bored pile foundation

Bored Pile Foundation – Advantages, Disadvantages & Techniques

Bored pile also referred to as drilled shaft at some places is a kind of reinforced-concrete base that holds frameworks carrying heavy vertical loads in place. A bored pile is basically the concrete cast-in-place, which means that the pile is cast on the site of the building. The arrangement varies from other concrete foundation designs, such as spun pile or reinforced concrete square pile foundations, which make use of concrete precast platforms. Bored piling is used extensively for bridge construction, tall buildings, and other large industrial projects, which all require deep and intensive bases.

Apart from the foundation systems, Bored piles are also used to build formative underground barriers for earth retention. Piles may be stacked next to each other, with 75 – 150 mm gap in-between— referred to as contiguous pile wall, or they can be positioned in a way that they coincide, creating stable and robust fencing, often used to regulate groundwater movement.

Bored Pile Advantages

The key benefits of drilled-in shafts or bore piles over traditional pile foundations are:

  • Piles of different lengths can be easily extended into an appropriate bearing material working its way through soft, loose, or swelling topsoil.
  • Piles can be lengthened to depths below the penetration of frost and varying periodic dampness.
  • The need for massive excavations and the subsequent backfilling gets considerably reduced
  • There is less perturbation to neighbouring regions while the work is in process.
  • The turbulence generated during bore pile foundation is relatively minimal, thus reducing the disruption of piles or buildings standing adjacent to it.
  • Large capacity caissons can be built by extending the base of the pile shaft up to 3 times its circumference, thus eradicating the need for covers over multiple pile assemblages.
  • A Bored Piling company can deliver higher capacities with possibly better profitability than the conventional pile arrangements for several design requirements.

Bored Pile Disadvantages

Here are a few disadvantages associated with bore pile foundation.

  • Like in every other deep foundation structures, bored piles provide the contractor with many challenges. As the drilling method used depends greatly on the type of soil, the contractor needs to perform a comprehensive analysis of the soil at the place of proposed piling and report it. Land tests need to be conducted before augering starts to prevent taking out the potentially polluted soil. The contractor relies on the soil report and his/her previous experience to pick the best drilling method, which will minimise the disturbance.
  • Sometimes, a piling company might be required to do some chiselling through buried blockages. In that case, it may cause significant commotion and vibrations— thus nullifying one of the prime USPs of bore pile, which happens to be the minimal disruption.
  • Bore pile or drilled shaft is one of the slowest forms of piling processes, with an average working time of around eight weeks. With such a painstakingly long procedure, the project ‘s cost is most likely to take a leap. Besides, owing to the extended working timelines, the workforce and the neighbouring areas are also opened to lengthened noise exposure periods.
  • Any projects requiring piling underwater in pebbly/granular soil may involve driven steel enclosures, which would once again result in additional noise pollution and widespread commotion.
  • If the soil type is pretty loose, such as with sand, gravel, and silt, or the borehole stretches well below the water level, a piling company needs to use steel cages or sustaining mud such as bentonite suspension to protect the opening. The solution can be very long and complicated and imparts a considerable level of complexity to the project.

Bored Piling Technique

Bored pile deployment begins by drilling a vertical opening into the earth, using a bore piling tool. In order to extract the soil and rock, the device can be equipped with specially built drilling equipment, buckets, and aces. Piles can be drilled-in up to 60 meters deep and up to 2.4 meters in diameter. The procedure may include swerving a makeshift steel cylinder or sleeve into the earth, which remains intact at the upper part of the pit till the pile is poured.

Once the hole is dug, a steel reinforcing rebar structure is constructed and lowered into the pit, which is then filled with the concrete. In order to sustain the construction, the top of the pile may be covered with a footing or dock near the ground level.

Bored pile foundation work must be undertaken by skilled and experienced contractors from a reliable Piling company only as it is a highly specialised job requiring widespread expertise and practice in the construction and engineering of bored piles as well as a thorough knowledge about the working condition of soil and piling location.