In engineering, 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. Normally2.5kg rammers and4.5kg 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 using2.5kg rammer of compaction with similar soils. In essence, the in-situ

compaction is compared with the compacting effort of using2.5kg (or4.5kg) rammer in

laboratories. In case the compaction test results indicate values exceeding100%, 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 over100%. However,

excessive compaction poses a risk of fracturing granular soils resulting in the reduction of

soil strength parameters.