METHODOLOGY FOR CONSTRUCTION OF GSB

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METHODOLOGY FOR CONSTRUCTION OF GRANULAR SUB BASE
(Non-Bituminous)
(Acceptance criteria: Ref. Sec. 400 of MORT&H)


Scope:

This work shall consist of laying and compacting well-graded material on prepared subgrade for widening/ new construction of carriageway, hard shoulders, service roads, etc.

Equipment Requirement OF GSB :

  1. Crusher
  2. Wheel loader
  3. Tipper
  4. Grader
  5. Water tanker
  6. Roller

Material OF GSB :

The material to be used for the work shall be crushed stone only. The material shall be free From Organic or other deleterious constituents and confirm to the Grading I given in Table

“The material to be used shall have AIV value not more than 40%. LL not more than 25 &PI value not more than 6% and if water absorption is more than 2%, soundness test shall be carried out.”

Procedure for construction OF GSB :

  1. The sub-base material shall be spread into 2 layers and each layer should be 125mm Compacted thickness on the Approved subgrade with the help of mechanical means to the required slopes and grades.
  2. The moisture content shall be checked and if required any shall be add by sprinkling, within the range of 1% to 2% below OMC.
  3. The material shall be then compacted with vibratory rollers.
  4. The compacted thickness of layer shall not exceed 200mm.
  5. The rolling shall commence form lower edge and proceed towards the upper edge. Each pass of the roller shall overlap 1/3 rd of the preceding. During rolling the grades, cambers are to be checked and any depressions or high spots are to be rectified by adding or removing the material.
  6. The rolling shall be continued till achieving the compaction of 98% of MDD.
  7. Field dry density will be carried out by sand replacement method and recorded.
  8. During the period of construction arrangement of traffic shall be in accordance with MORT&H 112.

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