Franki Pile Construction and Applications: Geotechnical Engineering

This report provides a detailed overview of Franki pile construction, a common type of deep foundation used to transfer building loads to stable soil layers. It begins with an introduction to pile foundations and their categorization, highlighting the unique characteristics of Franki piles, which are high-capacity, cast-in-place concrete piles constructed using a drop weight and casing to form a bulb. The report outlines the step-by-step procedure for constructing Franki piles, including driving the tube, base formation, and building the shaft using either compacted or cased methods. It also discusses the importance of reinforcement and pile group configurations for stability. Furthermore, the report presents typical dimensions and capacities of Franki piles, along with their advantages, such as high bearing capacity, improved side friction resistance, and low noise emission. Finally, it touches on the broad applications of Franki piles in bridges, high-rise buildings, docks, and industrial structures. This document is available on Desklib, a platform offering a variety of study tools for students.

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CONSTRUCTION OF FRANKI PILES
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CONSTRUCTION OF FRANKI PILES
Introduction.
Pile foundations are the most common types of deep foundations so far known. (Day,
2006) Described piles as relatively long, slender, column-like members that are used to transfer
building loads to the deeper safer soils.
Piles are most suitable in situations where there is weak soil layer on the surface. The
strata cannot bear to carry the loadings from the building and hence, bypassing weaker strata and
then be transferred to stable ground below. According to (Rajapaske, 2008), piles are categorized
into two, that is non-displacement and displacement piles. Displacement piles are those that shift
the soil when they are being pushed into the ground while Non-displacement piles are those that
the steel case is withdrawn after concreting of which examples include Alpha piles and vibrex
piles
FRANKI PILES.
(Coduto, 2001) states that ‘Franki piles are high capacity; cast-in-place concrete
constructed using a drop weight or hammer and a casing, which forms a bulb’. The concrete that
is used as a casing must be stiff to take the ramming effect. The ramming effect increases the
load bearing capacity by compacting the surrounding soils.
The piles have an enlarged base in dry concrete and cylindrical shaft. This pressure
injecting footing foundation was pioneered by Edgard Frankignoul, a Belgian Engineer in 1909
just before the second world war and has since gained fame worldwide since then with much
transformation (FRANKI Grundbau GmbH & Co. KG, 2010)

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Franki piling system is most preferred due to its maximum tensile strength, minimized
noise during construction and low ground vibrations.
PROCEDURE OF CONSTRUCTING FRANKI PILES.
(Coduto, 2001) Describes the following procedure for the construction of Franki piles:
Step 1: Driving
Construction starts by drive tube being inserted into the ground provisionally. The drive
tube diameter ranges between 300-600 mm. The contractor achieves this through top-driving
method or the bottom driving method.
In top driving method, the drive tube is driven with a bottom plate temporary mounted on
it to the desired depth by the help of the diesel pile hammer. Later, the steel plate will be
removed when the concrete will be pounded through the drive tube.
On the other end, bottom-driving method involves hammering a drive tube which has a
low-slump concrete at its bottom. Next, the plug is stricken continuously hence pulling the tube
into the ground.
Step 2: Base Formation
The drive tube is held in place by cables once the required depth has been reached. Then,
little injunctions of concrete are placed into the tube and driven through the ground. This process
is achieved through recurring blows using the drop hammer. The hammer falls through a height
of 6 m and its weight ranges between 1400 and 4500 kg. At the end, concrete bulb will be
molded in the soil. This process is continued until a certain volume of concrete is reached using a
specific number of blows.

