PILING

PILING

1. Functions

   • transferring the load from the structure to the foundation at deeper depth when the soil's bearing capability is sufficient to support the structural load.

2. Friction piles

   • in cohesive soil : skin friction transfer practically the whole load on the pile to the surrounding soil along the pile surface, with the pile toe transferring only a minor portion.
   • In cohesionless soil; skin friction along the piles' surface transfers the applied load to the surrounding soil. The pile toe also carries a significant portion of the load. The relative density of the soil and the shape of the pile are the main factors that influence skin friction resistance.

3. End bearing piles

   • The applied load is carride from the pile to the surrounding soil primarily through the pile toe when piles are driven down to a layer with 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 blows of hammer
       • Materials
         • Timber
           • Characteristics
             • 1. free from short / reverse bends, large / loose knots, slake splits & decay
               • 2. uniform taper from the butt to tip
           • usually square sawn timber of sizez 225 x 225 to 600 x 600mm.
           • easy to handle and driven by percussion or drop hammer
           • timber pile not suitbale of driving through dense strata or strata with obstruction
         • Concrete
           • lengths up to 18m with section sizez ranging from 250 x 250mm to 450 x 450mm carrying loadings up to 1000kN
           • Problems (urban area)
             • 1. transporting the complete length of pile through narrow / congested streets
             • 2. the driving process - percussion can set up unacceptable noise / vibration
           • Types
             • 1. Precast Pretensioned Spun Concrete Piles - hollow pile by centrifugal spinning
             • 2. Precast Reinforced Concrete Piles - reinforced with steel bars
             • 3. Precast Pretensioned Concrete Piles - reinforced with pretensioned prestressing steel
         • Steel
           • DRIVEN and CAST IN PLACE PILES
             • - suitable where the length of pile required varies.
               • - economically formed in diameter of 300 to 600 mm and can carry loads of up to 1300 kN
                 • - required heavy piling rig, open level site and site where noise is restricted
           • Types
             • H-section pile - in the form of wide flange sections
               • disadvantage - tendency to bend on the weak axis during driving
             • Box piles - fabricated by welding together steel plates
   • 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
     • Composite Piles
       • Prestcore pile - formed inside a line bored hole
       • Shell pile - suitable in waterlogged and soft substrata
       • Cased pile - using steel strip / plate; formed into a continuous helix
     • Factors of selection piles
       • 1. Durability - precast concrete pile suitable to use in marine condition, while timber is rejected
       • 2. Ground Condition - influence the pile types and techniques
       • 3. Location & type of structure
     • BORED and CAST-IN-PLACES PILES
       • Percussion Bored Piles - Suitable for clay / gravel
       • Rotary Bored Piles - suitable for most cohesive soil; clay
     • DRIVEN and CAST-IN- PLACE PILES
       • 1. Necking - due to ground water movements washing away some of the concrete
       • 2. Ground heave - caused by displacement of the soil by the drive tube
     • 1. Rotary Drilling with kelly - cased
       • used in all types of soil
       • use where site conditions are restricted
     • 2. Rotary Drilling with Kelly - Borehole supported by hydrostatics pressure
     • 3. Rotary Drilling using twin rotary head - Front of Wall
     • 4. Rotary drilling using flight auger - Continuous flight auger system

5. Load test

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