Techniques and Procedures for Bored Pile (Drilled Shafts)
Bored pile is another type of reinforced concrete pile, which is used to support high building producing heavy vertical loads. Bored pile is a cast-in-place concrete pile where the bored piles have to be cast on the construction site, while other concrete piles like Spun Pile and Reinforced Concrete Square Pile are precast concrete piles.
Drilled shafts are cast by using bored piling machine which has specially designed drilling tools, buckets and grabs, used to remove the soil and rock.
Normally, it can be used by drilling into 50 meters depth of soil. One of the key advantages of a bored pile system us that it won't produce a lot of vibration and the noise level is also reduced when compared to traditional piling systems.
Drilled Shafts Applications
Usually, bored piles, or drilled shafts, are used for those tall buildings or massive industrial complexes, which require foundations that can bear the load of thousands of tons, most probably in unstable or difficult soil conditions. The method of drilling bored pile is different from RC Square pile or spun pile, which is done using a driving method and the piling machine to be used will be different too. Bored piling works require a specialist bored piling contractor instead of using a general piling contractor. There is a simple step-by-step method on how to drill the bored pile in the construction site.
Overcoming Challenges of a Bored Pile System
Like any other deep foundation system, bored piles have also their challenges in order to get them drilled.
Let's start by indicating that the drilling method will depend on the soil type, so you must have a good soil investigation report that will help you decipher which drilling technology will need to be deployed. It is the piling contractor experience, to decide the correct drilling technology and minimize disturbance of the surrounding soil.
For cohesion-less soils such as sands, gravels, silts, and whether it’s under the water table or not, the hole must be supported using steel cages or stabilizing mud such as bentonite suspension.The bentonite solution is really a messy one and you might want to avoid that if possible. Once this process is completed, a reinforcement bar will be dropped into place and concrete will be poured into the bore hole.
Bored Pile Advantages
The main advantages of bored piles or drilled shafts over conventional footings or other types of piles include:
- Piles of variable lengths can be extended through soft compressible or swelling soils, into suitable bearing material.
- Piles can be extended to depths below frost penetration, and seasonal moisture variation.
- Large excavations and subsequent backfill are minimized.
- Less disruption to adjacent soil.
- Absence of vibration will not disturb adjacent piles or structures.
- Extremely high capacity caissons can be obtained by expanding the base of the shaft up to three times the shaft diameter, thus eliminating construction of caps over multiple pile groups.
- For many design situations, bored piles offer higher capacities with potentially better economics than driven piles.
Bored piling is popular to be used in construction as a foundation, especially for bridge work and tall buildings as well. Bored piling work has to be done by specialist bored piling contractor, normal piling contractor cannot execute these type of work without experience and knowledge about bored piles.