FLH PDDM Chapter 9 - Eastern Federal Lands Highway Division

9.4.C. Earthwork Design. (continued)The shrink factor is determined as follows:Shrink Factor =11 % shrinkage100Thus, if the percent of shrink is 25 percent, the shrink factor would be:112510011.250.8The swell factor for rock excavation is determined as follows:Swell Factor =1% swell100Thus, if the percent of swell is 25 percent, the swell factor would be the following:1251001.25See Table 6-12 in Chapter 6 for additional information on shrink/swell factors used for commonly specifiedmaterials.The shrink/swell factors are applied to the excavation quantities to arrive at the adjusted quantities.Settlement results in shrinkage, but one is not directly proportional to the other. Do not confuse shrink withsubsidence. Subsidence is settlement of the entire embankment due to unstable foundation conditions suchas placing heavy fill on swampy soil.5. Design Cut and Fill Slopes. The design of cut and fill slopes depends upon the characteristics of thematerial. The designer should refer to the geotechnical report for recommended slope ratios. (See Section9.4.A.)6. Slides. When the geotechnical report identifies potential areas for slides, the earthwork excavationquantities may require adjustment to cover potential slide removal. Provisions to dispose of excess slidematerial are necessary.7. Balancing Earthwork. The earthwork is balanced when the volume of excavation (with the appropriateallowances made for shrink and swell) equals the volume of embankment. The designer shall consider thequantity of subexcavation removed and disposed of and the quantity of topsoil reserved for slopes in thebalance quantities.It frequently happens that the material from the adjacent cuts is not sufficient to make the intervening fill. Inthis case, material is borrowed from outside the construction limits.When there is an excess of excavated material, it may be necessary to dispose of the material. Instead of longhauls, it may be more economical to dispose of the material by widening shoulders or placing the material indisposal areas than to pay hauling costs.9 - 73