Deep Foundation

Chapter 1

POSITION OF PILING

Displacement piles

DISPLACEMENT PILES (DRIVEN PILES)

DISPLACEMENT PILES is

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Driven cast into used where the final length of pile is variable to be determined on site

Driven cast in – situ piles

Driven cast in – situ piles

Can be formed economically in diameters of 300mm to 600mm with lengths up to 18.00m designed to carry loads up to 1,300kN.

Require heavy piling rigs, an open level site and a site where noise is unrestricted.

There are 2 types of driven cast in – situ piles : permanent casing and temporary casing

a. Permanent casing

The permanent casing is usually formed with reinforced concrete shell

The shells are stacked over a steel mandrel, which has a special driving head, and a concrete shoe is placed at the foot of the bottom shell.

Typical Example :

West’s Shell Pile

WEST SHELL PILE1. The pile shells are

threaded on a steel mandrel, the diameter of which is slightly smaller than the internal diameter of the shell elements.

A steel band, acting as a sleeve, is installed at each shell joint. The internal face of each joint band is coated with mastic to prevent water penetration.

Finally, a pile shoe is fitted to the lower end of

the bottom shell.

WEST SHELL PILE

2. The whole assembly is then driven into the ground until the required depth is reached.

WEST SHELL PILE 3. Withdrawal of the

mandrel leaves a stable, water tight, hollow concrete column, at the base of which is an integral pile shoe

4. Steel reinforcement in the form of a prefabricated cage, is placed in the hollow core, which is then filled with concrete and compacted.

b. Temporary casing

A heavy steel casing is closed at the end with a plug of dry concrete.

The plug of concrete, driven with a drop hammer, expands, grip the sides of the casing and takes the casing into the ground.

On reaching the required depth the casing is restrained by cables and the plug of concrete is driven out into the ground to form a bulb at the end of the pipe

This bulb is often increased in size by a further batch of dry concrete.

One of the system known as Franki system.

b. Temporary casingThe cage or reinforcement is placed and the casing is

filled with concrete as the casing is withdrawn.

In some systems the casing is partially withdrawn and then re-driven.

This consolidates the concrete and forms a keyed surface at the soil face.

Most cast in – situ piles are constructed with high slump self-compacting concrete.

There some problem which can be encountered with this form of pile is necking due to ground water movement washing away some of the concrete thus reducing the effective diameter of pile shaft.

Typical example 1 : Franki Driven Insitu-Pile

Typical example 2 : Vibro cast insitu pile

PRE-FORMED PILES/PRECAST PILES These may be constructed using:

concrete, timber or steel.

a. Concrete preformed pilesThese are further sub divided

into : Normal reinforced concretePre-stressed concrete

These are used on medium to large contracts where soft soils overlying a firm strata are encountered

Length up to 12.00m with a section sizes ranging from 250mm x 250mm to 450mm x 450mm

These piles are percussion driven using a drop or single acting hammer

REINFORCED CONCRETE PILESPILING RIG

STORING OF PRECAST PILES ON SITE

PILING DRIVING SHOE

CONNECTION BETWEEN INTIAL PILES & EXTENSION PILES (FEMALE & MALE JOINT)

INITIAL PILES

EXTENSION PILES

a. Concrete preformed piles

Problems that can be encountered when using this form of pile in urban areas due to:

Transporting the complete length of pile through narrow and/or congested streets.

The driving process, which generally percussion, can set up unacceptable noise and/or vibrations

Many urban sites are in themselves restricted or congested thus making it difficult to manoeuvre the long pile lengths around the site.


Due to the problems listed above and the site difficulties, in recent years in favour of precast piles formed in segments of the partially preformed types of pile.

Typical examples of segmental types are West’s ‘Hardrive’ and ‘Segmental’ piles.


The ‘Segmental’ pile is designed for lighter loading conditions of up to 300kN.

It is formed by joining the 1.00m long standard lengths together with spigot and socket joints up to a maximum length of 15.00m.

Special half length head units are available to reduce wastage to a minimum.

WEST SEGMENTAL PILES

b. Timber preformed piles

These are usually of square sawn hardwood or softwood in lengths up to 12.00m with section sizes ranging from 225mm x 225mm to 600mm x 600mm.


Most timber piles are fitted with an iron or steel driving shoe and have an iron ring around the head to prevent splitting due to impact.


The pile is guided by a pile frame and driven by standard equipment such as drop hammer, which should be equal in weight to the pile being driven, for hard conditions, or half the pile weight in soft condition.

Load bearing capacities can be up to 350kN per pile depending upon section size and/or species.


Permanent piles should be cut off and capped with a reinforced concrete pile cap.

