If test result exceeds 100% in soil compaction, 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.
“Yes, however anything beyond 102% compaction is indicative of the need for either a new “oversized” correction factor or new proctor (maximum density value). Note the use of singular form “test”, if a considerable amount of “tests” were above 100%, I would question the maximum value used for testing. Of course this is all assuming you are using a “modified proctor” (ASTM D-1557) and not a “standard proctor” (ASTM D-698). You can certainly get above 100% consistently when testing using a standard proctor. The standard proctor maximum density value is calculated with less applied energy exerted on the soil during testing…”
— Matthew Dupont (Extracted from internet)
“To some extent, over compaction beyond 100% migh form some cracks due to shear, most of the time the cracks are visible. When such cracks are formed it automatically denotes that the soil has failed. But if the overcompaction has not resulted to failure by forming cracks, the values can.be accepted” —- A-mak Adam (Extracted from internet)
“The soil result is aceptable when compaction result is over 100%,especially if the in-situ compaction result is more than the one carried out in the lab.But excessive compaction poses a risk of fracturing granular soil, thereby reducing soil strenght.” —- Engr Elobenua Endurance Ezenwa (Extracted from internet)
“Comparatively! Yes! But very high values of insitu test above 100% lab value indicate that cracks are very preoccupying. Then care must be taken.” —- Luki Elias Tachuoh (Extracted from internet)
It could be acceptable but the Engineer should ask the question why? In my view this could be confirmed by taking samples from these points for Moisture density relation re-test (proctor) in the laboratory. I would expect the new ref. (MDD) to bring the compaction to 100% or less.