Earthworks quantities: volume in the ground, volume in the truck, soil from a pile bore, and the swell factor
Calculating earthworks quantities starts with a point that is easy to miss: which volume you are talking about. The same soil takes up one volume in the ground, a larger volume in the body of a truck, and a smaller volume after it is compacted as fill. I have experience in quantity takeoff for excavations, basements and piles, from drawings, surveys and soil reports, and in my graduation project I also calculated the number of trucks and the soil stockpile on site.
Three volumes: natural, loose and compacted
Natural volume, also called in-place (bank) volume, is the volume of the soil as it is in the ground before excavation. Loose volume is the volume after excavation, in a heap or in a truck body: the soil breaks up, air gets into it and it takes up more space. Compacted volume is the volume after the soil is spread and compacted in layers, as fill.
On Israeli sites the ratio between the loose volume and the natural volume is called the swell factor (mekadem hatpakha). In design documents it also appears as "the increase factor of the excavated material", and some call it a swelling factor or a loosening factor. The names are not consistent, so it is worth writing explicitly what is meant: a number that multiplies the natural volume to give the volume for haulage. This is not the same thing as expansive clay, a soil that swells when it gets wet and shrinks when it dries. That phenomenon belongs to the soil report and the foundation design, not to the truck calculation.
| Soil type | Volume increase | Swell factor |
|---|---|---|
| Sand | 12% | 1.12 |
| Gravel | 12% | 1.12 |
| Ordinary earth | 25% | 1.25 |
| Clay | 40% | 1.40 |
| Rock after blasting | 65% | 1.65 |
Hence the rule of thumb I work with: times 1.3 for the truck calculation. It is a practical rounding between ordinary earth and clay, and on most residential sites it gives the right order of magnitude. In sand you can use less, and in heavy clay or rock you need more. The value for a particular project is set by the actual soil type, so it has to be checked against the soil report and with the geotechnical consultant and the structural engineer. On the soils of this country, see the page soil types in Israel.
How earthworks quantities go into the bill of quantities
In the methods of measurement of the General Specification for building works (Israel's inter-ministerial specification), in the earthworks chapter, the quantities of excavated material and of fill material are taken as equal to the quantities of soil before excavation. Losses in haulage and the difference between the theoretical calculation and reality do not go into the quantity. In plain words: the bill of quantities (BOQ) counts natural volume, and the bulking, loading and haulage are part of the rate. Whoever prices the work has to calculate for themselves how many trucks will go out.
The common mistake is to take the volume from the bill, divide it by the truck capacity, and get a number of trips that is about a third lower. In the bill itself, the calculation follows the existing ground levels shown on the drawings, by the method of average areas, without local bumps and hollows between the survey points. The general logic of the measurement rules is explained on the page methods of measurement.
Example: excavation for a basement, from cubic metres in the ground to a number of trucks
This is the most common example of calculating earthworks quantities on residential sites. A basement of 20 by 15 metres, 3.5 metres deep, with a working space of one metre on each side for the walls and the waterproofing. The calculation, for illustration:
| Step | Calculation | Result |
|---|---|---|
| Excavation footprint | 22 × 17 | 374 m² |
| Natural volume | 374 × 3.5 | 1,309 m³ |
| Loose volume | 1,309 × 1.3 | about 1,702 m³ |
| Trips of 15 m³ | 1,702 ÷ 15 | 114 |
| The same calculation without the factor | 1,309 ÷ 15 | 88 |
The gap is 26 trips, almost a third. In my graduation project I calculated with an 18 m³ truck, and it came to 207 trips in the first stage and 126 in the second. The backfill starts here too: the working space around the basement is about 1,309 minus 1,050, that is 259 m³, and if you want to fill it with soil from the excavation you need to keep about 340 m³ of loose soil on site, before compaction.
A heap like that needs space. In the graduation project I planned a stockpile with a natural slope of about 1 to 2.2, one vertical to 2.2 horizontal. The diagram in short: a stockpile 3 metres high → times 2.2 → 6.6 horizontal metres on each side → a base 13.2 metres wider than the top. If you do not plan this area, you find out in the middle of the excavation that there is nowhere to put the soil.
How much soil comes out of a pile bore
The formula is simple: the area of the circle times the depth, and the area of the circle is pi times the radius squared. A pile 60 cm in diameter: 3.1416 times 0.3 squared, that is 0.283 m², and at a depth of 12 metres it gives 3.39 m³ in the ground. Loose, times 1.3, that is about 4.4 m³. Forty such piles produce about 136 m³ natural, about 176 m³ loose, and roughly 12 trips of 15 m³.
| Pile diameter | m³ natural per metre | m³ loose per metre, times 1.3 |
|---|---|---|
| 50 cm | 0.196 | 0.25 |
| 60 cm | 0.283 | 0.37 |
| 80 cm | 0.503 | 0.65 |
| 100 cm | 0.785 | 1.02 |
Roughly the same volume is also the concrete volume of the pile, and in soft soil the actual consumption can be higher. How piles and shoring go into the bill is explained on the page piles and shoring in a BOQ.
The rule in one line: natural volume in the bill of quantities, loose volume in the trucks, and compacted volume in the fill. Mixing them up means an error of tens of per cent, and it only shows when the trucks are already on site.
In earthworks a quantity surveyor also checks the swell factor in the contract, because it changes the number of trucks and the cost of removal.
Frequently asked questions
What is the difference between the swell factor and expansive clay?
The swell factor describes the increase in volume after excavation and is used to calculate haulage. Expansive clay is a property of the soil in place, which affects the foundations and the floor slabs, and it appears in the soil report.
Why times 1.3 in particular?
Because in ordinary earth the increase is about a quarter, and in clay close to 40%. The number 1.3 is a practical rounding that suits most residential sites. In heavy clay, clean sand or rock, the calculation follows the actual soil.
Is backfill measured separately?
Usually yes, as an item of its own, and sometimes it is included in the excavation rate. What matters is that the bill says so explicitly. How the soil report is turned into items is explained on the page soil report and BOQ.
Who calculates the earthworks quantities for a project?
A quantity surveyor for construction projects, from the excavation drawings, the survey and the soil report. For basements and underground car parks, see also the page BOQ for a basement and car park.
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Contact me for a quote* Created with AI for marketing, for illustration only. Not reviewed by Yaakov Avital and not professional advice. Every project must be checked on its own by a professional quantity surveyor and an engineer.