CW Milestones Part-4 – Excavation, Layout and Lean concrete

When site is being kicked –off, the site becomes the responsibility of Civil Works. And the period between Kick-off and RFI becomes very crucial for maintaining overall project speed because during this time only one department (i.e. Civil Works) is working on site. For the telecom rollout projects,  this period normally becomes among major bottlenecks, if not handled or planned properly. And the sales and management team has to be thoroughly worked out this period and need to identify for any manageable (contract negotiation/finalization of subcontractors, Sub-con preparedness and their relative brainstorming and trainings in order to be synchronized with targets etc.)  and unmanageable constraints (like offshore supplies of masts or generators etc., shortage of construction material etc in market), before finalizing and sharing targets and deadlines with customers.

The first thing after kick-off a civil subcontractor has to do is to mark boundaries of site, and clear or demolish (if required) the things within parameters.
It then has to mark (limestone powder is generally used for marking) the internal features like location of different foundations specially the tower foundation. And excavate the tower foundation, excavator is required to be used for speed excavations, manual excavations can be done for low cost projects or where targets are not very shrinking. And after that lean concrete should be done for tower/mast foundation. These all processes can take 2 to 10 days after site kick-off depending upon the size of foundation, subcontractors’ working style & methods used and push from vendor  about the speed of work.

Material

Following material needs to be estimated and to be transportation of estimated quantity needs to be ensured before start of processes.

• Gravel Aggregate (50% 3/4” down + 50% 1/2”  standard) (Good quality crush is recommended, should contain broken stones, angular shaped, not plain rounded river stones. The maximum stone size for foundation construction concrete must not be more than 1”)

• Cement (Ordinary Portland cement or Sulphate resistant cement as recommended by DEDs of some locally famous Brand)
• Sand (which Must satisfy the terms defined by local code to be followed like ASTM or as defined by DEDs, in general it should be  coarse, clean, and without stones. Dust should not be mixed in it. It must never be coral sand, and if it is from the sea shore it must be thoroughly washed first and contain no shell or coral fragments. )
• Water (Good for drinking Good for concreting)
• Re-bars (All reinforcement  shall conform to ASTM A 615 Grade 60 steel)
• Binding wires
• Plaster of Paris
• Admixtures (if applicable)
• Shuttering oil

Equipment

Following equipment is normally required in this stage.

• Excavator
• Concrete mixer machine
• Chutes
• Wheel Barrows
• Concrete vibrators (Poker)
• Trowel
• Compactors (Mini Rollers)
• Steel cutting & bending machine
• Steel measuring tape
• Levelling instrument

Manpower

Civil works subcontractor should have following manpower on site in due time.

• Site Supervisor
• Surveyor
• Mixer operator
• Steel fixers
• Mason
• Vibrator operator
• Proper no. Of Labourer etc.

Processes

Following processes are involved in general to achieve this milestone.

1.    After getting all the final approvals and documents/ drawings, the site would be handed over to the contractor for build out. It would be done in the presence of Civil Supervisor, Site Acquisition representative, Sub-con representative and land owner.  The leased area (four adjacent corners) would be marked in front of all parties so as to demarcate the exact and agreed activity area available for construction of site. If the site is not clear like vegetation or some demolishing is to be done, then the land owner would do all the required works and handover the site for subsequent construction.

Site area should be cleared before start of any construction activities

2.    The approved layout is then transferred on to the ground physically with the help of some marking material like lime powder etc. The areas designated for tower, guard house (if applicable) and sharing area would be marked.

  

Clearing of Site Area

Demarcation of site features

3.    A temporary bench mark would then be established which would be governing all the site levels afterwards.

4.    The tower area is then excavated manually or with the help of excavator for foundation up to the required depth with a margin in excavation width in order to provide the proper working space. If water is encountered during excavation then designer would be contacted to get some possible workable solution.

5.    Grounding ring is to be laid at specified depth just after excavation.

6.    The excavated area is then proof-rolled to make the ground compacted.

7.    Lean concrete (1:4:8) is then poured according to the specified mix ratio with the help of mixer machine. Prior to pouring, following must be checked:

a.    Temporary Bench Mark.

b.    Excavation depth. (with reference to BM)

c.    Size of excavation area. (that is matching onsite dimensions with those on drawings)

d.    Materials for concreting. (Material should be enough to complete the whole operation in one go, that is once the leaning process started the workers should not face shortage of any construction material)

Bricks are places to maintain the top level of lean concrete

Pouring of lean concrete

8.    After blinding concrete, the levels are re-confirmed to check the thickness of laid concrete layer.