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<br /> <br />I <br />, <br /> <br />c <br /> <br />. <br /> <br />< <br /> <br />\._->~.,. <br /> <br />~-.--~--______._ _-0"__'__..- <br /> <br /> <br />EM 1110-2-1601 <br />1 July 70 <br /> <br />I.~ <br /> <br />plate 30 presents relations between spherical diameter and stone weight for <br />,everal values of specific weight. Design procedures for determining the <br />,tone weight required to resist the erosive forces of channel flow are pre- <br />eented in g below. <br />e. Channel Side Slopes. The stability of riprap bank revetment is af- <br />fected by the steepness of channel side slopes. Side slopes on which stone is <br />placed by machine or dumped should not be steeper than 1 on 2. Side slopes <br />for hand-placed riprap should not be steeper than 1 on 1.5, except in special <br />cases where it may be economical to use larger stone keyed well into the <br />bank. The size of stone required fo resist the erosive forces of channel <br />flow increases with the steepness of side slopes since the stabilizing grav- <br />itational,force component decreases. The design procedure for deter- <br />mining the effect of channel side slopes on stone size is presented in g <br />below. <br />f. Channel Roughness, Shape, AliJ;!:nment, and Invert Slope., As bound- <br />ary shear forces depend on channel roughness, shape, alignment, and invert <br />slope, these factors must be considered in determining the size of stone re- <br />quired for riprap revetment. In general, riprap size requirements may be <br />; reduced by increased channel roughness from the stone, adoption ofa broad <br />shallow channel with gradual alignment changes, and reduction of the invert <br />slope. The use of smaller stone reduces the cost of rip rap revetment but <br />other channel costs are increased. Comparative cost estimates should be <br />made for several alternative channel plans to determine the most economical <br />and practical combination of channel factors and stone size. <br />i g. Design Criteria for Stone Weight. (1) General. Riprap protection <br />I <br />lfor a flood control channel is subjected to hydrodynamic drag and lift forces <br />~hat tend to erode the revetment and reduce its stability. The drag and lift <br />~orces, which are created by flow velocities, are proportional to the iocal <br />boundary shear. Forces resisting motion are the submerged weight of the <br />/ltone and any downward force component caused by contact with other stones <br />In the re.vetment. The stability of the riprap revetment, then, depends upon <br /> <br />39 14g(1) <br /> <br />~, <br /> <br />~ <br /> <br />