- April 13, 2022
- Posted by: sfpilingadmin
- Category: Blog
Foundations are probably the most important construction steps regardless of what type of infrastructure is being built. Strong and appropriate foundations are imperative for a safe and long-lasting building. They have to withstand the entire load of the superstructure as well as any traffic that is regularly witnessed by a particular building. As with all construction foundations, the main aim of piling or pile foundations is:
- Transmission of foundation load/weight to solid ground
- Resistance to lateral, uplift, and vertical load
Piling is used when the ground soil of a construction site does not possess the right LBV (Load-bearing value) i.e., the soil cannot tolerate the weight of construction. This is usually identified before any construction work is started and is a finding of ground investigation. Volatile moisture content is another factor that makes shallow foundations unsuitable for construction. In such a case, contractors will dig for the deeper layer where the soil quality is better and can withstand the load of the infrastructure. Therefore, construction companies will opt for deep foundations instead of shallow ones. Piling is one such type of deep foundation. Piling foundations may even prove to be less costly in such cases. Piling may also be carried out even if the soil conditions are normal or if there are other considerations such as water. Because of these reasons, piling is a preferred choice of foundations for bridge piers and jetties.
What are piles in construction?
There are different types of piling foundations that contractors may use. The choice depends on a host of factors. Primary concerns include the soil quality, soil type, climatic conditions, type & load of infrastructure, affordability, etc. Even when these factors are feasible, a construction company may use piling to ensure a safe foundation for the superstructure it is going to support. As most of these projects, whether residential or commercial, are expected to have a long life, therefore construction contractors will ensure that only the most suitable and long-lasting foundation techniques are used. The selection process is highly technical and complex, prompting engineers to do complex calculations before deciding on the most suitable foundation.
End bearing piles
End bearing piling is one of the most commonly used piles construction methods. In this type, the piles are designed as columns that transfer the load to a much stronger and firm stratum; like rock, gravel, or dense sand which is located deep below the structure’s base. They take advantage of the hard compacted soil which lies at the bottom of the pile. Even when the soil is very weak, the chances of a pile failing are next to zero. Sometimes, however, the soil adjacent to the pile may stick to the pile and cause “Negative Skin Friction” caused because of groundwater drainage and soil consolidation.
Cohesion or friction piles
This type of piling uses skin friction for the transmission of their weight/load to the ground soil. Piles are driven near each other for reducing the compressibility and the porosity of the soil around these piles. This is why it is also known as compaction piles. During the
pile driving process, the soil partially loses its strength and becomes moulded. As a consequence, piles cannot transfer the intended load immediately after being driven. However, the soil usually regains a part of its strength in around 3-5 months after being driven.
Timber piling has been used since antiquity and is still used in regions where timber is available in abundance. It is highly appropriate for providing piling to embankments as well as cohesion piling. However, the timber used for piling should be in the best condition. It is also important that timber should not be driven into hard ground. Timber piling is kept lower than the level of groundwater to protect it from putrefaction and decay. Timber piles construction is protected through the process of Pressure creosoting.
Pre-cast/pre-fabricated concrete Piles are another effective method of piling. They are usually prepared in circular, octagonal, square or triangular forms. Usually, short lengths of concrete piling are produced. They are pre-casted to be easily connected for acquiring the desired length. This method does not decrease the load capacity. Usually, Reinforcement is required for withstanding both the driving stress and handling. Pre-stressed concrete piling is becoming a popular choice with time instead of the traditional pre-cast concrete piling.
Steel/ Iron piles are highly suitable for driving in as well as handling
long lengths. They have small cross-sectional areas and high strength which makes drive penetration much more convenient even in firm soil. They are easy to cut off and can be easily joined through welding. Cathodic protection or tar coating is carried out to prevent any risk associated with low pH soil which can act as a corrosive agent. There are other ways of prolonging the corrosion process to over 50 years.
The combination of more than one material in piles construction is also a common strategy to overcome a multitude of challenges. For instance, timber piling is combined with steel piling to protect the timber from the effects of water. Concrete can also be used with timber instead of steel.
Advantages of Piling
- Many Piling techniques result in low settlement and this makes them a preferred choice for multi-storey infrastructure projects.
- Various types of pilings can be precast for meeting the required specifications.
- They can also be prefabricated and made in any shape, size, length, which reduces the project completion time.
- Piling methods such as the End bearing piling free from buckling failure even in weak soil.
- In many techniques, the pile is supported by a firm stratum which is stronger than steel.
- Most of the piling methods are less costly.