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<br />DEPARTMENT OF mE ARMY
<br />Office of the Chief of Engineers
<br />,Washington, D.C. 20314
<br />
<br />ETL 1110-2-120
<br />
<br />ENGCW~EH
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<br />Engineer Technical
<br />Letter No. 1110-2-120
<br />
<br />14 May 1971
<br />
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<br />ENGINEERING AND DESIGN
<br />Additional Guidance for Riprap Channel Protection
<br />
<br />1. Purpose. The purpose of this ETL is to discuss detailed factors
<br />which must be considered in the application of criteria presented in
<br />paragraph 14 of EM 1110-2-1601, "Hydraulic Design of Flood Control
<br />Channels", to the design of graded stone riprap channel protection,
<br />present additional hydraulic design guidance, .and suggest a coordinated
<br />office design procedure which should be adopted. , ..,
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<br />2. Applicability; This letter is applicable. to' all divisions and
<br />districts having the responsibility for the design and co~struction,~f
<br />Civil Works projects.,.,,:,: ", .,,;,.l;Wi',iri>'p."L
<br />
<br />,3. Discussion. . "_ -',~,:~!;..~:~J~:;I~<g;'W~~I"
<br />
<br />. a. Riprap Physical Characteristics - Design Phase. The stone.,,"
<br />i shape *(paragraph l4c), gradation limits (paragraph 14h) . and layeJ;' 7,
<br />, thickness (paragraph l4i) are riprap material parameters for, which '..
<br />equations (33) and (34), using 0.040 for coefficient "a" indicate the
<br />ability of the riprap to resist boundary shear. .The criteria are
<br />,sufficiently broad to encompass the usual riprap material produced, ..
<br />""from many acceptable quarries. A grizzly or similar type processing
<br />operation may be required to obtain acceptable riprap material from
<br />some' quarries. Riprap material. which fails to meet the criteria. for
<br />gradation limits. or stone shape is not capable of resisting the same
<br />, amount of shear as indicated by the value of 0.04 for "a" in equation
<br />'. (33). As sufficient information is not available on which to base
<br />.. an adjustment of "a" for such materia1, sufficient samples should be
<br />tested during the design stage to determine its strength, gradation, ~~.
<br />and stone-shape limits within which materlal can be produced without,,,~,
<br />undue waste. Sample .test installations should be made in varying "W,. "
<br />layer thicknesses to establish the layer thickness required. to produce . :J(;~~
<br />an acceptable protective blanket, giving consideration to the following: _-~~f
<br />
<br />. ..'-d)d'ul ~~~ie'~;";ho~id'~~"cont~ined -reas~nablY w~il ~~[1hIt~~;::!r..,:;~,;x~.: '~i::
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<br />1a thO kn . ...-'-. - .. f -"~t<~;;,' :>:,,':,;-.-.::-:.- ,j!~.~,<t;~;-,'...-_,~_~ <'...\-~ ~~.-
<br />yer 1C ess~ ,- ___^:',~ --':....,''7 .~.~..{.l ~.,'...' - \;,_:~,'_, --:.~,~~..,c~~".--.
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<br />(2) , Surface. .irr_egulari t!es should be minimal ." ;'".~ . ... "" ..
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<br />*Subparagraphs and equations indicated in the text, unless otherwise
<br />
<br />noted, are found in paragraph 14, EM 11l0~2-160l. .
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