What is piling in construction?
Piling is the process of driving or boring pile foundations into the ground beneath a building that is under construction. These piles transfer loads from the structure to the ground, helping to support it. Pile foundations are often used where the ground is too weak to underpin the structure.
What are pile foundations?
Pile foundations are long, thin elements generally made of steel or reinforced concrete. They transfer the load through weak, compressible material onto more compact, less compressible stiffer soil or rock at greater depth. The deep insertion of these elements ensures a sturdy base on which the construction project can take place.
Bored piles
Bored piles, also known as replacement piles or drilled piles, are constructed when large holes are drilled in the ground and filled with concrete. Bored piles are very effective as they transfer the load above ground to the deep rock and soil layers below with minimal settlement, which is ideal for supporting structures such as bridges and flood protection.
For some bored piles, the bottom of the hole is widened or under-reamed, creating a bulb at the end. A steel reinforcement cage is lowered into the hole before the concrete is placed or dropped in after the concrete has been poured.
Within the category of bored pile foundations, the two commonly used subtypes are rotary bored piling and Continuous Flight Auger piling:
– Rotary bored piling is used in cases where there are significant obstructions in the ground. A temporary casing is installed by the piling rig to provide support. ‘Pile arisings’ (ground and rock removed via boring process) are removed from inside the casing, then a steel reinforcement cage is installed. At this point, the hole is filled with concrete and the casing is removed.
– Continuous Flight Auger (CFA) piling does not require the use of temporary casing – it is the most versatile, effective and commonly used type of bored pile foundation in the UK. Once the hole has been bored, concrete is pumped in, then a steel reinforcement cage is inserted.
Safe working platforms
Piling rigs are produced in a range of sizes, depending on the type and depth of pile required. Rigs are required to move about and position accurately for each pile location. The area on which the rigs operate is known as the Piling platform. Platforms are usually formed by compacting a layer of coarse, granular fill, to a specified depth. The appropriate fill might be brought on to site or crushed, demolition rubble from site can be used for brownfield developments.
The piling platform is required to distribute the load from the tracks and avoid bearing failure, minimising settlement to ensure safe operation of the rig. Working platforms must be properly designed by a qualified engineer, using soils data and piling rig loading for the specific site. Platforms need to be properly constructed and regularly inspected and maintained by the contractor.
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