Driven piles are vastly used in offshore structures for which adequate prediction of bearing capacity is of great Importance. A case study is presented here on the application of dynamic pile testing to bearing capacity determination of a pile embedded in loose to compact sand and silt layers. The possibility of liquefaction of the loose layers as a result of cyclic loads such as earthquake, and therefore, reduction in shaft resistance of the pile are investigated. The Pile Driving Analyzer (PDA) was used for dynamic testing of the pile during driving by the hammer. The data was then further evaluated by the rigorous numerical analysis program CAPWAP to determine the static bearing capacity, and to distinguish between the tip resistance and the distribution of the shaft resistance along the pile. The results at the end of driving and also after a 30-minute wait indicated that the shaft resistance had gained an additional strength of 42% as a result of soil set up.
Piles are vertical or slightly inclined, relatively slender structural foundation members (Fellenins 1990). They transmit loads from the superstructure to the soil layers. Design of pile foundations consists of three parts: bearing capacity, strength of the pile material, and settlement requirements. Bearing capacity or ultimate load of a pile consists of a combination of shaft and tip resistance that develop in response to axial loading. Design for capacity consists of determining the allowable load on the pile by dividing the capacity with a factor of safety. Adequate determination of bearing capacity of pile foundations plays an important role in the safety, cost-effectiveness, and reliability of such systems. The bearing capacity is often difficult to assess even by means of a static loading test.
