Field bulk density and dry density by the core cutter method (IS 2720 Part 29).
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In-situ Density Calculator (Core Cutter): Free Online Tool
The core cutter method measures the in-situ density of fine-grained soil. A steel cylinder of known volume is driven into the ground, removed with its soil, and weighed. Dividing the soil mass by the cutter volume gives the bulk density, and using the water content of the same soil gives the dry density.
Site engineers, quality control technicians and students use it to check compaction of embankments, subgrade, backfill and earth dams. The result is compared with the maximum dry density from a laboratory compaction test to find how well the soil has been compacted. This calculator follows IS 2720 Part 29. It calculates the cutter volume, soil mass, bulk and dry density, unit weights in kN/m3 and, if you enter the maximum dry density, the degree of compaction.
When to use this calculator
Use this calculator at the site or in the lab after taking a core cutter sample from a compacted layer of clay, silt or other cohesive soil. It is suited to checking the field density of embankment layers, road subgrade and trench backfill. Enter the cutter inner diameter and height in cm, the mass of the empty cutter and of the cutter with soil in grams, and the water content from an oven-dry test. The defaults are a 10 cm by 12.5 cm cutter. Add the maximum dry density to see the compaction percentage.
How to use the In-situ Density Calculator (Core Cutter)
- Open the calculator above on your phone, tablet or computer. Nothing needs to be installed and no sign-up is required.
- Enter your values in the input boxes: Cutter inner diameter (cm), Cutter height (cm), Mass of empty cutter (g), Mass of cutter + soil (g), Water content of soil (%), Max dry density (g/cm³, optional). The boxes already hold sample values, so overwrite them with your own.
- Press Calculate. The result appears straight away under the button.
- Change any value and press Calculate again to compare options. Press Reset to go back to the sample values.
- Check the result against your drawings, project specification and local code before you order material or approve work.
How the calculation works
The cutter volume is calculated from the inner diameter and height, and the mass of wet soil is the mass of cutter plus soil minus the empty cutter. Bulk density is wet soil mass divided by cutter volume, in g/cm3. Dry density is the bulk density divided by (1 + w), where w is the water content as a fraction. The calculator also gives unit weights in kN/m3. If you enter a maximum dry density greater than zero, it computes the degree of compaction as dry density divided by maximum dry density, as a percentage. Leave it at 0 to skip this check. The water content must come from a separate oven-dry test on the same soil.
Worked example
When you open the page the calculator is filled with sample values. Pressing Calculate with those values gives the result below, which you can use to check that you are reading the output correctly.
| Cutter and soil | |
|---|---|
| Cutter volume (cm³) | 981.7 |
| Mass of wet soil (g) | 1,620.0 |
| Density | |
| Bulk density (g/cm³) | 1.650 |
| Bulk unit weight (kN/m³) | 16.18 |
| Dry density (g/cm³) | 1.473 |
| Dry unit weight (kN/m³) | 14.45 |
| Compaction check | |
| Degree of compaction (dry density / max dry density) | 90.9 % |
Tips and common mistakes
- Take the water content from soil taken at the same spot and time as the core, not from a different location or day.
- Weigh the cutter with soil immediately after trimming, and seal the sample, so no moisture is lost before the mass is recorded.
- Trim the soil flush with both ends of the cutter. Voids or extra soil change the effective volume and the density you calculate.
- Use the inner diameter of the cutter, not the outer diameter, when entering the dimensions, since the volume depends on the square of diameter.
- Enter the maximum dry density from the laboratory compaction test in g/cm3. Do not mix it with kN/m3 values.
Frequently asked questions
What is the difference between bulk density and dry density?
Bulk density includes the water in the soil. Dry density is the mass of solids per unit volume, found by dividing bulk density by (1 + w). Compaction is judged on dry density because water content varies.
What is the degree of compaction?
It is the field dry density divided by the maximum dry density from the laboratory, shown as a percentage. For the default example, 1.473 divided by 1.62 gives 90.9 %. Check your specification for the required value.
Can I use the core cutter in gravelly or sandy soil?
The method suits fine-grained soils that the cutter can be driven into without loss of material. Coarse, gravelly or very hard soils are not suitable, and another method should be used.
Why is a separate water content needed?
The core gives total mass, which includes water. To find the dry density the water content must be known, so take a sample of the same soil and measure it by the oven-dry method.
Which units does the calculator use?
Enter dimensions in cm, masses in g and water content in per cent. Densities are shown in g/cm3 and unit weights in kN/m3. The maximum dry density is also entered in g/cm3.
Important note
This tool gives estimates for planning, study and quick checks. It does not replace design by a qualified engineer, site-specific testing, or the requirements of your project specification and local building code. Always confirm final quantities, test results and acceptance limits with the responsible engineer before using them for construction or payment.
