Existing pile driving theories for Gulf of Mexico soils do not always lead to satisfaction results. Certainly at large penetrations and in and beyond sand layers the predictions are poor. In view of the growing demands for accurate Drive ability predict ions an improved theory has been developed based on 1aboratory tests and post-analysis of case histories. The results are surprising. In clay the wall friction can be described by a reversible process of friction loss during driving and set-up during rest. In intermittent sand 1ayers the wall friction appears to be lost after sufficient progression of the pile. The point resistance in sand is difficult to analyse, due to lack of adequate soil parameters.
Pile driving in the under-to-normally consolidated Gulf of Mexico clays has only seldom caused problems for driving piles to their design penetration. Probably this is the reason that after the revolutionary introduction of the wave equation theory by Smith! in 1962, and the extensive calibration of the many parameters involved in this model by Texas A & M University2 in 1968, a further detailing of the soil resistance during driving was mainly focused on other areas in the world with more adverse driving circumstances (North Sea). Yet most existing drive ability theories do not produce very accurate results for the Gulf of Mexico. Certainly at deep penetrations, and in and below sand layers they largely fail to deliver satisfying predictions.
The tendency towards larger platforms with deeper and heavier pile found at ions, and the employment of huge and expensive crane vessels make a careful analysis of the driving phase increasingly important. A carefully planned hammer utilisation may save a number of add-on welds, and gain several days time and cost on the installation schedule. It is in view of these aspects that the authors' company has developed an improved theory based on both drive ability-directed 1aboratory research and post-analysis of observed driving behaviour. Source for the 1atter was the extensive data bank of pile driving records, collected from over 120 Gulf of Mexico platform installations. The relationships for clay wall friction have been established from 1aboratory tests and a number of uninterrupted clay profiles. The resistance from intermittent sand layers has been isolated and interpreted by supposing the clay friction to be known.
Modern pile drive ability analysis is principally based on the use of the wave equation model. Most difficult aspect of this theory is the definition of the soil resistance during driving. Smith suggested, albeit with care, to use the ultimate bearing capacity as a basis for it. The dynamic augmentation, found by comparing wave equation resistances at the final permanent set to test load results on the same piles, was expressed in a damping relationship which was assumed linear to the velocity of the pile part (1 + J. v).
