GRANULAR SUB- BASE

 

 NON-BITUMINOUS BASE COURSES

 

2.1 GRANULAR SUB- BASE

 

2.1.1 Materials: -The material to be used for the work shall be crushed  stone as per the required grading. The materials shall be free from organic or other deleterious constituents and confirm to grading–1 given in table 1(Most Table  400-2), determined by wet sieve analysis.

 

2.1.2Atterberg limit: -As per Clause B2.5.1.2 the material passing 425 micron I.S sieve (0.425mm sieve) when tested according to IS2720 (part-5) by wet sieving shall have liquid limit not more than 25% and plasticity index “zero” or “non plastic”.

 

2.1.3Physical requirements: - The material shall have a 10 % fines value of 50 KN or more (for sample in soaked condition) when tested in compliance with BS 812 (part-111). The water absorption value of the coarse aggregate determined as per IS2386 (part-3). If this value is greater than 2 %, the soundness test shall be carried out on the material delivered to site as per IS383.

 

Table-1: GRADING FOR GRANULAR SUB BASE MATERIAL.

(MOST TABLE 400-1,GRADING-1)

I.S. Sieve Designation	Percent by Weight passing the sieve
75.000mm 26.500mm 4.750mm 0.075mm	100 55-75 10-30 <10
CBR Value (Minimum)                                                  30 %

 

2.1.4 Sampling from Quarry: -

 

Quarry: -100 to 150 Kg samples shall be collected for each source and type of material in the Quarry for various tests. Location of source and Quantity available shall be indicated for approval of source.

 

Table-2 Weight of sample required:-

 

Sl.No	Test	Test method	Minimum weight of sample required (Kg)
1 2 3 4	Gradation Maximum Dry Density C.B.R Liquid and plastic limit	IS2386 (pt-1) IS2720 (pt-8) IS2720 (pt-16) IS2720 (pt-5)	60 30 30 0.5

 

2.1.5 Storage of Aggregate: - Materials shall be stored in such manner that segregation of fine and coarse sizes will be avoided.  They shall be stored /stock piled and handled in such a manner that will prevent combination of foreign materials.

 

2.1.6 Preservation of Approved samples: -

Approved samples shall be preserved in properly labeled wooden boxes.

 

2.1.7 Test Frequency: - Test frequency shall be as given in the table no 3. Maximum dry density shall be carried out on fresh sample for each moisture content using large mould as per clause 5.3 of IS2720 (part-8).

 

    Table No.3: Control Tests and their Minimum Frequency for GRANULAR SUB BASE.

 

Sl. No	Test	Test Method	Minimum frequency	Specification
1	Gradation	IS2720 (pt-4)	One test per 200 cum	Most table 400-2 grading 1
2	Atterbergs limit	IS2720 (pt-5)	One test per 200 cum	L.L=Max 25% P.I=Zero or Non Plastic
3	Moisture content	-	One test per 250 sqm	+1% to –2%
4	Density of compacted layer	IS2720 (pt-28)	One Test (6 holes) per 500 sqm	Min 98%
5	Deleterious constituents	Visual	As required	Nil
6	CBR at 98% at compaction	IS2720 (pt-16)	As required	30% for grading -1
7	Ten percent fine value	BS812 (pt-111)	As required	Min 50 KN.
8	Water absorption	IS2386 (pt-3)	As required	Max 2%
9	Soundness in sodium sulphate & magnesium sulphate	IS383	As required	Max 12% Max 18%
10	MDD & OMC	IS2720 (pt-8)	As required

 

2.2.0   Quality control during  construction:-

 

Following checks and controls shall be made during construction.

 

a)          Base preparation:-  Check that the subgrade already approved is not damaged before laying and during spreading of sub-base material . Subgrade surface shall be free of all vegetation or extraneous matter. Lightly sprinkle with water if necessary, and rolled with two passes of 8-10 tone smooth wheeled roller.

 

b)        Material: -

 

1.      Check that only approved materials are used and there is no segregation of coarse and fine aggregate.

2.      If two materials are to be mixed, the mixing shall be done only at stacking yard. No mixing shall be done on finished subgrade or roadbed. Mixing can be done mechanically.   After mixing the materials at stack yard, the mixed materials shall be checked for gradation.

 

c)         Works: -

 

1.      The thickness of loose spread shall be so regulated by depth block, templates etc., that the compacted thickness does not exceed specified thickness and is laid in camber.  The compacted thickness shall be measured by ‘Depth block’. Trail stretch shall be made to determine efficiency of roller vice-versa the compacted thickness.

2.      Moisture content of loose material shall be checked in accordance with IS 2720(Part-2). The moisture content before rolling shall be +1% to –2% of OMC determined as per IS2720 (pt-8) at a frequency of one test per 250sq m.

3.      After rolling the grade and camber shall be checked as indicated in the drawings.

4.      Field Dry Density (FDD) shall be checked by Sand Replacement Method as per IS2720 (pt-28) using large pouring cylinder. Test frequency shall be one test (6 holes) per 500 m² of compacted area.   Average compaction shall be 98% of MDD (as per IS-2720 Part-8)

 

2.2.1   Longitudinal profile :- +20mm & -25mm (Tolerance)

Control of  alignment and surface regularity shall be checked as per clause  902 of MOST specification.

 

2.2.2 Rectification: -Where the surface is high; it shall be trimmed and re-compacted. Where same is low, the deficiency shall be corrected by adding fresh materials. The rectified surface shall be re-tested.