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<br />59 <br /> <br />--!- <br /> <br />Soil testing of a proposed fill area should be performhd to establish bearing capacity of the foun- <br />dation soil and requirement for the fill soil. Potential fettlement should also be investigated with <br />soil tests. The best preventive tool against excessive :settlement is to ensure proper compaction <br />when placing the fill material. <br /> <br />Soils with the best characteristics for U5e in a structulre-supporting fill are well-graded sands and <br />gravels, which may contain a small percentage of finelclay material. Undesirable soils include the <br />highly plastic, swelling clays and also soils which are ~ifficult to compact - cohesion less silts and <br />very fine uniform sand, With proper methods, most inorganic soils will create an acceptable <br />fill. <br /> <br />After a suitable fill material has been identified, ~Iacement should be done at or near the <br />optimum moisture content for compaction. Using a~propriate compaction equipment. such as <br />pneumatic or sheepfoot rollers, the fill should be plac~d in layers no greater than13 inches thick. <br />Compaction 3 to 95 percent of the Standard Proctor ~ensity (defined below) in accordance with <br />standard engineering practice will suffice for most blJilding applications, <br />, <br /> <br />Standard Proctor(ASTM 0 698-78, AASHTO T - 180-74):1 Twenty five blows of a 5.5 Ib hammer falling <br />, <br />12 inches on each of three equal layers in a four inch df4meter 1/30 ft3 cylinder.' The effort is 12,400 <br />ft-lb/ft3, which is comparable to light rollers or very thorough tamping in thin layers. <br /> <br />" If the soil contains many particles larger than a No, 4 sfrve, a six-inch diameter cylinder of the same <br />height is used and the blows increased to 55 per laYFr, <br /> <br />Figure 7.1 shows the geometry for a typical raised-on,fill construction, Some very general recom. <br />mendations are given here <br /> <br />1 ,Local code requirements may vary, but the lini"hed' floor elevation should be a minimum one <br />foot above the BFE. <br /> <br />2.Riprap should be placed on the slopes if the stream vhlocity will exceed three fps. General riprap <br />requirements call for 12" to 24" mean diameter riprap! with a unit weight from 150 to165 pounds <br />per cubic foot, placed in a layer at least 1.75 times lhe mean diameter (Referc,nce No, 44), <br /> <br />3.The minimum horizontal distance that the fill should f"tend beyond the exterior of the structure <br />should be 15 feet. There is also an OSHA requiremeint for emergency exits. <br /> <br />4,Slope stability calculations are best done by a prc,fessional engineer with the specific 50il <br />parameters, Recommended fill slopes for riprap lined !embankments are 2.5,1 to 3:1. For vegeta- <br />tion lined embankments the recommended fill slope! is a maximum of 4,1. <br /> <br /> <br />'0 <br /> <br />DESIGN FLOOD <br />ELEV 99' <br /> <br />FREEBOARD I' <br /> <br />+--- <br /> <br />ELEV. 100' <br /> <br />RIPRAP IF VELOCITY IS <br />GREATER THAN 3 FT /Sec <br /> <br />FilL <br /> <br />MIN. TOE DEPTH 2' <br /> <br />GROUND <br /> <br />TOP 6"-12" OF TOPSOIL <br /> <br />FOR MOST SITUATIONS, ASSLJME A RIPRAP LAYER OF 1.75 TIMES THE MEAN DIAMETER STONE. <br /> <br />Figure 7.1, Geometry for raised-on"fill construction <br />