Pile Driving Equipment

As discussed earlier piles are generally classified as bored piles or driven piles depending on the method of installation. Only driven piles are to be installed by driving using an equipment. Bored piles are installed after making a hole in the ground and inserting a cage of reinforcement followed by concreting. In some cases reinforcement is not provided.

Driven piles are made out of some materials like wood, concrete, steel and sometimes with composite section of wood and steel, wood and concrete or steel and concrete. They are manufactured in special lengths.

Sheet piles, as discussed earlier, may be wood, concrete or steel. These piles are also driven.

1. Process of Pile Driving

The process of pile driving consists of lifting the pile into position, holding it and driving it to refusal or a desired depth. In this exercise, long piles need to be cut to the required length and the short piles need to be extended for safe and economical driving operations, proper judgement, experience and the combined skill of the crew. Driving of sheet piles greatly affect the seepage of the ground water and thereby pose special problem. As a guide to decide the depth of penetration pile driving formula is used.

2. Components of Equipment

Pile driving equipment comprises of the following components (Chellis, 1951):

1. Driving Rigs
2. Guiding leaders
3. Pile hammer with Accessories
4. Additional aids for pre-boring and jetting
5. Boiler for steam raising or air compressor

(i) Driving Rigs

Driving rig provides basic operations of lifting the pile, holding the pile in position, hammering it into the ground or of pulling it out of the ground and guiding the pile in the desired direction of movement. The rig supports the boom and winch mechanism, driving hammer, the guiding leaders, and a platform for mounting of auxiliary equipment such as a jet pump, drilling auger steam boiler or air compressor.

(ii) Guiding Leaders

The leaders guide the pile and the hammer during operation which extends to the entire height of the rig. In case of piles to be driven below the level of the rig into excavations, trencher or water, telescopic or extensible leaders can be used. The leader should enable the hammer to deliver blows axially to the pile.

During the process of driving, the driving rig should be strong and stable. In case a boom is used, adequate space should be available between the pile top and the point for the hammer to work.

There are two types of rigs, viz., skid-mounted and crane-mounted. The skin-mounted rigs are provided with rail wheels or with long steel rollers for movement. The crane mounted rigs are mounted with a crawler or a truck chassis with a swinging deck. In the case of floating pile driving, both the rigs can be mounted on a barge.

(iii) Driving Hammers

Pile driving hammers impart energy required to drive the pile into the soil. The routinely used pile hammers work by hitting the pile on its head. The vibratory and sonic type of hammers are the two new types.

Hammers are classified as follows:

1. Drop hammers
2. Single-acting hammers
3. Double-acting hammers
4. Differential-acting hammers
5. Diesel hammers
6. Hydraulic hammers
7. Vibratory hammers
8. Sonic hammers.

Out of these hammers drop hammer and single-acting hammer are generally used which are explained below. For details of other hammers reference may be made to Purushothama Raj (2015).

1. Drop Hammer: This is the simplest form of hammer which does not use any external sources of power. The only mechanism needed is to lift the hammer through a cable. Although the process is slower, it is more efficient as it uses only the gravity. The drop hammer is basically a block of suitably shaped cast-iron with its centre of gravity centred near the base in order to facilitate smoothness of fall.
2. Singe Acting Hammer: The functioning of single acting hammer differs from drop hammer only in the manner of lifting of the ram after each blow. A conventional single acting hammer employs a piston connected to a ram at its bottom end and moving inside a cylinder. The hammer may be of an open type or closed type. Steam power or compressed air is used in the single acting hammer wilthout any adjustment or alterations and the pressure remains unchanged. This pressure ranges from 5.6 to 10.5 kg per cm² and used depending on the size of the hammer and its weight. The operation of the single-acting hammer costs less compared to a double acting hammer but its speed is slower.