1. Definition:
A bulk density of a soil sample is defined as a mass per unit volume. The bulk density is denoted by ρm and has a unit of g/cm³ or Mg/m³.
2. Calculation:
where:
| ρm | bulk density (g/cm³ or Mg/m³) |
| m | mass of a soil sample (g or Mg) |
| V | volume of that soil sample (cm³ or m³) |
» In order to know a mass m of a soil sample then... that sample should be placed on the scale.
» In order to know a volume V of that soil sample then... the procedure is a little complicated:
• If the soil sample has a regular shape, for instance, cube or cylinder... : the volume of that soil sample could be calculated based on their dimensions.
• If the soil sample has an irregular shape: its volume can be determined indirectly using Archimedes' principle.
3. Determination of in-situ density:
One of the common methods for determination of in-situ density is to determine the volume V of a hole on the ground and the mass m of soils taken from that hole.
Nowadays, there are several methods for determination of volumes.
» The drive-cylinder method is a simple one but taking more effort. The mass m is the mass of soils inside the cylinder. The volume V is exactly the volume of cylinder.
» Sand-replacement and rubber-balloon methods use the same principle: the volume of a hole on the ground is determined indirectly by a density of another material: standard sand particles (for sand-replacement method) and water (for rubber-balloon method).
» Both nuclear gauge and electrical density gauge methods do not request to prepare a hole for measuring the volume. The water content and bulk density of the ground could be interpolated using a predefined correlation between water content/density with nuclear transmission or electrical properites.
The common apparatuses for those methods are displayed below.
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| Drive-cylinder method |
Sand-replacement method |
Rubber Balloon method |
Nuclear gauge method |
Electrical density gauge method |
4. Reference standards:
a) ASTM D7263 : Standard Test Methods for Laboratory Determination of Density (Unit Weight) of Soil Specimens
b) ASTM D2937 : Standard Test Method for Density of Soil in Place by the Drive-Cylinder Method
c) ASTM D1556 : Standard Test Method for Density and Unit Weight of Soil in Place by the Sand-Cone Method
d) ASTM D2167 : Standard Test Method for Density and Unit Weight of Soil in Place by the Rubber Balloon Method
e) ASTM D5195 : Standard Test Method for Density of Soil and Rock In-Place at Depths Below Surface by Nuclear Methods
f) ASTM D7698 : Standard Test Method for In-Place Estimation of Density and Water Content of Soil and Aggregate by Correlation with Complex Impedance Method