In-Situ vs Loose Volume (and Compacted)
In-situ volume is the undisturbed material as it sits in the ground; loose volume is the same material after excavation, when voids are introduced and it bulks up; compacted volume is the same material after placement and rolling, which reduces voids below the in-situ state. This is why a survey, a haulage tally and a weighbridge can each report a different, correct number for the same earthworks job — they are measuring the same material in three different states. Here is how to keep them straight.
The same material, three volumes
In-situ volume — also called bank volume — is the material as it sits undisturbed in the ground. This is what a survey measures, because a survey measures the shape of the ground before and after.
Loose volume is the same material after excavation. Digging introduces voids, so it takes up more space. This is what a truck body holds and what a haulage tally counts.
Compacted volume is the same material after being placed and rolled. Compaction squeezes out more voids than the ground had originally, so it occupies less space than in situ.
One mass of rock or soil, three legitimately different volumes. A figure without its state is ambiguous, and most disputes are two people quoting different states at each other.
Bulking and shrinkage
The increase from in situ to loose is bulking, or swell. The decrease from in situ to compacted is shrinkage. Both are expressed as factors or percentages against the in-situ volume.
The ordering is consistent and worth knowing by feel: clean sand and gravel bulk the least, common earth more, clay more again, and blasted rock most of all — a broken rock pile can occupy substantially more space than the solid it came from, because the fragments cannot re-pack.
The actual figures are material properties, not constants. Published tables give indicative ranges and they are fine for a first estimate, but for anything contractual the factor has to come from testing the material on your site. Two clays from different pits do not behave the same, and moisture changes the answer.
Where the truck count goes wrong
Even with a correct bulking factor, a haulage tally is a rough instrument. Body volumes are nominal, loads are not consistently level, and heaped versus struck loads differ by a lot. Counting loads and multiplying by a nominal body volume compounds every one of those.
A weighbridge is much better because mass does not change with state. But mass only converts back to volume through a density, and density moves with moisture — the same truckload after rain weighs more and represents no extra material.
So: survey volume is the reliable measure of what left the ground. Truck counts are a cross-check, not a rebuttal.
Density, tonnage and money
For sold material the unit is usually mass, so volume gets converted with a density. That conversion is where quiet errors live: an in-situ density applied to a loose volume, or a dry density applied to wet material, both produce confidently wrong tonnages.
STREAM carries material, density and unit price alongside a stockpile or cut/fill result, so the volume, the tonnage and the value stay attached to the surfaces they came from instead of being recomputed by hand in a spreadsheet each month.
Keep the chain explicit: which volume state, which density, at what moisture. Any figure that cannot answer those three is not auditable.
The practical rules
Label every volume with its state. "12,400 m³ loose" is a fact; "12,400 m³" is an opinion.
Do earthwork balance in one state, normally in situ, and convert only at the end for haulage or payment.
Get the factors for your material from testing, and record them in the report next to the numbers they produced.
When survey and trucks disagree, check the state first, the density second, and the survey boundary third. In that order, you will find it almost every time.
Frequently asked questions
What is the difference between in-situ, loose, and compacted volume?
In-situ volume is the undisturbed bank volume of the ground; loose volume is the volume after excavation, when voids are introduced and the material bulks up; compacted volume is the volume after placement and rolling, which reduces voids below the original in-situ state (shrinkage).
Why do survey figures and truck counts disagree on an earthworks job?
Usually nobody made an error — the survey reports the in-situ number, the haulage tally reports the loose number, and the weighbridge reports mass, so all three are correctly measuring the same material while it's in three different states.
Why is a weighbridge more reliable than counting truck loads for volume?
Truck body volumes are nominal and loads are inconsistent (heaped versus struck loads vary), whereas a weighbridge measures mass, which does not change with the material's state, making it a more dependable check — though mass still converts back to volume through a density that moves with moisture.
What information should accompany a volume figure to make it auditable?
A usable figure must be able to answer three things: which volume state it is (in-situ, loose, or compacted), which density was used, and at what moisture condition — a number that can't answer those three isn't auditable.
Sources
Measure stockpile volume and tonnage in STREAM
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