Pilings

Pilings

1. Friction Piles

   • In Cohesionless soil: Applied load is transferred to the surrounding soil mainly through skin friction along the surface of the piles
   • In Cohesive soil: Whole load on the pile is transferred to the surrounding soil along the pile surface through skin friction and only a very small part through the pile toe.

2. End Bearing Piles

   • Piles driven down to a layer with high bearing capacity, the applied load is transferred from the pile to the surrounding soil mainly through the pile toe.

3. Function: To transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata having a high bearing capacity

4. Classification of piles

   • Displacement piles: Piles are driven or pushed, vibrated or screwed into the ground, displacing the soil outwards and downwards but no materials are removed.
     • Driven Piles: Preformed unit driven into the soils by the blow of hammer
       • Advantage of performed unit – can be inspected and checked as a sound structural member before it is driven into the ground
       • Materials: Timber, Concrete or Steel.
         • Timber
           • 1) Usually square sawn timber of sizes 225 x 225 to 600 x 600mm.
             • 2) Fitted with an iron or steel driving shoe to prevent splitting due to driving, and have iron ring around the head to restrict ‘brooming’ of the pile head due to overdriving
               • 3) Not suitable of driving through dense strata or strata with obstruction.
           • Characteristics:
             • 1) Free from short or reverse bends, large or loose knots, slake, splits and decay.
               • 2) Uniform taper from the butt to tip.
         • Precast Concrete
           • 1) Precast Reinforced Concrete Piles – made of concrete statically cast in uniform section before driving into ground and reinforced with steel bars.
             • 2) Precast Pretensioned Concrete Piles - made of concrete statically cast in uniform section & suitably reinforced with pretensioned prestressing steel
               • 3) Precast Pretensioned Spun Concrete Piles – hollow pile made of concrete cast by centrifugal spinning. Suitably reinforced with pretensioned prestressing steel
           • Problem encounter when using this pile in urban area
             • 1) Can set up unacceptable noise or vibration
               • 2) Many urban sites are themselves restricted or congested
         • Steel Piles
           • H Section Piles
             • Disadvantage - tendency to bend on the weak axis during driving.
           • Box Piles
         • Driven and Cast in Place Piles
           • 1) Economically formed in diameter of 300 to 600 mm and can carry loads of up to 1300kN.
             • 2) Required heavy piling rig, open level site and site where noise is restricted.
   • Replacement piles: A hole is form in the ground by removal of material from the ground and thus material is displaced by a concrete material formed in the ground.
     • BORED and CAST –IN- PLACE PILES
       • Suitable to use in sites where piling work to be carried out close proximity to existing building or where vibration or noise restricted.
     • Percussion Bored Piles
       • Suitable for clay and / or gravel subsoil.
     • Rotary Bored Piles
       • Suitable for most cohesive soil e.g. clay
     • Grab Construction - Cased
       • Sand and gravels with high demands on casing technology
     • Rotary Drilling with kelly -Cased
       • Used in all types of soils
     • Rotary Drilling with kelly – Borehole supported by hydrostatic pressure
     • Rotary drilling using twin rotary head – Front of Wall
     • Rotary drilling using flight auger – Continuous flight auger system
     • Composite Piles
       • 1) ‘Prestcore’ pile
         • 2) Shell pile
           • 3) Cased pile
     • Pile Test
       • Load Test

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