Offshore Oil & Gas Future Development

Have you ever experiencing Pile Refusal?

I myself haven’t encounter any pile refusal during my assignment offshore. But i have heard there it has happen twice for the past 3 years and recently this year somewhere in Sarawak water. There are 3 reasons (there might some more reason) contributing to Pile refusal.

• Set-up (non continuous driving > 24 hrs)
• Excessive soil strength. i.e. hitting boulder or inaccurate soil data.
• Inadequate hammer capacity during piling.

Below is Pile Driving Refusal definition/condition with reference to API (American Petroleum Institute).

12.5.6 Driven Pile Refusal

The definition of pile refusal is primarily for contractual purposes to define the point where pile driving with a particular hammer should be stopped and other methods instituted (such as drilling, jetting, or using a large hammer) and to prevent damage to the pile and hammer. The definition of refusal should also be adapted to the individual soil characteristics anticipated for the specific location. Refusal should be defined for all hammer sizes to be used and is contingent upon the hammer being operated at the pressure and rate recommended by the manufacturer.  The exact definition of refusal for a particular installation should be defined in the installation contact. An example (to be used only in the event that no other provisions are included in the installation contract) of such a definition is:

Pile driving refusal with a properly operating hammer is defined as the point where pile driving resistance exceeds either 300 blows per foot (0.3m) for five consecutive feet (1.5m) or 800 blows per foot (0.3m) of penetration. (This definition applies when the weight of the pile does not exceed four times the weight of the hammer ram. If the pile weight exceeds this, the above blow counts are increased proportionally, but in no case shall they exceed 800 blows for six inches (152 mm) of penetration).

If there has been a delay in pile driving operations for one hour or longer, the refusal criteria stated above shall not apply until the pile has been advanced at least one foot (0.3m) following the resumption of pile driving. However, in no case shall be blow count exceed 800 blows for six inches (152mm) of penetration.

In establishing the pile driving refusal criteria, the recommendations of the pile hammer manufacturer should be considered.

Copyright by American Petroleum Institute. (www.API.org)

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