Various methods have been developed to drive piles over water. Piles are used as a foundation for various marine structures such as wharves and jetties. These piles need to be driven over water.
The methods of driving piles over water along with their economy and suitable working condition are discussed.
Fig.1: Driving Piles Over Water
Methods of Driving Piles Over Water
Pile driven methods over water include:
- Pile driving over water using pile frame cantilevered from permanent piles
- Pile driving over water from temporary false work trestle
- Floating pile driving plant
Pile driving over water using pile frame cantilevered from permanent piles
In this method, piles are driven over water from a specifically designed pile frame that is cantilevered out from piles that have been installed in advance. The details of arrangements of pile frame cantilevered from permanent piles is provided in Figure-2.
Fig.2: Details of pile driving over water with cantilevered frame
The most outstanding advantage of this technique is that weather condition will not affect the progress of the work. However, it will not be a cost-effective method if the distance between piles are large. This is because the progression of the work would be restricted and slow, and the pile frame is commonly designed to a specific distance.
So, the cantilever pile frame would extend to a limit distance and hence it restricts the space between piles.
Pile driving over water from temporary false work trestle
This technique is an economical method to place large number of closed spaced piles in shallow water. This construction condition might be encountered when wharf structure is constructed.
Floating pile driving plant
Floating pile driving plant is composed of a pile frame fixed on one end of a rectangular steel pontoon. If lightweight pile frame is used, then conventional barges can be used to carry out the work.
However, if heavy weight pile frame is used, then a pontoon is utilized. Two centrally placed double drum winches or four powered winches are used to warp the pontoon into its passion. These winches help to position the pontoon at a desired location precisely.
Moreover, it is required to balance the weight of the pile frame for the pontoon to have adequate stability. This can be obtained by ballasting cells of the pontoon with water.
Figure-3 shows different component and configuration of a pile driven from a pontoon.
Fig.3: Pile driven frame fixed at one end of pontoon
Piles are loaded on a barge which delivers them to the installation positions as it may be observed from Figure-4 and Figure-5.
One end of the pile is lifted by sheaves on the top of the frame and the other end is canted off the deck of the barge to make the pile swing freely into a vertical position from where it is arranged to the required height in the leaders.
Fig.4: Piles are brought to the installation points using barges alongside the pontoon
Fig.5: Driving piles from pile frame operating one pontoon accompanied by a barge that deliver piles
The most desired hammer for driving piles is claimed to be single acting hydraulic or diesel hammer which is considerably suitable to operate on from floating plant in unprotected working condition.
Not only do the blows of such hammer can be controlled with significant accuracy but also the level of damaging piles would be declined substantially. Furthermore, the stability of barges against waves can be increased by fixing equipment, which is equipped with four jacked up legs, on the barge.
The legs can be lowered into water and the barge can be lifted to avoid the effect of water waves and consequently achieve safer working condition in unprotected working conditions.
Barges with jacked up legs cannot be used in considerably deep water with silt and clay sea bed. Figure-6 show type of jack up barge that driven pile into the sea bed from a pile frame erected on the barge.
Fig.6: Piles are installed from S 70 jack up barge, Newsland