A Pier foundation is one of the types of foundation mainly used for bridges, dams, and other large structures. It is also used in the construction of tall buildings. In this article, we will discuss what is a pier foundation along with pier foundation types, advantages, foundation piers construction details, and preferred location of piers.
What is a Pier Foundation?
A pier foundation is a collection of large-diameter cylindrical columns to support the superstructure and transfer large super-imposed loads to the firm strata below. It stood several feet above the ground.
Pier footing transferred the load of the superstructure to the underlying soil or rock. It is constructed by digging a hole in the ground and then filling it with concrete or stone.
It is also known as “Post foundation” of "Column Foundation".
Piers are often used in areas where the ground is not stable enough to support other traditional foundation types.
Types of Pier Foundation
Depending on the material used for the construction, there are four types of pier foundations. These are:
Depending on the structural configuration, there are four types of pier foundations.
Masonry Piers
Masonry piers are one of the most popular foundation types for both residential and commercial buildings. They are extremely durable and can last for many years with proper maintenance. They are made from concrete, brick, or stone and are typically reinforced with steel rods or rebar.
Masonry piers are typically used for buildings that are located in areas with high soil-bearing capacity. They are also often used in areas where the ground is not level or where there is a high water table. They can be built on any type of soil, but they are most commonly used on sandy or clay soils.
Concrete Piers
A concrete pier foundation is a type of foundation that uses piers made of concrete to support a structure. The piers are typically placed at regular intervals underneath the structure and are often used in conjunction with other types of foundation, such as a footing foundation.
Concrete pier footings are extremely strong and can support a large amount of weight. They are also resistant to fire and termites. They require very little maintenance and can last for many years with proper care.
Timber Piers
Timber piers are another popular type of foundation for both residential and commercial buildings. They are made from pressure-treated lumber and are typically reinforced with steel rods or rebar.
Timber piers are typically used in areas with high soil-bearing capacity. They are also often used in areas where the ground is not level or where there is a high water table. Timber piers can be built on any type of soil, but they are most commonly used on sandy soil or clay soils.
Steel Pier Foundation
A steel pier foundation is a type of deep foundation that is used to support structures that are built on soft or unstable ground. Steel piers are driven into the ground until they reach a firm layer of soil or rock. The steel piers foundation is then connected to the structure using steel cables or rods. This type of foundation is often used for bridges, buildings, and other large structures.
Drilled Caissons or Piers
Drilled caissons usually refer to the cylindrical foundation. A drilled caisson is largely a compressed member subjected to an axial load at the top and a reaction at the bottom. There are three types of drilled caissons:
- Concrete caisson with enlarged bottom
- Caisson of steel pipe with concrete filled in the pipe
- Caissons with concrete and steel core in the steel pipe
Beam and Girder Piers
Beam and girder pier foundations are suitable for small bridges and buildings. In this type of foundation, the pier is constructed by using a beam or girder. The beam or girder is supported by columns. The columns are either round or square in shape. The beam or girder pier foundation is suitable for small bridges and buildings.
Column and Cap Piers
Column and cap pier foundation is suitable for medium and large bridges. In this type of foundation, the pier is constructed by using a column. The column is supported by a cap. The cap is either round or square in shape. The column and cap pier foundation is suitable for medium and large bridges.
Slab Piers
A slab pier foundation is suitable for buildings. In this type of foundation, the pier is constructed by using a slab. The slab is supported by columns. The columns are either round or square in shape. The slab pier foundation is suitable for buildings.
Pile Piers
A pile pier foundation is suitable for bridges and buildings. In this type of foundation, the pier is constructed by using a pile. The pile is driven into the ground. The pile pier foundation is suitable for bridges and buildings.
Advantages of Pier Foundation
Pier Foundation is found in coastal areas. There are many advantages of it:
- This method is easy and requires less amount of materials and labor. The materials required here are easily available
- It has a wide range of variety when comes to design. There are varied materials we can use here to increase the aesthetic view and also it remains in our budget
- Pier foundation save money and time as it doesn’t need extensive excavation and a lot of concrete
- It causes minimal disruption to the soil environment. a shovel can be used for excavation and existing roots and soil organisms remain mostly undisturbed. At the end of the building's useful life, the site will be easier to restore to a natural state than a site with a full basement.
