Construction Methodology of Granular Sub-Base

Construction Methodology of Granular Sub-Base

1.    NAME OF ACTIVITY:

     GSB Laying

 2.  Highway Activities

  3.  References:

a)       Ref. to Technical Specification (MORT&H Spec. & Amendments)

a.1)    Section : 400

a.2)    Tables:   400-1, Grading -V.

b)      Ref. other related works prior to this activity:

b.1)   Sub grade top layer level Recording, Stock Approval.

c)       Ref. to Drawing(s):

c.1)    Nil

d)      IS/IRC Specifications

d.1)   Nil

     4.  SCOPE OF WORK:

    This work shall consist of laying and compacting well-graded material on prepared sub-grade in accordance with the requirements of the specifications. The material shall be laid in two layer according to lines, grades and cross sections shown on the drawings or as directed by the Engineer.

     5. MANPOWER REQUIREMENT:

1.     Section In charge

2.     Site In charge

3.     Section Engineer

4.     Site Supervisor

6.     MACHINERY REQUIREMENT:

·        Bull Dozer or Tractor Dozer

·        Motor Grader

·        Vibratory Smooth drum roller

·        Tipper truck 6cum/14cum

·        Water tanker with sprinkler (Tractor mounted or truck mounted)

7. SEQUENCE OF WORK (For Both layers separately):

Step 1:        Transporting and Dumping of Granular Sub-base material.

Step 2:        Spreading of granular Sub-base

Step 3:        Final grading, checking of level and compaction.

Step 1 - Transporting and Dumping of Granular Sub-base material.

Granular Sub-base (GSB) shall be transported from the stone quarry / Stock Yard to the site by means of tipper trucks.

Step 2 - Spreading of granular Sub-base

The GSB shall be spread by a tractor mounted or wheel dozer or motor grader or its equivalent. The thickness of the GSB shall be thick enough so that the dozer blade should not accidentally damage the sub-grade after compaction required thickness will be achieved.

Step 3 - Final grading, checking of level and compaction.

Motor Grader shall be utilized to carry out the leveling and grading to ensure uniform thickness. Water sprinkling is to be done to meet OMC at site before compaction starts. The compaction to be done from the lower to upper edge of the GSB by overlapping the one third of the drum width of the compactor. Final trimming shall be carried out when vibratory roller applied to compact the GSB layer as soon as the grading and levels are met. The speed of the roller shall not exceed 5 km/hr. Rolling shall be continued till the density of 98% achieved of the maximum dry density for the material determined as per IS:2720 (Part 8).

8. SURFACE FINISH AND QUALITY CONTROL OF WORK :

1.     Surface tolerance + 10mm and –20 mm of the design levels of the GSB (as per MOST Clause 902.3 Table 900.1).

2.     Field Density to be achieved is 98% of MDD.

9. MEASUREMENT FOR PAYMENT :

Granular Sub-base shall be measured as finished work in position and it shall be paid as per BOQ item No.3.01.

10.  CONCLUSION :

The above methodology shall form as a guide to the site engineers and supervisors to ensure good construction practice. All works should be in accordance to the specification mentioned in the Contract. The method adopted may change to suit the site conditions and sequence of work if the need arises.

Upon completion of the laying of GSB top layer, the site is available for laying of Wet Mix Macadam road base layer.

11.  SAFETY AND ENVIRONMENTAL ACTIVITIES :

a)     Caution Boards will be placed at the beginning and end of working site and also at risky locations.

b)    Signal man will be placed at heavy traffic locations at the time of Execution.

c)     Reflective sign boards will be placed during night near risky locations.

d)    All necessary measures shall be taken to control the disposal of all forms of waste generated by the construction operations and in all associated activities.

e)     All necessary measures and precautions shall be taken to avoid any nuisance or disturbance arising from the execution of the work.

  

12.  OTHER POINTS THE CONTRACTOR LIKES TO  MENTION :

a)     The manpower & machinery proposed is indicative only. The requisite quantity of resources may vary based upon site condition.

b) Any modification in execution of activity shall be done with prior              information with consultant.