Expansion and Compaction
Updated December 15, 2021
This article applies to:
- RoadEng Civil
- RoadEng Forestry
Expansion and compaction is critical for calculating mass haul and estimating end haul. Even though the concept is simple, expansion and compaction can be confusing; especially when alternate reporting of cut and fill volumes is considered.
Expansion and compaction is usually reported in one of the following three styles:
Bank C Volume: (most common) In this system, cut and fill are reported as the equivalent volumes they would occupy in the natural state (in the bank or in situ). The reported cut volume is unmodified from the volume calculated in the road cross section.
Loose (trucked) Volume: In this system, cut and fill are reported as the equivalent volumes they would occupy in a loose state. Both cut and fill volumes are modified (swelled) from the volume calculated in the road cross section.
Final (placed) Volume: (not often used) In this system, cut and fill are reported as the volume calculated in the road cross section.
In this section we will provide an example that shows differences between these three reporting systems.
Please download the associated tutorial files here: Expansion and Compaction.zip
It was determined through testing that 1.0 m3 of in situ solid rock swells when blasted to 1.5m3 (loose), and when placed as fill, it settles to a final volume of 1.4m3. From this information we can make Table.
Table – List of cut and fill expansion factors for solid rock.
1. From the menu File Button | Open File, select expand.dsn. Your screen should look like Figure.
Figure – Expand.dsn
Notice, in the Data Window and the Profile Sub-Window that the cut and fill volumes are equal, and hence, no mass haul.
2. From Home tab | Configurations group | Ground Types button. Ground Types, select the Ground type named Solid Rock, as shown in figure below.
Figure – Ground Types Editor dialog box
Notice that the Cut/Fill Expansion Factors, in Figure, are both 1.0; we are currently using the Final (Placed) system. Also notice that there is no excess or deficit volume, as you can see in the Data Window of Figure.
3. Change the Cut/Fill Expansion Factors for Solid Rock to the ones shown in the Bank (in situ) row of Table 1.0 (i.e. 1.0 Cut and 0.714 Fill). Press OK. Respond OK to the Recalculate road alignment prompt.
Notice that the reported Fill V. and Mass H. have changed. Only 6.4 m3 of the 9.0m3 of bank volume is used, because this expands to the 9.0 m3 required for fill. The quantity left over at the end of the three segments, 7.7 m3, indicates that we cut this much extra solid rock, but the left over loose material in our truck will be larger than this amount (swelled).
4. From the menu Home tab | Configurations group | Ground Types button, select SR Solid Rock and change the Cut/Fill Expansion Factors to 1.5 for Cut and 1.07 for Fill, as shown in Table 1.0 for Loose (trucked). Press OK. Respond OK to the Recalculate road alignment prompt.
Notice that the reported volumes in the Data Window have changed, again. Since reporting is now based on loose material, the volumes are larger. The total volume left over is now 11.6 m3; this should accurately reflect the quantity of loose material trucked away.
If this little segment of road were actually built in solid rock there really would be material left over. Both the Bank and Loose methods are reporting accurate volumes (Bank tells how much digging or blasting you will do while Loose tells how much trucking you will do). The Final method however is telling you only the placed volumes; the Mass Haul of zero is incorrect (Mass Haul = cut volume - fill volume so cut and fill must be in the same units).
NOTE: Correct expansion and compaction factors should always be determined either through testing or from local soils information for your geographic location; otherwise your reported volumes will not be accurate.
NOTE: Even larger volume errors (as well as slope stake position errors) can be introduced if the cut and fill angles of your materials are inaccurate. Make sure all the engineering properties in your Ground Type Table reflect real materials in your geographic location.
5. File button | Close. Do not save changes.