- As it lifts the house above the ground, floods cannot do any damage to the structures.
- The space between the house and the ground is enough to install utilities like plumbing and electrical wires among them.
- Workers can easily get under the space between the house and the ground to solve issues related to plumbing and electrical as there is enough space to crawl.
- It’s comfortable to walk on a floor that doesn’t rest on a firm surface and it is good for people who have arthritis and back pain
- Inspection is possible as the diameter of the shafts is larger
- Engineers can change the design whenever they want if necessary
- The ground vibration that is normally associated with driven piles is absent in the case of drilled piers construction.
- Bearing capacity can be increased by under-reaming the bottom (in non-caving materials).
Pier Foundation Construction Details
Followings are the foundation pier construction details:
Spacing of Foundation Piers
Pier foundations usually are built 1-1.5 feet above the ground. This gap (how far apart are foundation piers) is necessary to prevent moisture as the moisture damages the wooden structures.
Shape and Size of piers
The shape of the piers is:
- Square
- Rectangular
- Circle
The diameter of piers is usually 6 in, 8 in, 10in, and 16in. The depth of the piers foundation is below the freezing depth. The depth is around 5-6ft.
Ways of Performing
There are many ways to do a pier foundation. Masonry is the most convenient way among them. But the process is not ideal. The stack of bricks is not directly put together in the hole. The fold pillar is completely on the ground, then lower into the wall, and does not look fast and enjoyable.
Materials Used
Wood, Brick, concrete, etc. are used in the pier foundations. But the most used material is reinforced concrete. It provides the most compressive strength and has a high tolerance for tensile strain. Furthermore, reinforced monolithic pillars can withstand any type of frosting and will not crack under these forces. And it is quite easy to dilute the concrete mixture and pour it into the holes.
Types of Cross-Section
There are many types of foundation pillars’ cross-sections. It can be a cylindrical, helical or box-shaped, or more complex form with the broadening of the bottom of the posts. The broadening can increase the area of the base and thus increase the load-bearing capacity of the foundation. The weight of the house will be distributed over a larger area.
Technologies of Pier Foundation
The most used way consists of digging a square or rectangular hole. The size of which is 4-8 inches longer than the required diameter of the post. Then formwork is set in the pit which settles the shape of the future foundation; then the reinforcement cage is placed, and concrete is poured. After that, the formwork is removed and covered with a pillar. This technology has made it possible for us to make a reinforced concrete pillars of different shapes but requires a relatively substantial number of earthworks and the use of removable shuttering. Installation of every new post for the foundation is the following - in the dug well we set formwork which propped up the sides of the spacer. Inside the formwork, there is the reinforcement cage. The reinforcement cage makes sure that the reinforcements remain in place.
Grillage
The top of the pier foundation which connects the individual posts into a single structure is called grillage. When heavy structural loads from columns, piers, or stanchions are required to be transferred to the soil of low bearing capacity, a grillage foundation is used. Grillage is often found to be lighter and more economical.
Suitable Condition for Pier Foundation
Pier foundation is used in the below conditions:
- When decomposed rocks are present in the top strata, and there are underlying strata of sound rock below them, in such conditions pier foundations, are used.
- As stiff clays offer a lot of resistance when driving a bearing pile, piers foundations can be conveniently used in such situations.
- It is used if the house is built from log, timber, or frame as the pillars are small relative to other foundations
- If a structure needed to be built on a slope, a pier foundation is used
- The soil must have a low bearing capacity of water unless the pillars will sink under the weight of the house
FAQ
What are the differences between masonry and concrete pier foundations?
Masonry piers are made from concrete, brick, or stone and are typically reinforced with steel rods or rebar. Concrete piers are made from concrete only.
Masonry piers are typically used for buildings that are located in areas with high soil-bearing capacity. Concrete pier foundations are typically used for buildings that are located in areas with low soil-bearing capacity.