FLH PDDM Chapter 9 - Eastern Federal Lands Highway Division

9.4.C. Earthwork Design. (continued)3. Classification of Roadway Excavation. Classification of roadway excavation for design purposes includesthe following types:Common material. Common material is largely earth or earth with detached boulders less than 0.5 cubicmeter.Rippable rock. Rippable rock refers to material ready for excavating after it is loosened by a ripper.Solid rock. Solid rock includes hard rock in place, ledge rock, and boulders requiring drilling and blastingequipment for removal. Any blasting work will be performed according to the rock blasting sectionspecifications.In addition to the excavation for the construction of roadways, there may be excavation for drainage ditches,culverts, bridges, and grade separation structures. Still another type of excavation includes dredging operationsfor hydraulic fills.Using data furnished by the geotechnical staff, the designer shall check the characteristics of the material tobe excavated or placed in embankments. The excavation used for embankments will range from rock to earthand have shrink/swell factors assigned for design purposes.4. Shrink and Swell Factors. Roadway excavation, however classified, is commonly but not alwaysmeasured in the original, undisturbed position. The specifications must carefully state the place and methodof measurement because almost all materials change volume in their movement from cut to fill.Excavated earth will expand beyond its original volume in the transporting vehicle but will shrink below theexcavated volume when compacted into the fill. To illustrate, 1 cubic meter of earth in the cut may use 1.25cubic meters of space in the transporting vehicle, and finally occupy only 0.65 to 0.85 cubic meters in theembankment. This, of course, depends on its original density and the compactive effort applied. Thisdifference between the original volume in a cut and the final volume in a fill is the shrink.Excavated rock placed in a fill occupies a larger volume. This change in volume is the swell. When the voidsin the rock embankment become filled with earth or other fine material, the volume in the fill will just aboutequal the combined volumes in the two source locations.For light soil excavation and for fills constructed on swampy ground subject to settlement, the shrink mayrange from 20 to 40 percent or even greater. For moderate soil excavation, the shrink ranges from 10 to25 percent. For heavy soil excavation with deep cuts and fills, expect a range of about 15 percent shrink to5 percent swell. Shrink generally includes the slight waste in transporting material from cut to fill and the lossfor material which escapes beyond the toe of slopes.A swell of 5 to 25 percent is anticipated in rock excavation depending upon the proportion of solid rock andupon the size of the rock placed in the fill.When available, the design should incorporate actual field shrink and swell factors for like material used onadjoining projects.9 - 72