While you’re discussing about different types of pile foundation, it is important to know about Franki Pile.
A pile is a long, slender member which is used to transfer the load of building to a suitable bearing stratum and provide overall support to the structure. A pile foundation is more common foundation nowadays. This type of foundation is preferred for multi-story building where loads are heavy or when soil of high bearing capacity is available at some depth.
There are different types of piles depending upon the function and load transferring mechanism. A Franki pile is one of them. Here in this article, we will discuss its Installation, advantages and disadvantages.
A Franki piling also known as pressure injected piling system is a technique used to drive expanded base concrete pile. It is a cast in place concrete pile constructed using a drop hammer and temporary casing. The Franki piling system was first introduced in 1909 by Belgian Engineer Edgard Frankignoul.
This type of pile is primarily used where high bearing capacity soil is located deep below the surface or where an unusual high load transfer is required. These piles can also be used as perpendicular piles or raking piles. Franki piles have enlarged based to improve the absorption of tensile loads and have low noise and ground vibration level.
Franki Pile Applications
Franki piles can be used for different types of soil conditions and for buildings under different loading conditions. Some of its applications are
- Foundation with tight settlement limits
- Heavy duty surfaces
- Dock bases
- Bridge construction
- Crane runways
- Wind energy installations
- High rise buildings
Fabrication of Franki piles
These types of piles are in situ concrete driven piles with retrievable casing tubes. The casing tube is fitted at the bottom with waterproof seal in the form of plug of dried concrete. A hammer is attached with crane and fall freely from suitable height inside the casing and hammer strike the concrete plug which result in driving of casing tube is soil. The number of blows per meter length will be an indication of load bearing capacity of soil on site.
After achieving the desired depth or ramming criteria the plug is removed and then volume of concrete is driven in to some length. The volume of expanded base can be calculated on the basis of bearing capacity of soil and load of pile which is expected to transfer to soil. The tube casing pulled up and more concrete in driven in. Then reinforcement cage is installed, and concrete filled in and the tube is retracted.
Advantages of Franki Piles
Some of the advantages of cast in place Franki piles are given below
The adaptation of various designs to suit the soil types and construction location enable maximum usage with regard to load bearing capacity and pile length. Franki pile is used in construction sector for more than 100 years as a result of high-performance standard and outstanding economic viability.
The Franki pile is fabricated on site with the help of crane and drop hammer is used for the displacement of soil and making a hole in the soil for construction of pile. This method is environment friendly because it does not involve extraction of soil which prevent breaking up soil and it also does not involve any emission or waste. This type of pile foundation is found successful in construction areas prone to contamination.
If the soil at the required depth does not have sufficient load bearing capacity, then soil improvement can be carried out by gravel pre compaction. In this form of soil improvement pounding in gravel both above and below the intended pile casing land depth. After the completion of gravel pre compaction the pile is rammed in to the intended depth and construction of Franki pile can begin.
Low noise emission
The Franki pile is constructed on site with the help of using casing tube, hammer and crane. The concrete is prepared in mixer on site. This method does not produce any noise and pile is constructed safely without damage. While in some other methods where pre cast concrete piles are used these types of piles are driven in ground with the help of different hammers supported by crane. This pre cast pile driving in soil produce noise and can also produce additional stresses in concrete pile.
This method is very economical as compared to some other piles fabrication methods. In this method there is very less chance of wastage of concrete. Similarly, the steel reinforcement cage is also made on site and then driven into the hole. So, it saves cost in terms of preventing wastage of concrete and steel.
No need of transportation of soil
This method involves displacement of soil with the help of plug of dry concrete attached on the bottom of casing tube. The hole is made to required depth with the help of plug and this method does not involve any excavation of soil. So, in this method there is need of transportation of soil.
Good resistance to settlement
The Franki pile consist of wide base at the bottom and the soil in contact with base is properly compacted which increases its bearing capacity and also reduced chances of settlement. The wide base of pile at bottom distributes the load on large area and minimize the chances of settlement.
Disadvantages of Franki Pile
Quality control and storing of material issue
The Franki piles are cast in situ piles. The material for the construction of pile should be stored in small warehouse and should be fully covered because contact of material with moisture can result into compromise of quality control of concrete. So, all the concrete material specially cement bags and reinforcement should be covered and protected from moisture.
Ground water table problem
In some areas the underground water table remains near ground surface. This can disturb the construction of in situ concrete pile if flow of underground water is heavy.