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3.4 GEOTFJLTI6E FABRIC <br />Depending on the porosity of the finished rockfill, it may be necessary <br />to place geotextile filter fabric between the rockfill material and the <br />subbase material to prevent migration of subbase fines downward into <br />the rockfill material. We recommend using Mirifi filter fabric or a <br />suitable equivalent. If the rockfill material has sufficient fines to <br />prevent migration, filter fabric may be omitted on the approval of a <br />representative of our firm. <br />3.5 SUBBASE <br />Pit-run gravel to be used as subbase shall be placed to a minimum <br />compacted depth of 9" and conform to Class 2 State Highway <br />Standards 1981 Edition with a maximum of 6" rock. The largest stone <br />shall not be more than 2/3 of the subbase depth if a compacted thick- <br />ness greater than 9" is used. <br /> <br />3.6 BASE COURSE <br />A crushed aggregate base course shall be placed on the subbase course <br />to a compacted minimum depth of 4" to meet a class 6 standard as per <br />the State Highway Standards 1981 Edition. Where no paved surface <br />course is required, the base course shall be constructed to be the surface <br />course. All material shall be of sound aggregate particles and shall be <br />free of organic matter. <br />• 5 <br />