Bored pile foundation or drilled shaft foundation is a commonly used foundation for supporting heavy vertical loads. It transfers the load to the soil below or rock strata with sufficient bearing capacity and reduces the settlement of the structure.
The construction of the bored pile is divided into two phases: the drilling phase and the construction phase. In the drilling phase, the spoil is removed to form a hole of the required diameter and depth, while during the construction phase, the reinforced concrete is poured in situ. Therefore, bored piles are also called replacement piles.
Bored piles are popular in urban areas where minimal vibration is a prerequisite during construction. Moreover, it is employed where the headroom is limited, the depth of the piles remains the same, and there is no risk of heaving.
This article explains the construction process, challenges, and advantages of bored pile foundation.
Bored Pile Construction Process
The bored piling process involves the following stages:
- The construction starts by drilling a vertical hole into the soil using the bored piling machine. The machine is outfitted with accessories like drilling tools, buckets, and grabs that help remove soil and rocks during the drilling process.
- The piles drilled can go up to a depth of 60 m and a diameter of 2.4 m.
- A temporary steel cylinder or sleeve is inserted into the drilled hole until the pile is poured.
- After this, a rebar cage for the pile is inserted into the hole and, subsequently, filled with concrete.
- The top of the pile is capped either with a footing or a pile cap near the ground level so that the structure above can be constructed.
Bored piling work is a specialized operation that requires extensive knowledge and experience in bored pile construction, soil and site conditions, etc. Hence, it is advised to have the work performed by a bored piling contractor.
Bored Pile Construction Challenges
The main challenges faced during bored pile construction are:
- The contractor must perform a thorough investigation of the soil to study its properties. The soil type decides the drilling method to be used for the construction.
- Sometimes, the piling contractor completely relies on the past reports and the soil investigation reports to choose a method that causes fewer disturbances to the soil nearby.
- When the drilled hole extends below the water table, additional support must be given using steel cages or stabilizing mud. This is the main challenge faced with cohesionless soils like sand, gravel, and silt.
- The drilling of the hole and pile construction on cohesionless soil is complex and causes a mess.
Advantages of Bored Pile Construction
The main advantages of bored piles are mentioned below:
- Bored piles facilitate easy movement of the piles to variable depths irrespective of the soil type. It extends the pile till the bearing strata is approached.
- Bored pile works best in soft, compressible, and swelling soils.
- Bored pile foundation can be extended to depths below seasonal moisture variation or frost penetration.
- Bored pile foundation prevents the need for large excavation and subsequent backfilling.
- Bored pile foundation does not disrupt the adjacent soil drastically.
- Vibration and related disturbances due to bored pile foundation construction are relatively low compared to conventional foundation methods.
- Bored pile foundation offers higher bearing capacities compared to other driven piles.
FAQs
The construction of the bored pile is divided into two phases: the drilling phase and the construction phase. In the drilling phase, the spoil is removed to form a hole of the required diameter and depth, while during the construction phase, the reinforced concrete is poured in situ. Therefore, bored piles are also called replacement piles.
The main challenges faced during bored pile construction are:
1. The contractor must perform a thorough investigation of the soil to study its properties. The soil type decides the drilling method to be used for the construction.
2. Sometimes, the piling contractor completely relies on the past reports, and the soil investigation reports to choose a method that causes fewer disturbances to the soil nearby.
3. When the drilled hole extends below the water table, additional support must be given using steel cages or stabilizing mud. This is the main challenge faced with cohesionless soils like sand, gravel, and silt.
4. The drilling of the hole and pile construction on a cohesionless soil is complex and causes a mess.
The main advantages of bored piles are mentioned below:
1. Bored piles facilitate easy movement of the piles to variable depth irrespective of the soil type. It extends the pile till the bearing strata is approached.
2. Bored pile works best in soft, compressible, and swelling soils.
3. Bored pile foundation can be extended to depths below seasonal moisture variation or frost penetration.
4. Bored pile foundation prevents the need for large excavation and subsequent backfilling.
5. Bored pile foundation does not disrupt the adjacent soil drastically.
6. Vibration and related disturbances due to bore pile foundation construction are relatively low compared to conventional foundation methods.
7. Bored pile foundation offers higher bearing capacities compared to other driven piles.
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