GRANULAR SUB BASE

GSB MATERIALS

  • MATERIALS TO BE USED:- NATURAL SAND, CRUSHED GRAVEL, CRUSHEDSTONE, CRUSHED SLAG OR THE COMBINATION OF THESE DEPENDINGUPON GRADING REQUIRED.

  • BRICK METAL, KANKAR & CRUSHED CONCRETE SHALL BE PERMITTED IN LOWER SUB-BASE.


  • THIS WORK SHALL CONSIST OF LAYING & COMPACTING WELL GRADED MATERIALS ON PREPARED SUBGRADE IN ACCORDANCE WITH THE REQUIREMENTS OF THESE SPECIFICATIONS & CROSS-SECTION SHOWN IN THE DRAWING OR AS INDICATED BY ENGINEER-IN-CHARGE.

  • THE MATERIALS SHALL BE LAID IN ONE OR MORE LAYER AS LOWER SUB BASE & UPPER SUB BASE.



GRADING FOR GRANULAR SUB-BASE MATERIALS


NOTES:-

1. GRADING III & IV SHALL PREFERABLY BE USED AS LOWER SUB- BASE.

2. GRADING V &VI SHALLBE USED AS A SUB-BASE-CUM- DRAINAGELAYER.

3. GRADING TO BE ADOPTED SHALL BE SPECIFIED IN PROJECT

4. WHEN THE SUB-BASE IS IN 2 LAYERS i.e. LOWER & UPPER SUB- BASETHICKNESS OF THE LAYER SHALLNOT BE LESS THAN 150MM.

5. IF THE WATER ABSORPTION OF THE AGGREGATES > 2% THE AGGREGATES SHALL BE TESTED FOR WET AGGREGATE IMPACTVALUE(AIV)


PHYSICAL REQUIREMENTS FOR MATERIALS FOR GRANULAR SUB-BASES


CONSTRUCTION OPERATIONS

PREPARATIONOF SUB-BASE:-

PRIOR TO THE LAYING OF SUB-BASE FOLLOWING APPLICATIONS SHALL BE COMPLETELY FINISHED:-

  • SUBGRADE SHALLBE PREPARED BY REMOVING ALL VEGETATION & OTHER EXTRANEOUS MATERIALS.

  • LIGHT SPRINKLING OF WATER

  • ROLLED WITH 2 PASSES OF 80-100KN SMOOTH WHEELED ROLLER


SPREADING & COMPACTINGOF SUB-BASE:-

1. SUB-BASE MATERIALS & WATER SHALL BE MIXED MECHANICALLYBY SUITABLE MIXER.

2. CONTROLLED ADDITION OF WATER SHALL BE DONE TO OBTAINHOMOGENEOUS & UNIFORM MIX.



3. THE MIX SHALL SPREAD ON THE PREPARED SUB-GRADE WITH THE HELPOF MOTOR GRADER OF ADEQUATE CAPACITY. (HAVINGHYDRAULIC CONTROLS FOR MAINTAING SLOPES )


4. MOISTURE CONTENT OF THE MIX SHALL BE CHECKED IS:2720(II).

5. AT THE TIME OF COMPACTION IT IS FROM 1-2% BELOW THE OPTIMUMMOISTURE CONTENT.

6. AFTER MIXING ROLLING SHALL BE DONE BY APPROVED ROLLER.


SPREADING & COMPACTING OF SUB-BASE:-


IF THE THICKNESS OF COMPACTED LAYER DOESN’T EXCEEDS 100MM:- 80-100KN SMOOTH TYRE ROLLER


FOR COMPACTING SINGLE LAYER UPTO 200MM- VIBRATORY ROLLER



7. ROLLING SHALL BE COMMENCED FROM THE LOWER EDGES & PROCEEDS TO WARDS THE UPPER EDGE(CROWN).

8. EACH PASS OF THE ROLLER SHALL UNIFORMLY OVERLAP NOT LESS THAN 1/3RD OF THE TRACK MADE IN THE PRECEDING PASS.

9. ANY HIGH SPOTS OR DEPRESSIONS SHALL BE CORRECTED BY REMOVING & ADDING MATERIALS.

10. THE SPEED OF THE ROLLER SHALL NOT EXCEED 5KM/HR.

11. ROLLING SHALL BE CONTINUED TILL THE DENSITY ACHIEVED IS AT LEAST 98% OF THE DRY DENSITY FOR THE MATERIAL.

12. ALL LOOSE, SEGREGATED OR DEFECTIVE AREAS SHALL BE MADE GOOD TO THE FULL THICKNESS OF THE LAYER AND RE-COMPACTED.


MEASUREMENTS FOR PAYMENT:-

  • GRANULAR SUB-BASE SHALL BE MEASURED AS FINISHED WORK IN POSITION IN CUM.

  • NO EXTRA PAYMENT SHALL BE MADE FOR THE PROTECTION OF EDGES OF GRANULAR SUB-BASE EXTENDED OVER THE FULL FORMATION SHALL BE CONSIDERED INCIDENTAL.







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