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<br />ETL 1110-2-120
<br />14 May 1971
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<br />than the design shear, then the computations should be repeated for
<br />a second trial riprap installation, with the stone sizes being greater
<br />or smaller, respectively, than the sizes used in the first trial
<br />computations. The trial-and-error computations should be repeated Until
<br />local boundary and design shears are reasonably equal and further
<br />refinements would not result in a significant change in stone sizes
<br />and riprap layer thickness. Trial-and-error stone sizes should
<br />correspond to 3-inch modules in riprap layer thickness " such as 12,
<br />15, 18, 21, etc. inches. ..
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<br />4. Suggested District Office Procedure. OCE review of the design of
<br />rip rap protection, submitted in accordance with EM 1110-2-1601 guidance,
<br />has in some instances indicated that proper distribution of the' design
<br />eff9rt between engineering disciplines was not accompiished. In"
<br />general, the following procedure should be adopted: ',: .,....:'
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<br />(1) Hydraulic design personnel should make 'sufficient preliminary
<br />hydraulic computations and analyses to determine areas which may' ,c
<br />require ,riprap protection and establish preliminary riprap material
<br />requirements. . . J; "'~'.' '.;~ ,,;;1 .
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<br />(2) Foundation and materials personnel should assess the
<br />physical characteristics of available material,as discussed in
<br />. subparagraph 3a above. ,~!W .
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<br />(3) Hydraulic design personnel'should check the adequacy of
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<br />the available material for use in providing the required riprap
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<br />protection.
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<br />(4) Finally, a coordinated review of the riprap design should be
<br />made by both hydraulic deSign and foundation and materials personnel.,.
<br />and modifications accomplished in the riprap design where indicated: ;.;:..tJi;i,;.....
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<br />5. Design Example. A trapezoidal channel with SO ft bottom width and ~:;';',~'
<br />1 on'2. 5 side slopes for a design discharge of 7,500 cfs is to be ',.' ,,\'.:"i'"
<br />provided in natural sand and gravel materials having an estimated . :;>~!-\.
<br />effective roughness r!lIlge of 0.5 to 0.8 ft. As a first trial, it is '"
<br />assumed that the sides only will be riprapped and the following rip- '.
<br />rap material (Sp. Wt. = 165 lbs per cu ft SSD) will be placed in an
<br />18 inch layer.
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<br />PERCENT LIGHTER
<br />BY WEIGHT (SSD)
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<br />100
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<br />LIMITS OF STONE
<br />WEIGHT-LBS
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