Methods of Piling

Other Methods of Piling

1. Jetting Piles - water jetting may be used to aid penetration of a pile into a sand gravel stratum. It is ineffective infirm to stiff clay or soils containing much coarse gravel, cobbles or boulders.

2. Pile Driving by Vibration - vibratory methods of driving sheet piles or bearing piles best suited to sandy or gravelly soils. Pile driving vibrators consist of pair or exciters mounted on the vibrator unit, the motors of each pair rotating in opposite directions. The amplitude of vibrations is sufficient to break down the skin friction on the sides of the pile. Vibrators will drive steel piles through loose to medium dense sands and gravel with comparative ease, but there are likely to be difficulties with dense sands, where energy may be insufficient to displace the material to permit entry of the pile. Vibrators can also be used for extracting piles and are frequently used connection with large diameter bored and cast-in-place piling work for sinking and extracting pile casings.

3. Pile Driving over Water - piles for jetty or wharf structures built over can be driven from specially designed pile frames cantilevered out from the permanent piles already driven, from ordinary pile frames operating from temporary piled trestles, from jack-up barges or from floating plant.

4. Pile Driving through difficult ground - these methods include boring a hole sufficient diameter through the difficult ground to receive the pile. In loose ground, the hole may have to be cased which sometimes leads to difficulties with extraction of the casing. Another method is to drive a heavy steel spud or joist section through the ground and to drive the pile through the loosened soil left after withdrawing the spud. Another is through the use of diamond core drills.

5. Test Piling - whenever possible, test piles should be of the same type and dimensions as the permanent piles which are intended to be used. This is the only way to ensure that the designed penetration will be attained and that the designer's estimate of the safe working load can be checked when the piles are subjected to test loading.

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Pile Driving Equipment

Pile Driving Equipment

1. Piling Rigs. Piling Rigs consist of a set of leaders mounted on a standard crane base. The leaders consist of a stiff box or tubular member which carries and guides the hammer and the pile as it is driven into the ground. The leaders can be raked backwards and forwards by screw or hydraulic adjustment of the back stay and lower attachment to the base machine.

2. Piling Winches. Winches operating with pile frames mounted on barges or fixed stagings may be powered hydraulically or by steam, diesel pr petrol engines, or electric motor. Steam powered winches are commonly used where steam is also used for the piling hammer. Light winches may only have a single drum, but double and triple drum winches which can raise hammer and pile separately are more useful where speed of handling and driving is desirable. The winches may be fitted with reversing gears so that in addtion to their main purpose of lifting hammer and pile, they can also carry out the auxiliary function of the operating the raking, rotating and travelling gear.

3. Hanging Leaders. Hanging leaders are designed for suspension from the jib of a crane or excavator. A steel strut, capable of adjustment in lengths, forms a rigid attachment from the foot of the leaders to the bed-frame of the machine.

4. Hammer Leaders. In situation where it is desirable to dispense wholly with piling frames or hanging leader, hammer guides or rope-suspended leaders can be attached to the piles and the latter are guided by timber or steel frameworks.

5. Piling Hammers. The selection of suitable hammer for a piling project depends on a number of factors including the size and weight of the pile. The driving resistance which has to be overcome to achieve the design penetration, the available space and headroom on the site and the availability of the cranes and the noise restrictions which may be in force in the locality.

6. Helmet, driving cap, dolly and packing

A steel helmet is placed over the top of the concrete pile in order to hold the resilient dolly packing which are interposed between the hammer and the pile to prevent shattering of the latter at the head.

The dolly is placed in a square recess in the top of the helmet. It is square at the base and rounded at the top. Elm dollies are used for easy to moderate driving and for hard driving a hardwood. Plastic dollies car, withstand much heavier driving than timber dollies.

Packing is placed between the helmet and the top of the pile to cushion the blow between the two. Various types of material are used such as hessian and paper sacking, thin timber sheets, coconut matting, saw dusts in bags and wall  board.

Driving caps are used to protect the heads of steel bearing piles. They are especially shaped to receive the particular type of pile to be driven and are fitted with recess for a hardwood or plastic dolly and with steel wedges to keep the caps tight on the pile. A cheap from of cushioning consists of scrap wire rope in coils or in the form of short pieces of laid cross-wise in two layers.

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Piles

Piles

Piles are used to transmit foundation loads through strata of low bearing capacity to deeper soil or rock strata having a high bearing capacity. Piled are also used in normal ground condition to resist heavy uplift forces or in poor soil condition to resist horizontal loads. Piles are convenient method of foundation construction works over water such as bridge piers or jetties.

Classification of Piles

Piles are classsified according to their carrying capacity,

1. End-bearing Piles - carrying capacity derived from toe of the piles.

2. Friction Piles - are piles which derive their carrying capacity by skin friction or adhesion. the piles do not reach an impenetrable stratum but are driven for some distance into a penetrable soil.

Types of Piles

1. Driven Piles - preformed units such as timber, concrete, steel, driven into the soil by the blows of a hammer.

2. Driven and Cast-in-place Piles - formed by driving a tube with a closed end into the soil and filling ethe tube with concrete. The tube may or may not be withdrawn.

3. Jacked Piles - steel or concrete units jacked into the soil.

4. Bored and Cast-in-place Piles - piles formed by boring hole into the soil and filling it with concrete.

5.  Composite Piles - combination of two or more of the preceding types, or a combination of different materials in the same type of pile.

Considerations in the Selection of Piles

1. Location and type of structure
2. Ground conditions
3. Durability
4. Final selection is made from considerations of overall cost.

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