Compaction factor can reach above 100% in various cases and can have a different meanings.
before going to compaction factor lets look at how it comes into picture.
We do calculate the level of compaction base on test we did on the actually compacted earth and comparing it with the one which we sent for testing at third party laboratory for getting the values of MDD and OMC.
When we send a sample of soil / earth / murrum to a third party laboratory.
they do perform a compaction test on it at varying moisture content in it.
The data of test result is then plotted on a graph.
as we know the compacted density can increase with increase water content in it up to some extent beyond which the density of soil starts falling down.
this makes a curve on a plotted graph paper where we look for highest density achieved and its corresponding moisture content.
highest reach on a graph is maximum dry density of that material denoted as MDD
to achieve that what was the water content in it is Optimum moisture content denoted as OMC. above and below OMC the value of density going to get drop.
Now we know the properties of material which we are using for doing filling work in structure.
If the material which we are using for doing filling is different from one we have tested before for its properties, there will be difference either on plus or minus side in compaction factor.
compaction factor is level of compaction we achieved compare with a standard value which we had achieved in lab testing.
Calculation of moisture content in the sample also an important parameter, if the value calculated goes wrong, it will also impact on the compaction factor calculations.
When we find there is something wrong happened in doing testing we should retest it by doing sampling at different location in same patch.
Factors that can affect compaction factor result
1. Material used for filling is not same as which we had tested in third party lab or own lab for MDD and OMC.
2. If doing sand replacement test, the density of standard sand need to be verify before each test and also the value of mass of sand in cone should be re-verified.
3. Moisture content in material should be calculated correctly as this makes direct impact of the dry density of the soil.
4. If there is an error in weighting scale it can also make impact on the results.
5. If there is some mixing or say some stones got into the material which are taken from test pit, it will also impact the result on plus side (when we do work practically at construction side, there are the chances of mixing of other material in material which we are using for filling. this is not a small scale work where we can assure about there will not be any contamination of other material in it) - in such cases we can verify by examining sample taken from test pit only in case when compaction factor is on plus side.
Before using any material for doing filling work, it is important to verify its properties like MDD and OMC.
In absence of those values or referring values which are not of that material, you either get results on pus or minus side and difference can be actual difference in those properties of material which can be a smaller or very big.
