the maximum size specified. Stones smaller than the specified 10 per- cent size and spans should not be permitted in an amount exceeding 10 percent by weight of each load. Gradation of the riprap being placed is cootrolled by visual inspec- tion. To aid the inspector's judgment, two or more slUllples ot riprap ot the specified gradation should be prepared by sorting, weighins and remixing in proper proportions. Each 8lUIIp1e should weigh about 5 tons. One sample should be placed at the quarry and one slUllple at the construc- tion site. The sample at the construction site could be a part of the finished riprap blanket. These samples should be used as a frequent reference for judging the gradation of' the riprap supplied. Methods for determining the gradation of gravel-paved streambeds are discussed in reference 19. These methods can be adapted to checking grada- tion of riprap in place. 3.2 - Hand-Placed Riprap Stone used tor hand-placed riprap should be of better quality than specified for dumped riprap. Stone should be roughly square or rectangular to facilitate laying them up. The gradation curves for dumped riprap are not applicable. Only enough rock fragments to fill the openings between the larger stone should be permitted. (See reference 2, p. 264.) 11-22 I I ell . . I I eJ l I I , l ~ l I l I I ~ I I . e