In this article we shall discuss three important points about granular sub base (GSB)
1- How can we calculate the required GSB quantity?
2 - What is value of compaction factor for GSB?
3- How much loose thickness of GSB should be taken to get proper compacted layer thickness ?
1- How can we calculate the required GSB quantity?
Let us consider
Length of GSB bed (L) = 500 Met.
Breadth of GSB bed (B) = 7 Met.
Thickness of GSB Layer (T) = 150 mm =0.150 Met.
Max. Dry Density (MDD) =2.221 Gram/ Cubic Centimeter = 2221Kg/ Cubic metre
Note - The value of MDD is calculated by conducting proctor density test as per IS 2720 (part -28) : 1983 (Reaffirmed - May 2015).
Then
Volume of GSB Layer = ( Length of GSB Bed X Width of GSB Bed X Thickness of GSB Layer)
Volume of GSB Layer = L X B X T
Volume of GSB Layer = 500 X 7 X 0.150 Volume of GSB Layer = 525 Cubic Metre
We Know That
Mass = Volume X Density
in this case -
Mass = Volume X MDD
Putting the value in the Formula
Mass = 525 X 2221 Kg
Mass = 11,66,025Kg
To convert above quantity in Tonn
We Know That
1 Tonn = 1000 KG
Then
Mass =(1166025/ 1000) Tonn
Mass = 1,166.025Tonn
Hence required GSB quantity is 1,166.025 Tonn.
2 - What is value of compaction factor for GSB?
Density of Blended aggregate /Density of GSB Mix = 1.60 gram/cc to 2.0 gram/cc
= 1600 - 2000 KG/ cubic metre
In this case
Let us consider
Density of Blended aggregate /Density of GSB Mix = 1.70 gram/cc = 1700 Kg / cubic metre
Value of Max dry density (MDD) = 2.221 gram/cc = 2221 Kg/ cubic metre
Compaction Factor = (Max.Dry Density/Density of Blended Aggregate )
=2.221/ 1.70
=1.307 = 1.30
Hence compaction factor = 1.30
3- How much loose thickness of GSB should be taken to get proper compacted layer thickness ?
Compaction factor = 1.30
Thickness of GSB Layer = 150 mm
Hence
Loose thickness of GSB Layer = ( Compacted layer thickness X Compaction Factor )
= 150 X 1.30
= 195 mm
Hence Loose Thickness of GSB Layer is 195 mm.
Thanks a lot
Mukesh Kumar
Gyan of engineering
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