A drilled pier is a large diameter concrete cylinder built in the ground. For construction of a drilled pier, a large diameter hole is drilled in the ground and subsequently filled with concrete.
The difference between a drilled pier and a bored pile is basically of the size. Generally bored piles are of diameter less than or equal to 0.6m. The shafts of size larger than 0.6m are generally designated as drilled piers. A drilled pier is a type of deep foundation constructed to transfer heavy axial or lateral loads to a deep stratum below the ground surface. The transfer of load to the soil from a drilled pier, like a pile, can take place through end bearing, skin friction or a combination of both.
Advantages of Drilled Pier
Drilled piers has so many advantages over piles. Some advantages of drilled pier are listed below.
- As a single drilled pier can take up the load of a group piles, it is more convenient.
- Drilled piers have higher resistance to lateral loads than piles.
- Construction of drilled piers generally requires lighter equipment for drilling than that for pile driving.
- There is no noise due to hammer blow in the case of drilled piers.
- Piles drivven by a hammer casue ground vibrations and ground heaving. Such conditions do not exist in the case of drilled piers.
- The base of a drilled pier can be enlarged to provide greater bearing capacity and also to provide greater resistance to uplift.
- Drilled piers can be used even when the soil contain boulders etc.
Disadvantages of Drilled Pier
Drilled pier has some disadvantages too. The major disadvantages are given below.
- The concreting operation requires stricter supervision. The quality of concrete are generally inferior to that in precast piles.
- Deep excavation of the drilled piers, if not properly supported, can cause substantial subsidence and damage to adjoining structures.
- Subsurface investigations required in the case of drilled piers are more than that in piles.
- Load tests in the case of drilled piers are difficult.
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