Pile and Pier foundations are two different types of deep foundation used in construction. To choose between these two types of deep foundations a foundation engineer must know the differences between them. The main differences between the pier and pile foundation are given below.
Pile Foundation
Pier Foundation
1
In pile foundation, the loads are transferred by means of vertical timber, concrete or steel.
Pier foundation consists of cylindrical columns to support and transfer large superimposed loads to firm strata.
2
Piles are driven through the overburden soils into the load-bearing strata.
Piers are drilled with the drill machine.
3
Pile foundations transfer the load through friction (in case of friction piles) or through both friction and bearing ( in case of combined end bearing and friction piles).
Pile Foundation exists where there are no firm strata at reachable depth and the loading is uneven
Pier foundation is used where top strata consist of decomposed rock, stiff clays.
6
The types of pile foundation are end-bearing piles, friction piles, compaction piles, anchor piles, tension or uplift piles, sheet and batter piles, etc.
The types of pier foundations are masonry or concrete piers and drilled caissons.
7
Pile foundation is required to resist greater loads like a load of bridge or flyover.
Pier foundations are required for small loading.
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Pile, pier and caisson foundations are three different types of deep foundation used in construction. To choose between these three types of deep foundations a foundation engineer must know the differences between them. The main differences between pier, pile & caisson foundation are given below.
Pier Foundation
Caisson
Pile Foundation
Pier foundation is a type of deep foundation, which consists of a cylindrical column of large diameter to support and transfer large superimposed loads to firm strata below.
Caissons are watertight structures made up of wood, steel or reinforced concrete built above the ground level and then sunken into the ground.
Pile foundation is a type of deep foundation, in which the loads are taken to a low level by means of vertical timber, concrete or steel.
The types of pier foundations are masonry or concrete piers and drilled caissons.
The types of caissons are box, open, pneumatic, monolithic, floating, excavated etc.
The types of pile foundation are end-bearing piles, friction piles, compaction piles, anchor piles, tension or uplift piles, sheet and batter piles etc.
Pier is inserted down to the bedrock.
Caisson is putting a box into underwater and pouring it with concrete.
Pile is a column of material driven by a piledriver.
Pier has a footing.
Caisson doesn’t have a footing.
Pile doesn’t have a footing.
Pier is typically dug out and cast in place using forms.
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:
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
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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.
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The word caisson is derived from latin capsa[1] which means box or case.
In Civil Engineering, Caissons denote watertight structures which are constructed in connection with the excavation for foundations of bridges, piers, abutments in river and lake dock structure, foreshore protection, etc. The caisson remains in its pose and thus ultimately becomes as integral parts of the permanent structure. It can be made up of wood, steel or reinforced concrete, etc.
When Caisson is Required
Followings are the suitable conditions for the caisson foundation:
When the soil contains large boulders, which obstruct the penetration of piles.
When a massive substructure is required to extend to or below the rear bed to provide resistance against destructive forces due to floating objects and score etc.
When the foundation is subjected to a large lateral load.
When the depth of the water level in the river and sea is high.
When there are river forces included in the load compositions.
When the load is needed to carry at the end, caissons are preferred.
When the present groundwater level is aggressive inflow, caissons are suitable.
Mechanism of caisson
Caisson is a box but with no floor underneath it. So, when we put it underwater instead of filling up with water as it is airtight, bubbles form. So as a result, we have a dirt floor from where all the water is kept out. But water is heavy so the surface of the water is exerting pressure on the caisson and try to enter the caisson. So, in order to solve this, we build a platform up in the top and a tube connecting the caisson to the platform that exerts compressed pressure into the surface of the caissons. The front pressure and the chamber pressure equalizes, therefore. The workers climb down in the box and they start digging the dirt out of it. Now if the dirt is taken out manually, all the water will come inside and drown everything. To solve this, we build a pipe full of water. Air pressure from the environment and inside pressure of the caisson keep the water intact in the pipe. Next, the workers send a bucket through the pipe and fill it with dirt and then carried back up. Thus, the workers can dig their way down the riverbed. {adselite}
Box caissons consist of boxes with four sides and a bottom. The top of these boxes is open. The concrete box is fabricated on the ground. Prepared box caissons are floated to the foundation location and placed pre-prepared bases. Once placed in an appropriate place, the whole void space is filled with concrete in such a way that it becomes an integrated part of the previously prepared base.
Box caissons are used for the construction of the bridge pier.
Box caissons are less costly. When it is not feasible to construct on-site types of caissons or economy is required, box caisson serves the purpose.
Excavated Caissons
These kinds of caisson are used to excavate. Cylindrical shaped, these caissons are filled with concrete.
Floating Caissons
These are prefabricated boxes filled with concrete. It is also called a floating docks.
Open Caissons
Open caissons are quite like box caissons. There are two types of open caissons. Top and bottom both open and open top-closed bottom. Soft soil is suitable for these kinds of caissons. Open Caissons are used in the formation of the pier, deep manholes, pump stations, micro-tunneling, etc.
Pneumatic Caissons
Watertight or Box caissons which are used in underwater construction are known as pneumatic caissons.
Compressed Air Caissons
This type of caissons is suitable for parched working conditions where other methods might seem inconvenient.
Monolithic Caissons
The larger size of caissons compared to others.
Construction Process
Following steps could be followed to build a caisson.
We must set the place first for the establishment of the caisson.
Then the first 3.7m of Caisson is pre-casted.
Next, with the help of towboat, the caisson is floated to its location by and tie it to the caisson guide.
After that, concrete is poured using slip forming and as concrete goes, the box becomes heavier and sinks into the water along with the caisson guide.
Mooring cables are used to hold the caissons in place.
When the caisson finally touches the river bottom, the mooring cables are removed.
Caisson is used in building bridge piers as it stays in water almost all the time.
Caisson is constructed in connection with excavation for the foundation of piers and abutments in rivers and lake, bridges breakwater dock structures for the point of view of shore protection, lamp house etc.
It is also used for pump house which is subjected to huge vertical as well as horizontal forces.
It is sometimes used for large and multi-storied buildings.
Pneumatic caisson is used in railway bridges, garbage pits, water supply, sewage facilities etc.
Caisson serves as an impervious core wall on earth dams when placed adjacent to each other.
Caisson provides an access to the deep shaft or a tunnel.
Caisson provides an enclosure below water level for installing machinery, pumps etc.
Caissons have also been used in the installation of hydraulic elevators where a single stage ram is installed below the ground level.
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