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<br /> <br />r' <br /> <br />, <br /> <br /> <br />c <br /> <br />EM 1110-Z-1601 <br />1 July 70 <br /> <br />ilters specified in EM 1110-Z-1901. <br />(7) The bulk volume of stone lighter than the W 15 stone should not ex- <br />ceed the volume of voids in r~vetment without this lighter stone. <br />(8) W 0 to W Z5 stone may be used instead of W 15 stone in criteria (5), <br />(6). and (7) if desirable to better utilize available stone sizes. Design memo- <br />randa and specifications should indicate the permissible stone gradation <br />limits by a tabulation, illustrated as follows: <br /> <br />Example <br />Percent Lighter <br />by Wei~ht (SSD) <br /> <br />100 <br /> <br />50 <br /> <br />15 <br /> <br />Gradation <br />Limits of Stone <br />Weight. lb <br /> <br />Z60-640 <br /> <br />130-Z00 <br /> <br />40-150 <br /> <br />(: <br /> <br />i. Riprap Layer Thickness. All stones should be contained reason- <br />ably well within the riprap layer thickness to provide maximum resistance <br />against erosive for.ces. Oversize stones, even in isolated spots. may cause <br />riprap failure by precluding mutual support between individual stones. pro- <br />viding large voids that expose filter and bedding materials. and creating ex- <br />cessive local turbulence that removes smaller stones. Small amounts of <br />oversize stone should be removed individually and replaced with proper size <br />stones. When a quarry produces a large amount of oversize stone, consider- <br />ation should be given to changing the quarrying method. using a grizzly to <br />remove the oversize stone, obtaining the stone from another source, or in- <br />creasing the riprap layer thickness to contain the larger stone. The follow- <br />ing criteria apply to the riprap layer thickness: <br />, <br />(1) It should not be less than the spherical diameter of the upper limit <br />W 100 stone or less than 1.5 times the spherical diameter of the upper limit <br />W 50 stone, whichever results in the greater thickness. <br />(Z) It should not be less than 1Z in. for practical placement. <br />(3) The thickness determined by either (1) or (Z) should be increased <br /> <br />'" <br /> <br />43 <br /> <br />14i(3) <br />