2008.TEL.7289 Development of a Pile Anti Running Clamp
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Summary
Introduction to the problem
Structures are increasingly being built into the ocean. Main reason is the worldwide shortage of oil. Steel foundation piles are used to fix the structures into the ocean soil. These piles are sometimes driven into places where, due to the soil structure, it sometimes happens that the foundation pile starts to fall. The loss of a pile could cause that a project cannot be finished in time, resulting in great financial losses for the oil company.
Present concept: Pile Anti Running Clamp
IHC Handling Systems developed the Pile Anti Running Clamp (PARC) to stop a falling foundation pile. During pile driving the PARC is pulled around the foundation pile by means of the pre-tension. This relatively low hydraulic pressure in the clamp cylinders is controlled with an adjustable pressure relief valve. The pre-tension reduces the response time to the brake action, but also causes wear of the friction material. The human operator visually detects a falling foundation pile and starts the brake action. Thereafter oil is supplied to the cylinders to increase the hydraulic pressure and clamp the foundation pile, by which the pile is decelerated.
After deceleration of a foundation pile the friction material of the PARC turned out to be subjected to extreme wear. This report presents improvements to reduce the wear of the friction material.
Force distribution
During clamping large forces occur on several friction pads due to unequally distributed forces on the friction pads, which causes wear of the friction material. The force distribution has to be improved by the following changes of the PARC construction.
• Position cylinder connection points and hinges on the PARC construction’s neutral axis of the cross section.
• Increase the pile enclosure with friction pads by extending the row of friction pads.
In addition the calculation of the radial pad forces showed forces exceeding the maximum allowable force on the pads. Therefore the friction pads have to be enlarged.
Concept proposal: No-contact
2008.TEL.7289 Development of a Pile Anti Running Clamp
7
Reduction of the response time
To reduce the response time of the PARC, the response of the hydraulic system has to be reduced. The oil flow of the present hydraulic system is restricted by the valve which opens the oil flow from the accumulator. In addition this flow has to retract both clamp cylinders. Further the accumulator valve remains open when the accumulator is discharged. Consequently the accumulator is recharged simultaneously with the deceleration of the foundation pile. The response time of the hydraulic system is reduced by improving both hydraulic restrictions with the following adjustments.
• Dividing the hydraulic system in single systems for each clamp cylinder halves the required time to retract the cylinders.
• Closing the accumulator valve after discharge results in a faster hydraulic pressure increase and a decreased required time to decelerate the pile.
Simulation
The proposed design improvements are compared to the present PARC design performance by means of a simulation, which simulates the movement of a falling foundation pile. The simulation showed that the present PARC design depends on the response time of the operator and that the sensor considerably decreases the required time to decelerate a falling pile. If an additional valve is added to reduce the response time and the accumulator valve is closed, the no-contact concept decelerates the pile in a similar time as the present PARC design.
Conclusion
The following improvements are proposed:
• Adapt the PARC construction to improve the force distribution on the friction pads.
• Reduce the wear with the no-contact concept. This concept operates without contact during pile driving and includes a sensor to detect a falling foundation pile.