ADVANTAGES OF TIMBER PILES They are cheap and economical

Easily stored and transported without the aid of heavy equipment

Very useful when subsoil water is present

DISADVANTAGES OF TIMBER PILES

Timber piles deteriorate or decay very fast when subjected to alternate and drying. Hence it is essential to cut them below the water line can capped with concrete

Damage during over- driving Not very useful in hard, rocky strata Low structural strength

c. Steel preformed piles

Steel preformed piles can be formed in a wide variety of sections and can be adapted to suit almost any ground condition.

The most common types of steel pile are:

BoxTubeH-sectionScrew


Box piles

Box piles can be formed by welding or riveting sheet piles together or by producing purpose-made sections.

Three basic types are available: Larssen box piles, Frodingham box piles and Rendhex box piles.

BOX PILE & H SECTION


Box piles

Larssen box piles are formed by welding together two sheet pile sections with either continuous or intermittent welds.

Frodingham box piles are available in three different sections: standard box piles, plated box piles and double box piles.

The standard box piles are symmetrically in section and of constant wall thickness.


Box piles They are also welded together at the head and

toe to prevent movement during handling and driving.

If double box piles are used as individual units they should be intermittently welded over their length, as well as being riveted.


Box piles

Shoes or plates can be provided for all box piles and may be used to advantage when maximum resistance from a soft stratum is required or where ground heave is acceptable.

The head of pile is protected by a helmet, without a cushion packing between pile and helmet but including a dolly or packing between helmet and hammer.


Steel tube piles Steel tube piles are very similar to box piles in

principle.

The tube piles formation consist of welding a plate which has been formed into a continuous helix.

Automatic welding is used with two passes, one inside the tube, the other outside, which ensures full penetration of the weld through the thickness of the plate.


H-pilesH-piles or universal steel beams are

being increasingly used as bearing piles. They offer several important advantages such as:

Guaranteed integrity of the pile after driving

Ease of stacking and handling on siteIdeally suited to the support of heavy

axial loads and bending momentsSuitable for very hard driving and have

small displacement


H-piles

The piles may be driven by any type of hammer or vibrator, but must suit the angle of driving when driven on the rake.

Piles may be supplied coated with various forms of protective paint.


Screw piles Screw piles are a form of displacement pile in which

the shaft or cylinder is fitted at its lower end with a large diameter helical blade.

The piles are screwed into the ground by applying torque at the upper end of the pile shaft, which may be hollow or solid: hollow shaft piles are fitted with a square section head.

Screw piles have advantage over other piles in their uplift resistance in very soft ground and they also provide good resistance to lateral forces.

It is suitable for marine work and for other forms of construction where the sub-strata are very soft.

d. Composite piles

These are sometimes referred to as partially preformed piles and are formed by a method which combines the use of precast and in-situ concrete or steel and in-situ concrete.

They are used mainly on medium to large contracts where the presence of running water or very loose soils would render the use of bored or preformed piles as unsuitable.

Composite piles provide a pile of readily variable length made from easily transported short lengths.

Typical examples are ‘Prestcore’, West’s ‘Shell’

and cased piles.

d. Composite piles

The ‘Prestcore’ pile is a composite pile formed inside a lined, bored hole and is, strictly speaking, a replacement pile and is therefore described in more detail in the following section on replacement piles.

The ‘Shell’ pile is, however, a driven or displacement pile consisting of a series of precast shells threaded on to a mandrel and top driven to the required set.

After driving and removing the mandrel the hollow core can be inspected, a cage of reinforcement can be inserted and the void filled with in-situ concrete.

BSP PRESTCORE BORED PILE

d. Composite piles

Piles formed in this manner solve many of the problems encountered with waterlogged and soft substrata by:

Being readily adaptable in length, the shaft can be inspected internally before the in-situ concrete is introduced,

The flow of water or soil into the pile is eliminated The presence corrosive conditions in the soil can be

overcome by using special cements in the shell construction.

Typical Example : BSP CASED PILE

d. Composite pilesBSP cased piles

Typical composite piles using steel and in-situ concrete.

Cased piles are bearing piles consisting of a driven tube which is filled with in-situ concrete.

The casing manufactured from steel strip or plate which is formed into a continuous helix with the adjoining edges butt welded.

They are usually driven into position by using an internal drop hammer operating within the casing.

Self assessment

Suggest and sketch one type of pile that suitable to be used for a construction of the house on a reclaimed site.

(15 marks)

There is a bus with 7 girls inside,Each girl has 7 bags,Inside each bag, there are 7 Big cats,

Each Big cat has 7 small cats, All cats have 4 Legs each! Question: How many Legs are there inside the bus?

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