Granular Sub-base - Grade of Granular Sub-base (G.S.B)

 Granular Sub-base: 

G.S.B - It is the layer which is used after the embankment construction. Its also known as Sub-base layer.

G.S.B

IS Sieve Designation	Percent by Weight Passing by IS Sieve
	Grading I	Grading II	Grading III	Grading IV	Grading V	Grading VI
75.0 mm	100	-	-	-	100	-
53.0 mm	80-100	100	100	100	80-100	100
26.50 mm	55-90	70-100	55-75	50-80	55-90	75-100
9.50 mm	35-65	50-80	-	-	35-65	55-75
4.75 mm	25-55	40-65	10-30	15-35	25-50	30-35
2.36 mm	20-40	30-50	-	-	10-20	10-25
0.85 mm	-	-	-	-	2-10	-
0.427 mm	10-15	10-15	-	-	0-5	0-8
0.075mm	<5	<5	<5	<5	-	0-3

 

Use of GSB by Grade

Grading (III) and (IV) shall preferable be used in lower sub-base.

Grading (V) and (VI) shall be used as a sub-base cum drainage layer.

The thickness of each layer shall not be less than 150mm.

The minimum thickness of drainage as well as filter layer shall be 100mm.

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