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In soil compaction test, if a test result exceeds 100%, should engineers accept the result?

Soil compaction is the process of increasing the soil density by reducing the volume of air within the soil mass.

Soil compaction depends mainly on the degree of compaction and the amount of water present for lubrication. Normally 2.5kg rammers and 4.5kg rammers are available for compaction in laboratories and the maximum dry densities produced by these rammers cover the range of dry density obtained by in-situ compaction plant.


Regarding the second factor of water content, it affects the compaction in the following ways. In low water content, the soils are difficult to be compacted. When water content is increased gradually, water will lubricate the soils and this facilitates the compaction operation. However, at high water content, as an increasing proportion of soils is occupied by water, the dry density decreases with an increase in water content.

For soil compaction tests, the dry density obtained from compaction carried out in-situ by vibrating roller/vibrating plate is compared with the maximum dry density conducted in laboratories using 2.5kg rammer of compaction with similar soils. In essence, the in-situ compaction is compared with the compacting effort of using 2.5kg (or 4.5kg) rammer in laboratories. In case the compaction test results indicate values exceeding 100%, it only means that the in-situ compaction is more than that being carried out in laboratories which is treated as the basic criterion for satisfactory degree of soil compaction. Therefore, the soil results are acceptable in case compaction test results are over 100%. However, excessive compaction poses a risk of fracturing granular soils resulting in the reduction of soil strength parameters.


This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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Kanwarjot Singh

Kanwarjot Singh is the founder of Civil Engineering Portal, a leading civil engineering website which has been awarded as the best online publication by CIDC. He did his BE civil from Thapar University, Patiala and has been working on this website with his team of Civil Engineers.

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7 comments on "In soil compaction test, if a test result exceeds 100%, should engineers accept the result?"

chander bhal roy says:

good site for learning and expressing once view in civil engineering

deepak says:

it is very easy to understand what ever written above.

Nalin Gamage says:

How to perform the compaction test for quarry dust

ela says:

it is possible the degree of compaction is exceed more thean 100% ?

ajay kumar solanki says:


Dhananjay Chavat says:

what are the no of cores to be taken for the particular area to determine in situ dry density density of soil by core cut method

Rico says:

can the base course material be compacted more than 105 %?

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