Field Density Test – FDT Test (Sand Cone Method):
In this article, we will discuss how to perform field density test or fdt test at the site.
The sand cone method is one of the most common methods that are used for fdt or field density test in highway construction. The dry density test is carried out in the field to check the compaction of the layers.
Compaction is very useful for preparing the sub-base grade and other layers of pavement. Compaction is done in the construction of embankment to increase stability as well as for decreasing the settlement.
In field compaction, the compacting moisture content should be controlled first and the adequacy of rolling should be controlled by checking the achieved dry density and comparing it with the maximum dry density.
Base layer – 98%
Sub base layer – 98%
Type 1 layer – 95 %
ABC layer – 100%
Procedure Of FDT Test:
The steps to perform fdt test are as follows:
1. First, take the weight of the empty sand cone and then fill it with dry sand and then weigh again.
2. Collect the excavated soil from the hole and measure the weight.
3. After weighting, collect the specimen of soil to determine the water content in it.
4. Now place the sand cone on the test hole with the help of the base plate and allow the sand to run by opening the control valve.
5. When the sand stops running, close the valve and weight the cone with the existing sand. Finally, calculate the dry density of the soil by given the below formula. If the test fails, compact, and perform the test again.
Calculation For FDT Test:
The volume of the hole = Mass of sand in hole/Density of used sand.
Wet density = Mass of wet excavated soil/Volume of hole
Dry density = Wet density × 100%/ Moisture content of soil + 100
Degree of compaction = Dry density × 100%/Maximum dry density.
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