This is an in-depth guide to pile foundation.
In this guide, you’ll find everything about pile foundation. That includes:
- What is the pile foundation?
- Components of pile foundation
- Types of piles
- Factors affecting the selection of pile type
- Uses of pile foundation
- Advantages and disadvantages, and
- Pilling methods.
So, if you are:
- A civil engineer
- Or working in the building construction sector,
- Or at least want to learn about the pile foundation system.
Then read on…
What Is Pile Foundation?
Basically, pile foundation is a type of deep foundation.
Actually, it is a long and slender column.
And, it is used to transfer imposed loads to the desired depth of hard soil.
Components Of Pile Foundation
Generally, a pile foundation has two components – Pile, and Pile Cap.
Piles carry loads deep into the ground.
And, the pile cap is a solid foundation on which columns are then built.
Basically, a pile cap is built on a group of piles.
Function Of Pile Foundation
Mainly, pile foundation does two things:
- Transmit loads to a solid soil layer.
- Resist vertical, lateral, and uplift load.
Types Of Pile Foundation
Piles can be classified depending on various criteria.
Let’s see them:
Based on function or use:
- Bearing piles
- Friction piles
- Sheet piles
- Tension piles
- Batter piles
- Fender piles
- Compaction piles
Let’s discuss these types of piles:
These piles act as columns and transfer loads by their tips.
That’s why they are also called End Bearing Piles.
Generally, they penetrate through the soft soil layer and their tips rest on a hard stratum.
These piles transfer loads by their skin friction.
This kind of pile is used when a hard stratum is available at a greater depth.
This type of piles is driven into the ground to provide excavation support and earth retention.
These piles form a wall-like structure interlocking with each other.
These piles are constructed to resist the uplift forces by anchoring down the structures.
These piles are also called Uplift piles or Anchor piles.
These piles are constructed at an inclination.
They resist large horizontal or inclined forces.
These piles are constructed in sea or river.
They protect water structures against impact from ships or barges.
And they are normally made of timber.
As the name says, compaction piles are driven to compact the soil layer.
And, thus increasing the bearing capacity of the soil.
These piles don’t carry any load themselves.
Pile Types Based on materials:
- Concrete piles
- Composite piles
- Steel piles
- Timber piles
- Sand piles
Concrete piles are three types:
Precast Concrete Piles
Precast concrete piles are prepared on the ground before being driven.
After gaining strength, they are driven into the ground using heavy machinery.
Cast-In-Situ Concrete Piles:
Unlike precast piles, cast-in-situ piles are constructed where they are actually needed.
And, this is done in two ways – Cased and Uncased.
Prestressed Concrete Piles:
These piles also are precast piles.
In these piles, pre-tensioned cables are put inside the piles.
Doing this reduces the size of piles.
In this type of pile, two different types of materials are used.
For example, a timber pile is used in the lower part and a precast concrete pile in the upper part of the pile.
This pile can carry up to 100 tons.
A steel pile can be a rolled section, a fabricated shape, or a piece of sheet pile.
Two or more sections of sheet piles may be connected together in a box shape and driven as one pile.
A timber pile is a trunk of a tree, trimmed of branches.
Usually, this type of piles is used as a foundation for structures with moderate loads, ranging from 15 to 25 tons per pile.
These piles are also used as a foundation for temporary structures.
These piles are mainly used for soil improvement.
In this pilling, sand or similar material is installed into the soft ground via a casing pipe.
Type of Pile Based On Construction Method:
- Driven piles
- Driven and cast-in-situ piles
- Bored and cast in situ piles
- Screw piles
If piles are installed by impact hammering, vibrating, or pushing into the ground those are called driven piles.
They are made from preformed material having a predetermined shape and size.
Read More: An Essential Guide To Driven Piles
Driven And Cast-In-Situ Piles:
Driven and cast-in-situ piles are constructed by driving a casing with a detachable base plate into the soil.
Depending on the application, a rebar cage is suspended inside the tube after the casing has been driven to the desired depth.
Next, a measured quantity of concrete is poured or pumped into the casing.
Following this, the casing is withdrawn by means of driving or vibrating.
Where applicable, a short rebar cage can also be pressed into the concrete afterward.
Bored And Cast In Situ Piles:
Bored cast in situ pile is constructed by digging a hole in the ground by suitable means such as percussive or rotary method with the use of temporary or permanent casing or drilling mud.
After that, the construction is finalized by filling the hole with reinforced concrete.
These piles are wound into the ground, much like a screw is wound into the wood.
They can be installed quickly with minimal noise and vibration.
So far, you’ve learned about different types of pile foundations.
Now, let’s see what are the…
Factors Affecting The Selection Of The Pile Type
- Loading conditions
- Nature of structure
- Soil properties
- Groundwater table
- Availability of materials and equipment
- Length of pile required
- Facilities available for pile installation
- Availability of funds, etc.
Uses Of Pile Foundation
Pile foundation is used in the following situations:
- If a high groundwater table exists beneath the structure.
- When the superstructure’s load is high and non-uniform.
- If highly compressible soil is present at shallow depth.
- If the structure is located near the river bed or seashore.
- When a canal or deep drainage system passes near the structure.
- When the soil condition is very poor and it is not possible to excavate the soil up to the desired depth.
- If it becomes impossible to keep the foundation bed dry by any measure due to heavy inflow of seepage.
Advantages Of Pile Foundation
Following are some advantages of pile foundation:
- Pile foundation can be pre-ordered.
- It reduces construction time.
- Suitable for all sizes of land.
- Suitable for deep installation.
- Pile foundations are best for wetlands.
- It is long-lasting.
- Pile foundation is good for places where drilling and creating holes are tough.
Disadvantage Of Pile Foundation
Like any other foundation, pile foundation also has some disadvantages.
Here are some of them:
- A pile can be damaged by driving through stones and boulders.
- Piles can be attacked by marine borers in saltwater
- A pile cannot be above ground level.
- It is very difficult to know the actual required length in advance.
- Vibrations generate when piles are driving which affects the neighboring structures.
- Heavy equipment is required for driving the piles.
- Pile is not containable for low drainage.
Installation Methods Of Pile Foundation
Basically, there are two methods of installing piles:
- Driving, and
Driving Method (Displacement Piles):
In this method, piles are driven, pushed, or otherwise installed into the ground without first excavating the area.
The piles are installed using this method is called displacement piles.
The technique used in this method are:
- Dropping weight (Impact hammers)
- Vibration (Vibratory hammers)
- Jacking (restricted to micro-piling)
Boring Method ( Non-Displacement Piles):
In this method:
First, a borehole is made into the ground.
After that, steel reinforcement is inserted into the hole.
Finally, the borehole is filled with concrete.
The piles installed using the boring method are called non-displacement piles.
The technique used in this method are:
- Continuous Flight Auger (CFA)
I hope this guide helped you learn everything about pile foundation.
But before you get started on the construction field, I’d like to hear from you.
What did you think of today’s post?
Or maybe you have a question about something you read.
Let me know by leaving a comment below…