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<br />. <br /> <br />I <br /> <br />t <br />~ <br /> <br />. <br />I <br />l <br />I <br />, <br />, <br />, <br />, <br />~ <br />~ <br />I <br />I <br /> <br />. <br /> <br />. <br /> <br />~ <br />, <br />f <br />, <br />, <br />I <br />, <br />f <br /> <br />, <br />I <br />I <br />~ <br />I <br />I <br />I <br />I <br /> <br />'" <br /> <br />. <br /> <br />A filter layer under all riprap is essential (1) unless the bank <br />material meets the fll ter requirements. (See section 2.7.) <br /> <br />(1) Dumped riprap is graded stOlle dumped on a prepared slope in <br />such a manner that segregation will not take place. Dumped stone <br />riprap is the most :flexible of the types considered here and will <br />adjust itself to uneven bank settlement. In most areas dumped <br />stone is the least costly type. <br /> <br />(2) Hand-placed riprap is stone laid carefully by band or by der- <br />rick fo11owiDg a more or less definite pattern with the voids <br />between the larger stone filled with smaller stone and the surface <br />kept relatively even. The resulting protectioo approaches good dry <br />rubble in quality and appearance, but this type of riprap is rigid <br />and lacks the strength necessary to bridge even minor movellBnt of <br />the surface which it protects. <br /> <br />(3) Wire-enclosed riprap is stone placed in wire baskets or in <br />wire covered mats. Wire-enclosed riprap is generally used because <br />rock at suitable size is not available. This riprap is effective <br />until the wire enclosure fails. <br /> <br />(4) Grouted riprap is riprap with the interstices filled with port- <br />land cement mortar. The use of grouted riprap is seldom justifiable <br />when stone of suitable size is available. <br /> <br />(5) Concrete riprap in bags is concrete in cement sacks or suitable <br />burlap bags that are band placed in contact with adjacent bags. <br /> <br />(6) Concrete-slab riprap is plain or reinforced concrete slabs <br />poured or placed on the surface to be protected. The slabs poured <br />or placed on the surface to be protected. The slabs are not coo- <br />nected to each other. <br /> <br />II - DEBIG. <br /> <br />2.1 - Design at Dumped-Stone Riprap <br /> <br />The resistance of dumped stone to displacement by moving water <br />depends upon: <br />(1) Weight, size, shape, and composition of the individual stones <br />(2) The gradation of the stone <br />(3) The depth at water over the stone blanket <br />(4) The steepness and stability of the protected slope <br />(5) The stability and effectiveness of the filter blanket on which <br />the stone is placed. <br /> <br />11-3 <br />