Laserfiche WebLink
<br />. <br /> <br />. <br /> <br />. <br /> <br />I <br />'. <br />~ <br /> <br />, <br />~ <br />I <br />I · <br />, <br /> <br />. <br /> <br />. <br /> <br />The gradation of the sand and the gravel is satisfactory; if <br />adequate placing methods are to be used, two minimum thickness layers <br />(4 or 5 inches) can be used, one of sand and one ot graveL <br /> <br />For riprap other than dumped stone, the maximum size of openings <br />in the cover is used as the criterion. Then: <br /> <br />D85 of the filter ( p. 171.) <br />= 2 or more 7, .. <br />Maximum opening in cover - <br /> <br />When weep holes are used in a solid cover, an inverted filter should be <br />used under the weep holes in addition to the filter blanket. <br /> <br />III - MATERIALS <br /> <br />Broken concrete may be substituted for stone when it meets the <br />requirements for stone. <br /> <br />3.1 - Dumped-Stone R1prap <br /> <br />Stone used for dumped riprap should be hard, durable, angular in <br />shape; resistant to weathering; tree trom overburden, spoil, shale, and <br />organic material; and should meet the gradation requirements for the class <br />specified. 5either breadth nor thickness ot a single stone should be less <br />than one-third its length. Rounded stone or boulders are not acceptable. <br />Shale and stone with shale seams are not acceptable. The minimum weight <br />at the stone should be 155 pounds per cubic foot as c~ted by multip1:ying <br />the specific gravity (bulk-saturated-surface-dry basis, AASHO Test T 85J <br />times 62.3 pounds per cubic foot (18). <br /> <br />The sources from which the stone is to be obtained should be selected <br />well in advance of the time when the material will be required in the work. <br />The acceptability of the stone is determined by service records and/or by <br />suitable tests. If testing is required, suitable samples of stone should <br />be taken in the presence of the engineer in sufficient time for testing <br />before the placing of riprap is expected to begin. <br /> <br />In the absence of service records, resistance to disintegration from <br />environmental exposure is detel'lllined by the sulfate soundness test or by <br />the abrasion test in the Los Angeles machine. The freezing aDd thawing <br />test furnishes a useful guide in judging the soundness of stone subject to <br />weathering action, but it should not be used as an arbitrary basis for <br />rejection. In locations not subject to tree zing or where the stone is <br />exposed to salt water, the sultate soundness test (AASHO Test T 104 for <br />ledge rock using sodium sulphate) should be used. Stones should have a <br />loss not exceeding 10 percent with the sulfate test after five cycles. <br /> <br />11-19 <br />