Pile foundations are the part of a structure used to carry and transfer the load of the structure to the bearing ground located at some depth below ground surface. The main components of the foundation are the pile cap and the piles.

Piles are long and slender members which transfer the load to deeper soil or rock of high bearing capacity avoiding shallow soil of low bearing capacity The main types of materials used for piles are Wood, steel and concrete. Piles made from these materials are driven, drilled or jacked into the ground and connected to pile caps. Depending upon type of soil, pile material and load transmitting characteristic piles are classified accordingly. In the following chapter we learn about, classifications, functions and pros and cons of piles.

2- Historical

Pile foundations have been used as load carrying and load transferring systems for many years. In the early days of civilization, from the communication, defense or strategic point of view villages and towns were situated near to rivers and lakes. It was therefore important to strengthen the bearing ground with some form of piling.

Timber piles were driven in to the ground by hand or holes were dug and filled with amsand and stones. In 1740 Christoffoer Polhem invented pile driving equipment which resembled to days pile driving mechanism. Steel piles have been used since 1800 and concrete piles since about 1900. The industrial revolution brought about important changes to pile driving system through the invention of steam

and diesel driven machines. More recently, the growing need for housing and construction has forced authorities and development agencies to exploit lands with poor soil characteristics. This has led to the development and improved piles and pile driving systems. Today there are many advanced techniques of pile installation.

3- Function of piles

As with other types of foundations, the purpose of a pile foundations is:

to transmit a foundation load to a solid ground to resist vertical, lateral and uplift load A structure can be founded on piles if the soil immediately beneath its base does not have adequate bearing capacity. If the results of site investigation show that the shallow soil is unstable and weak or if the magnitude of the estimated settlement is not acceptable a pile foundation may become considered. Further, a cost estimate may indicate that a pile foundation may be cheaper than any other compared ground improvement costs.

In the cases of heavy constructions, it is likely that the bearing capacity of the shallow soil will not be satisfactory, and the construction should be built on pile foundations. Piles can also be used in normal ground conditions to resist horizontal loads. Piles are a convenient method of foundation for works over water, such as jetties or bridge piers.

4- Pile arrangement

Normally, pile foundations consist of pile cap and a group of piles. The pile cap distributes the applied load to the individual piles which, in turn,. transfer the load to the bearing ground. The individual piles are spaced and connected to the pile cap or tie beams and trimmed in order to connect the pile to the structure at cut-off level, and depending on the type of structure and eccentricity of the load, they can be arranged in different patterns. Figure 2.1 bellow illustrates the three basic formation of pile groups.

5- General types of single pile:

1- End bearing piles

2- Friction piles

3- Cohesion piles

4 -Steel piles

5 -Concrete piles

6- Pre-cast concrete piles

7- Timber piles (wood piles)

8- Others

6- General types of Group pile and bearing capacity of pile groups:

1-Pile group in cohesive soil

2- Pile groups in non-cohesive soil

3- Pile groups in sand

7- Our Pile Installation Methods:

1- Pile driving methods (displacement piles)

2- Drop hammers

3- Diesel hammers

4- Pile driving by vibrating

5-Boring methods (non-displacement piles)

6- Continuous Flight Auger (CFA)

7- Underreaming

8- C.H.P (Continuous helical displacement piles)

8- SCFW Load Test on Pile

Pile load test are usually carried out that one or some of the following reasons are fulfilled:

· To obtain back-figured soil data that will enable other piles to be designed.

· To confirm pile lengths and hence contract costs before the client is committed to over all job costs.

· To counter-check results from geotechnical and pile driving formulae

· To determine the load-settlement behaviour of a pile, especially in the region of the anticipated working load that the data can be used in prediction of group settlement.

· To verify structural soundness of the pile.

9- Test loading: There are four types of test loading:

1- compression test

2- uplift test

3- lateral-load test

4- torsion-load test

the most common types of test loading procedures are Constant rate of penetration (CRP) test and the maintained load test (MLT). CRP (constant rate of penetration) In the CRP (constant rate of penetration) method, test pile is jacked into the soil, the load being adjusted to give constant rate of downward movement to the pile. This is maintained until point of failure is reached. Failure of the pile is defined in to two ways that as the load at which the pile continues to move downward without further increase in load, or according to the BS, the load which the penetration reaches a value equal to one-tenth of the diameter of the pile at the base. In the cases of where compression tests are being carried out, the following methods are usually employed to apply the load or downward force on the pile:

A platform is constructed on the head of the pile on which a mass of heavy material, termed "kentledge" is placed. Or a bridge, carried on temporary supports, is constructed over the test pile and loaded with kentledge. The ram of a hydraulic jack, placed on the pile head, bears on a cross-head beneath the bridge beams, so that a total reaction equal to the weight of the bridge and its load may be obtained. MLT, the maintained increment load test, the maintained increment load test, kentledge or adjacent tension piles or soil anchors are used to provide a reaction for the test load applied by jacking(s) placed over the pile being tested. The load is increased in definite steps, and is sustained at each level of loading until all settlements has either stop or does not exceed a specified amount of in a certain given period of time.

SDC offers variety of soil tests, water tests, and land surveying associated with our construction sites, and for other general environmental purposes

For additional technical questions or comments about the content of this page Please, contact:

Sami Abdellatif Mohammed, Tel. + 249 9 1230-4459, or e-mail at: Sami@SudanDrill.com