Relative Density of Soil

Relative density of soil, abbreviated as \(D_r\), also called density index or degree of compaction, a dimensionless number, is a measure of how densely packed or compacted a soil sample is compared to its maximum achievable density.  It is an important parameter in geotechnical engineering and is used to assess the engineering properties and behavior of soils.

Relative density is typically expressed as a percentage and can range from 0% (loose, uncompacted soil) to 100% (fully compacted soil).  The value is obtained by comparing the actual density of a soil sample to the maximum possible density it can achieve under the same conditions.  In other words, it indicates how much the soil has been compacted relative to its natural or loose state.

Here, "dry density of compacted soil" is the density of the soil after it has been compacted through some construction or compaction process, and "maximum dry density" is the highest achievable density for that specific soil under the given compaction conditions.

Engineers use relative density to assess the stability and load bearing capacity of foundations, embankments, and other construction projects involving soil.  A higher relative density generally indicates better soil compaction and improved engineering properties, such as increased shear strength and reduced settlement potential.  Conversely, lower relative density suggests looser, less compacted soil that may require additional compaction efforts to meet project specifications.

It's important to note that the method of determining relative density can vary depending on the specific soil and the compaction equipment used. Different standards and tests may be employed in geotechnical engineering to assess relative density based on the project's requirements.

 

relative density of Soil formula
\( D_r \;=\;  e_{max} - e \;/\; e_{max} - e_{min} \)     (Relative Density of Soil) \( e_{max} \;=\; Dr \; ( e_{max}  -  e_{min} ) + e  \) \( e \;=\; - ( e_{max} - e_{min} )  \;  ( 1 - D_r )  \) \( e_{min} \;=\; emax -  ( emax - e \;/\; D_r )   \)
Symbol	English	Metric
\( D_r \) = Relative Density	\(dimensionless\)	\(dimensionless\)
\( e \) = Void Ratio	\(dimensionless\)	\(dimensionless\)
\( e_{max} \) = Void Ratio of the Soil at its Densest condition	\(dimensionless\)	\(dimensionless\)
\( e_{min} \) = Void Ratio of the Soil at its Loosest Condition	\(dimensionless\)	\(dimensionless\)

  

relative density of Soil Classification
Relative Density %	Classification
< 15	Very Loose
15 - 35	Loose
35 - 65	Medium Dense
65 - 85	Dense
> 85	Very Dense