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Step 3: Building the Shaft.
The shaft extends the pressure injected footing to the stable ground surface. The shafts
generally used are Compacted shafts or cased shafts.
Building compacted shafts involves adding charges of concrete simultaneously with
raised drive tube in increments. In due time the surrounding soil is compacted leading to
increased resistance of side friction and end bearing resistance.
On the other hand, the cased shaft is built by inserting the steel covering into the drive
tube, compacting the concrete lump and then withdrawing the tube. Lastly, the cover is filled
with standard concrete. The method is economically cheaper than the other one for piles longer
than about 9 m though it does not develop much load capacity. Cased shafts are mandatory if
very soft soils are encountered. This is because the soil does not provide the lateral support
required for the compacted shaft method.
Below are diagrams showing the above-described procedure.
Figure 1 Franki Pile Installation

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(Fleming, et al., 2008) Recommends that in order to avoid uplift of the shaft and the
lateral loads, reinforcement is mandatory for both shafts during construction. Also, the space
between the tube and drop hammer must be in such a way to allow the reinforcing cage to fit for
the hammer to fall freely
In order to achieve maximum stability (Venkatramaiah, 2006) states that the piles can be
installed in groups of two or more and connected with a pile cap. Individual pile can also be
installed but they are not very stable.
The table below given shows the typical dimensions and typical capacities of the Franki
pile foundations.

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Franki
Pile
Type
Typical
Allowance
Downward
Capacity
Base diameter Nominal Shaft Diameter
Compacted Cased
(k) (kN) (in) (mm) (in) (mm) (in) (mm)
mini 100 450 24 -30 600 -750 N/
A
N/A 10.6 -11.1 270 -280
medium 200 900 34 -40 850 -1000 17 430 12.2-14 300 -360
standard 400 1800 34 -40 850 -1000 22 560 16-17.6 400-450
large 500 2200 34 -40 850 -1000 23 580 19 480
maxi 600 2700 34 -40 850-1000 25 630 22 560
Table 1 TYPICAL FRANKI PILE DIMENSIONS AND CAPACITIES.
Advantages of Franki Piles
According to (FRANKI Grundbau GmbH & Co. KG, 2010) the advantages of the Franki
piles include the following:
1. The piles have a high bearing capacity due to the increased strength that is achieved
during construction. This is because the surrounding soils are compacted when the
pile is being installed. Therefore, it can be concluded that these piles are best
applicable for all kinds of soils especially sand.
2. These piles have an improved side friction resistance hence eliminating the challenge
of lateral support as stated by (FRANKI A Keller Company, 2018). This is attributed
to the rough interface produced between the compacted soil and the shaft during
construction.

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3. Franki pile have an additional end bearing area as a result of enlarged bases which are
bell like that come as a result of construction process.
4. There is low noise emission during ramming as compared to head hammering.
5. The pile has limitations in settlement depth as compared to other types of
foundations.
6. These piles are very economical because of reduced concrete and steel quantities.

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Application.
( Mariz, et al., 2013) did a study that showed a broad application of the Franki piles.
These areas include bridges, long rise buildings, docks and industrial buildings.

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References
Mariz, R. N., Picchi, F. A. & Granja, A. D., 2013. Application Of Standardized Work In Franki
Piles Concrete Work. Fortaleza, Research Gate.
Coduto, D. P., 2001. Foundation Design Principles and Practice. 2nd ed. London: Prentice Hall.
Day, R. W., 2006. Foundation Engineering Hadbook. 2nd ed. San Diego: McGraw Hill
Professional.
Fleming, K., Weltman, A. & Randolph, M., 2008. Piling Engineering. 3rd ed. New York: Taylor
and Francis.
FRANKI A Keller Company, 2018. Tallest Building In Africa Will Stand On Franki’s
Foundation. [Online]
Available at: https://www.franki.co.za/tallest-building-in-africa-will-stand-on-frankis-
foundation/
[Accessed 5 October 2018].
FRANKI Grundbau GmbH & Co. KG, 2010. FRANKI GROUNBAU. [Online]
Available at: http://www.frankifoundations.co.uk/franki-foundations
[Accessed 5 October 2018].
Rajapaske, R., 2008. Pile Design for Structural and Geotechinical Engineers. 1st ed. Burlington:
Butterworth-Heinneman Publications.
Venkatramaiah, C., 2006. Geotechnical Engineering. 3rd ed. Tirupati: New Age International
Limited Publisher.