Pile Foundation – Types & Driving Methods

A pile foundation is a substructure element made up of piles. The piles are responsible for transmitting the structure’s gravity loads to the subsurface.

This type of deep foundation is most commonly utilized in regions where the subsoil is insufficient to sustain the weight of a home or building.

The piles might be composed of wood, steel, or reinforced concrete. The number of piles and their placement are determined by the loads, ground conditions, and other variables.

Types of Piles Based on Their Function

Based on their function the pile foundation piles are classified below:

• Bearing Piles
• Friction Piles
• Sheet Piles

Bearing Plies

Bearing piles are the most common sort of piles, and they are driven into the soil until their ends rest on rock or hardpan below, where they carry the structure’s load vertically. Bearing piles can be made of wood or concrete.

Friction Piles

The frictional or skin resistance between the surrounding soil and the sidewalls of the pile supports the load. In this situation, the piles are not driven into hardpan.

Sheet Piles

This type of pile is primarily employed during foundation building rather than as a foundation element of a structure. Their primary function is to enclose a certain area of the ground within which foundation laying work can be performed, as well as to contain loose soils in order to improve their bearing power.

Types of Piles Based on Materials

Based on the materials the piles are classified below:

• Wooden Piles
• Concrete Piles
• Sand Piles
• Batter Piles
• Iron Piles

Wooden Piles

Wooden piles are widely utilised to offer a low-cost foundation for conventional building projects and in situations where they can remain permanently wet.

Only appropriate wood should be used for this purpose. The diameter of wooden piles ranges from 8″- 18″ and the square section is from 6″ x 6″ to 8″ x 8″.

Drop hammer blows are used to push wooden piles. An iron ring is installed at the top of the pile to absorb the stress of the blows and to keep the timber from damaging.

To aid driving, the bottom end of the pile is pointed and protected by a conical iron shoe. The pile tops are cut off below the permanent low-water level, and a frame work is provided to pour concrete and wall and column footings. Deep excavation, sheet piling, and pumping are frequently required.

Concrete Piles

Reinforced concrete piles are suitable for all permanent projects where significant loads must be sustained. They can be pre-cast or cast in-situ, and they can be used in practically any condition.

Plain concrete piles are also employed for short lengths and are cast by driving a steel tube into a vertical hollow part, which is then filled with concrete.

Reinforced concrete piles are divided into two categories. Precast and cast-in-situ are the most common types.

• Precast Concrete Piles

Pre-cast concrete piles can be constructed in a convenient location away from the construction site and transported to the location where they will be driven.

They’re constantly reinforced to endure the demands of handling and driving. Proper lifting and slinging equipment should be established for the pile, which should be sturdy enough to bear the forces while being transported and driven.

In the manufacturing yard, pre-cast piles are given enough time to cure and build strength.

• Cast-in-situ Piles

These piles are cast on site in the exact location where they will be deployed. These piles are cast by drilling holes in the earth and then filling them with concrete and reinforcement.

Compared to pre-cast concrete piles, cast-in-situ piles offer additional benefits.

Sand Piles

Drilling holes in the ground and then filling them with sand is how sand piles are made. Holes are drilled to the desired depth, and the sand is thoroughly consolidated after filling.

After the piles have been properly consolidated, a concrete cap is installed on top of them to support the load. Sand piles are limited to a length of 10-12 feet and a diameter of 10-12 inches.

Batter Piles

To transfer inclined load and horizontal forces, batter piles will be used. The load on the batter pile is usually assumed to be axial in the preliminary design.

Batter piles are commonly employed in foundations for retaining walls, quay walls, piers, abutments, and chimneys where horizontal stresses are present.

Iron Piles

Iron piles are another type of pile foundation that is often employed. They are classified into two types: disk/disc piles and screw piles.

Disk piles contain hollow shafts up to 12 inches in diameter and a disk up to 6 feet in diameter. They are best suited to sandy or clayey soils with silt.

Screw piles are mostly employed for deeper penetrations. The majority of these piles are driven into the earth using a capstan wheel or drum.

Pile Driving Methods Used For Pile Foundation

The most commonly used pile driving methods are mentioned below.

• Drop Hammer
• Steam Hammer
• Water Jets
• Driving Drum and Winch Crab

Drop Hammer Method

This is one of the simplest and most effective pile driving techniques.

• It consists of a drop hammer that weighs between 2-4 tonnes.
• This drop hammer is raised with the help of a winch and a rope that is linked to it.
• This hammer is lifted to the proper height and then allowed to fall on top of the pile to drive it.
• The top of the pile is cushioned with wooden blocks to protect it from blows.
• So that it may be pushed effectively, the bottom end of the pile is kept pointed and covered with the iron shoe.
• Because they can alter the equipment for driving inclined piles, this method can also be used to drive batter piles.

Steam Hammer Method

The steam hammer method is similar to the blow hammer method, except that the piles are driven using a steam hammer.

In comparison to hammer strokes, steam hammers can deliver a significant number of blows in a short period of time. They’re most commonly utilised to drive sheet piles. They are built with a steel frame that may be used to drive piles with ease.

This method is the most portable and adaptable way to operate in any situation.

Water Jets Method

In this method the water jets are used to drive the piles. These water jets are nozzles that are mounted to the front and sides of the pile shoe.

The high-pressure water that runs through these nozzles softens the loose debris and lubricates the side ones to make driving of piles easier. These water jets can pump up to 100 lbs/sq.in. of water.

Driving Drum and Winch Crab

In clayey soil and homogeneous silt, this method of pile drive is commonly employed for screw piles and disc piles of iron and steel.

The driving drum is fastened at the top of the pile in this approach, and the pile is turned gradually by providing torque through ropes from winch crabs.