At a given input of condensation energy there exists a relationship between moisture content or water content and dry density, as shown Figure 1,

On the dry side, the added water forms a thin film of water coating the surface of the particles which is a . provides smoothing effect Under the influence of the compaction effort that has on them enables them to move closer to each other. This results in a reduction in the air gaps that continue till we reach the peak at which we get maximum dry density ,Id max) The corresponding moisture content is being called optimum moisture content ,OMC,

Fig. 1 Moisture Content Dry Density Relationship
Fig. 1 Moisture Content Dry Density Relationship

The added water beyond the summit begins to occupy the pore space preventing soil particles from entering that space. As a result the dry density starts decreasing from the peak value. Related moisture content a . Is optimum and not a maximum value unlike dry density which is a maximum value. curve Figure 1 is called’Moisture Content-Dry Density Curve‘ or just compaction curve,

The moisture content corresponding to the ascending part of the condensation curve is denoted as dry side of the optimum and which corresponds to the descending part wet side Why the best?

zero air zero curve

Zero air vacancies a. are in line with degree of saturation (s) 100%, interrelationship ID, woo And s, is as follows

?D = g*woo , [1+(G*W/S)]


?D = dry density of soil

Yes = specific gravity of soil solids

?woo = unit weight of water

woo = water content of soil

s = degree of saturation

the substitute s = 1 (100%) we can get ID for different values ​​of woo and plot the result which is also shown in Figure 1 symbolised by ‘zero air zero curve‘ or saturation curve,

This figure shows that the zero air void is a theoretical limit that can never be reached in practice, indicating that it is impossible to completely remove the pore air or allow the soil to become completely saturated in the compaction process. Impossible to do.

The above equation can be used to plot W-γD relation to the different values ​​of s Like 95%, 80% etc.

Effect of change in overall effort

If we gradually increase the compaction effort and plot the corresponding compaction curves, the results will be as follows: line drawing number 2,

Fig. 2 Effect of condensation energy on dry density and OMC
Fig. 2 Effect of condensation energy on dry density and OMC

The maximum dry density increases with a decrease in OMC with an increase in intensive effort, both of which are favorable outcomes. These results automatically reverse the sign on the decreasing side of the compaction effort.

article written by

Dr. Nain P. Kurien

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.