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<br /> <br />. <br /> <br />EM 1110-2-1601 <br />1 July 70 <br /> <br />C' <br />'Equations 33 and 34 are readily solved by the use of plates 35 and 36. Th~ <br />local boundary shear at any point on the sides and bottom of a riprap-lined <br />channel should not exceed the design values determined by equations 33 and <br />34. . Sample computations for the determination of stone size for a riprap- <br />, lined trapezoidal channel are presented in reference 57. <br />h. Stone Gradation. The gradation of stones in riprap revetment <br />affects the riprap's resistance to erosion. The stone should be reason- <br />ably well graded throughout the in-place layer thickness. Specifications <br />should provide for two limiting gradation curves, and any stone gradation, <br />as determined from a field test sample, that lies within these Hmits should <br />be acceptable. The gradation limits should not be so restrictive that stone <br />pr<>duction costs would be excessive. The choice of limits also depends on <br />the underlying 'filter requirements if a graded stone filter is used. Cri- <br />teria for filter requirements are given in_EM 1110- 2-1901. The follow- <br />ing criteria provide guidelines fo.r establishing gradation limits. <br />(1) The lower limit of W 50 stone should not be less than the weight of <br />( .;one required to withstand the design shear forces as determined by the <br />procedure given in paragraph g above. <br />(2) The upper limit of W 50 stone should not exceed that weight which <br />can be obtained economically from the quarry or that size which will satisfy <br />layer thickness requirements specified in paragraph i below. <br />(3) The lower limit of W100 stone should not be less than two times <br />the lower limit of W 50 stone. <br />(4) The upper limit of W 100 stone s.hould not exceed: five times the <br />lower limit of W 50 stone, that size which can be obtained economically <br />from the quarry, or that size which will satisfy layer thickness require- <br />ments specified in paragraph i below. <br />(5) The lower limit of W 15 stone should not be less than one- <br />i sixteenth the upper limit of W 100 stone. <br />(6) The upper limit of W 15 stone should be less than the upper <br />limit of W 50 stone as required to satisfy criteria for graded stone <br /> <br />j <br />, <br />, <br />j <br />1 <br /> <br />I <br /> <br />14h(6) <br /> <br />42 <br /> <br />'"~,,,/ <br /> <br /> <br />_"'I:t?")i(;.:~ _, ,,,; <br />