Piles are essential foundation elements for marine structures like wharves and jetties, and driving them over water requires specialized methods. Several techniques have been developed for this purpose, taking into account factors such as cost-effectiveness and working conditions. These methods are specifically designed to enable the installation of piles in water, ensuring the stability and durability of marine structures.
Fig.1: Driving Piles Over Water
Methods of Driving Piles Over Water
Pile driving over water requires specific methods to be employed in order to ensure the stability and safety of the operation. Two common methods for pile driving over water include using a pile frame that is cantilevered from permanent piles, and utilizing a temporary false work trestle for support during the pile driving process.
In the first method, a pile frame is constructed that is cantilevered from permanent piles in the water. This frame provides a stable platform for the pile driver to operate from and ensures that the piles are driven vertically into the waterbed. This method is commonly used when there are existing permanent piles in the water that can be used as a base for the pile frame.
The second method involves the construction of a temporary false work trestle that is used to support the pile driver during the driving process. This trestle is built specifically for the project and is removed once the pile driving is complete. The use of a temporary trestle allows for greater flexibility in terms of location and can be used in areas where permanent piles are not available.
Another option for pile driving over water is the use of a floating pile driving plant. This method involves using a floating platform equipped with a pile driver that can be positioned in the water at the desired location. This method is often used for larger scale projects that require significant pile driving over water.
Regardless of the method chosen, pile driving over water requires careful planning and execution to ensure the safety of workers and the stability of the piles being driven.
Pile driving over water using pile frame cantilevered from permanent piles
The described method involves driving piles over water using a pile frame that is designed for this purpose. The pile frame is cantilevered out from piles that have been previously installed. The specific arrangement of the pile frame cantilevered from permanent piles is depicted in Figure-2.
Fig.2: Details of pile driving over water with cantilevered frame
One of the key benefits of using a cantilever pile frame technique for construction is its ability to remain unaffected by weather conditions, allowing work to continue even in adverse weather. However, this approach may not be cost-effective for large distances between piles. This is because progress would be slowed down due to the limited distance that the pile frame can cover. The frame is designed to work within a specific distance, and as such, the cantilever pile frame would only extend to a certain limit, restricting the space between piles. This limitation can impact the overall efficiency and speed of the construction work.
Pile driving over water from temporary false work trestle
In cases where a wharf structure is being built, there may arise a need for the construction of a large number of closely-spaced piles in shallow water. To address this challenge, an economical method has been developed which enables the efficient placement of these piles in such conditions. This technique offers a cost-effective solution that can be implemented without compromising the quality and durability of the structure being built. By leveraging this approach, construction teams can overcome the challenges presented by shallow water conditions and ensure the successful completion of the project.
Floating pile driving plant
A floating pile driving plant consists of a pile frame and a rectangular steel pontoon, with the pile frame fixed on one end of the pontoon. If a lightweight pile frame is used, conventional barges can be used for the work. However, if a heavy weight pile frame is used, a pontoon is required. To position the pontoon at a desired location precisely, two centrally placed double drum winches or four powered winches are used to warp it. The weight of the pile frame must be balanced for the pontoon to be stable, which is achieved by ballasting cells of the pontoon with water. Figure-3 displays the various components and configuration of a pile driven from a pontoon.
Fig.3: Pile driven frame fixed at one end of pontoon
Piles are transported by a barge to their installation positions, as shown in Figure-4 and Figure-5. To unload the piles, one end of the pile is lifted by sheaves located on the top of the frame. The other end of the pile is then tilted off the deck of the barge to allow the pile to swing freely and become vertical. Once the pile is in a vertical position, it is then arranged to the necessary 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
A single acting hydraulic or diesel hammer is considered the best option for driving piles, especially in unprotected working conditions from a floating plant. This type of hammer allows for accurate control of the blows and reduces the risk of damaging the piles. Additionally, fixing equipment with four jacked up legs on the barge can increase the stability of the barge against waves. By lowering the legs into the water, the barge can be lifted to avoid the impact of waves, creating a safer working environment. However, barges with jacked up legs are not suitable for use in deep water with a silt and clay sea bed. In Figure-6, a jack up barge is shown using a pile frame erected on the barge to drive piles into the sea bed.
Fig.6: Piles are installed from S 70 jack up barge, Newsland