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<br />Filter Bedding <br /> <br />The Contractor shall use porous, free-draining material, consisting of <br />sand, gravel, crushed stone or othel- approved free-draining material. <br />On-site materials shall be used if available when approved by the <br />Engineer. Imported materials shall be used if available when approved <br />by the Engineer. Imported materlals shall be used if no on-site <br />materials are available. All mater'ials shall meet the following <br />gradation requirements: <br /> <br />U.S. Standard <br />SeivE'=---- <br /> <br />Percent by ~~ight Passing Square Mesh Sieves <br />T:tBe II <br /> <br />90 - 100 <br /> <br />3" <br />1-1/2" <br />3/4" <br />3/8" <br />#4 <br />#16 <br />#50 <br />#100 <br />#200 <br /> <br />20 - 90 <br /> <br />o - 20 <br /> <br />0-3 <br /> <br />Execution <br /> <br />Rip ra p <br /> <br />Excavate for placement of rock riprap lining as ind'icated by the <br />1 ines and grades on the plans. Renove all soft, yielding material; <br />replace with suitable on-site material; compact to smooth firm <br />surface. Place filter beddinq material. Machine-place stones into <br />position following details indicated. Arrange as necessary by use <br />of gradall or multi-prong grapple device or hand to interlock and <br />form a substantial bond. Dumping and/or backhoe placement alone <br />is not sufficient to to ensure proper interlocked pl acement. <br />Basic procedure will result in materials that are d50 and larger <br />flush to the top surface with faces and shapes matched to minimize <br />voids. Surface grades will be a plane or as indicated, but <br />projections above or depress;ons under the average surface plane <br />more than 20% less of the rock layer thickness will not be allowed. <br />The average surface plane is degined as the plane where 50% of the <br />tops of rocks would contact. Voids will be filled with a well <br />graded mixture of the remaining material that is securely locked <br />between the larger stone. !tis essential that the material <br />between stones not beloose or E,a,;ily displaced by flow, The <br />remaining stone will also be used to provide a subgrade that will <br />arrive at a proper grade for the surface stone. The stone will be <br />consolidated by the bucket of backhoe or other means that will <br />cause interlocking of the materia'l. The stream side of the riprap <br />is to be uniform and free form bulges, humps, or cavaties. All <br />rock is to be placed in a dewatered condition beginning at the toe <br />of the slope or other lowest point. <br />