Piling is one of the essential elements used in the construction industry for transferring loads evenly from a building structure into the ground.
In this guide, you will learn about piling and piles foundations, uses of pile foundations, history, and types of piles. You will also get information about the types of pile foundations, the difference between bored and driven piles, and the installation methods for piles. Moreover, this article also covers how piling helps in bridge construction and what piling platforms are.
Understanding Piling & Piling Foundations
Piling is the procedure in which pile foundations are bored or driven into the ground under a building’s structure that is being constructed. These piles help transfer loads from the constructed structure to the ground, providing optimum support. These are primarily used on soil that is too weak to bear the loads of a building structure.
The thin and long steel or reinforced concrete elements are laid in series to form pile foundations. These help transfer load through weak and compressible material onto a relatively compact and less compressible, stiffer soil or rocks at greater depth. These are inserted deep inside the ground to make a sturdy base for construction work.
Where Are Pile Foundations Used?
Pile foundations can be installed in the grounds where the groundwater table is high and heavy and non-uniform loads are needed to be imposed on the soil. These foundations are ideal to use when the soil at shallow depth is compressible and where there is a possibility of scouring due to the location of the construction site near the river bed or seashore.
Pile foundations are also suitable for installation in areas with a canal or a deep drainage system near the constructed structure. It is also recommended to be used at construction sites where soil excavation up to the desired depth is impossible because of poor soil conditions. Moreover, these can also be installed in soils with a heavy seepage inflow.
What Is the History of Piling?
The history of piling dates back to hundreds and even thousands of years. Around 6000 years ago, Switzerland’s river dwellers used piled foundations for building structures and elevating the dwellings on to defend against flooding and attack. Almost 2000 years ago, the Romans also used piles made of timber and drove them into the riverbed for constructing bridges in London and Corbridge and to carry out shore works in Europe and the UK.
The piling technique was used in early civilisations to build cities and towns over the swampy soil near rivers for better communication, structural fortification, and protection with added strength. At that time, timber piles were inserted into the ground by digging holes and filling sand and stones inside them.
In today’s world, land with poor soil characteristics is also exploited by development agencies and authorities to build new structures by forming pile foundations.
Types of Piles Based on Their Working Principles
These are the two main kinds of piles
End Bearing Piles
These piles help in transmitting loads deeply and directly to the firm soil or rock layer beneath their lower end.
Friction Piles
These piles help transfer load by developing friction between the surrounding soil and their surface area over the entire length.
Types of Pile According to Their Construction Methods?
A pile foundation involves the columns arranged in series which act as the structural base, while piles are the columns or cylinders that help transfer the load to the subsoil. Piles in the foundation work together, ensuring that piling provides optimum support to the solid and heavy loads. The following are the four main types of pile foundations based on their unique construction methods:
Aggregate Pile Foundation
Aggregate piles are also known as stone columns, meaning a pile is formed using compacted aggregate. For this type of pile foundation, a hole is bored to insert the casing in which aggregate is dropped in the form of layers which are then compacted after removing the casing. The bearing capacity of the surrounding soil is improved by forcing the aggregate sideways.
Bored Pile Foundation
Bored piles are also named as drilled piles or replacement piles. These foundations are constructed by drilling large holes under the ground surface and filling concrete. They help in transferring the load from above the ground surface to the deep layers of rock and soil. They transfer load with minimum settlement and areideal to support large structures, such as bridges.
The construction of a bored pile foundation varies based on different ground conditions. Sometimes, the bottom hole of piles is made wide to create a bulb at the lower end. Then, a steel reinforcement cage is placed inside the hole before pouring concrete.
The bored pile foundations are of two further types:
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Rotatory Bored Piling
It is utilised in the grounds with considerable obstructions and involves the installation of a temporary casing in the form of piling to provide the required support. Pile arisings are taken out from the casing before the installation of a steel reinforcement cage. After that, the casing is removed for filling the concrete inside hole.
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Continuous Flight Auger (CFA) Piling
This type of pile foundation does not involve the utilisation of temporary casing and is one of the most commonly used types of bored pile foundations. This technique involves the formation of a hole inside ground surfaces in which concrete is poured, and then a steel reinforcement cage is inserted into it.
Driven and Case In-Situ Pile Foundation
This type of pile foundation can be constructed by using two methods. One method involves the use of permanent casing in which a corrugated and reinforced thin steel tubular casing is driven into the ground surface with the help of a mandrel present in the casing. After putting the casing in place, the mandrel is removed, and concrete is poured into the casing to form a composite pile of concrete or steel.
The other method uses a temporary casing called the Franki type. In this method, a steel reinforcement cage is placed inside the casing, which is removed after placing dry concrete mix. The concrete is compacted, and some of it is forced out of the casing’s bottom side to form an enlarged bulb, which helps to enhance the pile’s bearing capacity.
Driven Pile Foundation
Driven pile foundations can be constructed with timber for coastal works, sea defence and jetties. It can be constructed using precast concrete piles reinforced for withstanding driving stress. Moreover, it can also be constructed by interlocking the piles made of steel in the form of tubular, box, or H section for constructing walls.
For laying a driven pile foundation, the piles are driven into the soil with an equal volume of soil displaced sideways, which ultimately compacts the soil around the pile to increase its bearing capacity. The pore water pressure is dissipated through rapid drainage to ensure soil strength. This type of piling cannot be done in saturated or silt soils because they have slow drainage and do not allow proper compaction.
Differences Between Bored Piles & Driven Piles
The driven piling technique involves driving piles into the soil to enhance its bearing capacity. These piling foundations are constructed off-site and put in place on-site, making them rapid to build and use. The installation of these foundations produces lots of vibrations, making them unsuitable for compact sites.
On the other hand, a bored piling technique involves drilling holes in the ground and pouring concrete inside them. These piling foundations are thus constructed on-site. Forming these piling foundations does not create much disturbance in the soil structure, allows better bearing capacity, and prevents seasonal problems like frost penetration.
How Are Piles Installed During Construction?
Hammering, jacking, or vibrating techniques are used for installing driven piles inside the ground. It involves using percussion hammers, hydraulic drivers or rams, or vibratory drivers. This specialised equipment helps reduce ground resistance, allowing the piles to slide into the ground quickly.
On the other hand, a continuous auger having a diameter from 300mm to 900mm is used for installing bored piles. However, a larger diameter of 1200mm can also be used for large-diameter piles.
How Does Piling Help in Bridge Construction?
Usually, the installation of piles is done beneath bridge abutments and piers to provide the necessary foundation and support, enabling the constructed structure to bear the weight. The method of installing piles for land bridges differs from those for bridges constructed over a water body.
The installation of piles for constructing a bridge over a water requires constructing a cofferdam, a waterproof enclosure. After that, water is pumped out of the enclosure, allowing the pile’s placement.
What are Piling Platforms?
Based on the depth and type of pile, different sizes of piling rigs are produced, which need to be moved and positioned accurately for each pile. The operational area of rigs is known as the piling platform, which is formed with a compacted layer of coarse, granular fill up to a specific depth. This piling platform helps load distribution from the tracks and prevents bearing failure with minimised settlement to ensure safe rig operation.
The engineers require information related to soil data and piling rig loading for a particular location to design an appropriate working platform.
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