Cive3014 Construction | Construction Of Assessment Answers

Answer:

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shift the soil when they are being pushed into the ground while Non-displacement piles are those that the steel case is withdrawn after concreting of which examples include Alpha piles and vibrex piles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)

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.

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

(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.

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.
   
   
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.

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.

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: https://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.