OpenSpecEngineering

Converts an earthwork volume between its three states: bank (in place, before digging), loose (dug and in the truck) and compacted (placed and rolled in a fill). Estimators and site engineers use it to find how many truckloads a cut produces, or how much ground to dig to build an embankment of a given size.

Equations

V_L = V_B·(1 + S_w)     V_C = V_B·(1 − S_h)     LF = V_B/V_L = 1/(1 + S_w)

V_B, V_L and V_C are the bank, loose and compacted volumes. S_w is the swell, the fraction by which a bank volume grows when it is dug. S_h is the shrinkage, the fraction by which a bank volume shrinks once it is compacted in the fill. LF is the load factor [1], [2]. Choose Volume Basis to say which state the known volume is in. The page converts it to bank volume first and then to the other two states.

Inputs

• Choosing a Material fills in the swell from the Caterpillar load factor for that soil [2], [3]. Pick Custom, or type over the swell, to use your own value, for example from a test pit.
• Shrinkage has no table here, because it depends on how hard the fill is compacted. Take it from the compaction spec, a lab compaction test or past jobs [1]. Blasted rock often ends up larger in the fill than in place, a negative shrinkage that this page does not accept.

Limits and common mistakes

• Swell and shrinkage are both measured from bank volume. Don’t apply a shrinkage to a loose volume.
• A load factor of 0.80 means a swell of 25 %, not 20 %.
• Truck and bucket capacities are loose volumes, while survey quantities from cross-sections are bank or compacted volumes.
• The table values are averages. Moisture, gradation and handling change them, so check them on site for large jobs.

Worked example

An embankment needs 2,500 m³ of compacted fill from a borrow pit of loam. The compaction spec is expected to give a shrinkage of 12 %. How much must be dug, and how much will the trucks carry?

1. Enter Known Volume 2500 and choose Volume Basis Compacted (placed).
2. Choose Material Earth, loam — load factor 0.81. The swell fills in as 23.4567901235 %.
3. Enter Shrinkage 12 and press Solve. The Solution shows: Load factor (bank/loose): 0.81
   Shrinkage factor (compacted/bank): 0.88
   Bank volume: 2,840.91 m³
   Loose volume: 3,507.3 m³
   Compacted volume: 2,500 m³
   Bank volume: 3,715.77 yd³
   Loose volume: 4,587.37 yd³

Check by hand: bank = 2500/0.88 = 2,841 m³, and loose = 2841/0.81 = 3,507 m³. At 10 m³ of loose material a load, that is about 351 truckloads.