Based on these observations, it appeared that pile driving resis- 

 tance may not be a rational parameter for use in pullout capacity (or 

 frictional pile capacity) predictions for piles in calcareous sands. 



As described earlier, subsamples of the soil samples were taken at 

 various depths and distances from the pile wall after each pullout test. 

 The fines content versus distance from the pile wall (soil-pile inter- 

 face) are presented in Table 8. These results show that most of the 

 grain crushing took place at or near the pile wall. The degree of grain 

 crushing decreased away from the pile wall. The grain size analyses for 

 the specimens show that: 



1. At or near the pile wall, more grain crushing occurred along 

 the bottom 8 inches of the pile than the top 4 inches. 



2. Pile driving crushes more grains of the higher density calcar- 

 eous sand samples while its effect on silica sand and lower 

 density calcareous sand samples was less pronounced. 



The observation in item I appears questionable since one would think 

 that grain crushing would be more pronounced near the soil surface where 

 more shear stress cycles are imposed by the pile driving. This could be 

 caused by the physical limitation of the red barrel and pressurization 

 system. The top 4 inches of the pile were subjected to less complete 

 confinement than the bottom 8 inches of the pile, thus, it can be hypoth- 

 esized that grain crushing also depends on the applied confining stress. 



ALTERNATIVE PILE CONCEPTS 



In the past, the most popular piles used in calcareous sand have 

 been the open-ended pipe piles. The reasons for this were discussed in 

 the BACKGROUND section. However, it has been hypothesized that driven 

 pipe-piles create problems in calcareous sand, particularly in regard to 

 developing skin resistance. These hypotheses have been verified by ERTEC, 

 1983a. The recognized problems do not rule out the use of pipe piles, 

 but other piling concepts might be more appropriate for some cases. 



ERTEC was funded to investigate the possibility of using alternative 

 piling systems that could be used in calcareous soils. Conceptual sys- 

 tems were developed on the basis of the current understanding of the 

 pile behavior in calcareous sands. Because the behavior of piles in 

 calcareous sands is complex and the understanding meager, it was neces- 

 sary to postulate various behavioral aspects on the basis of engineering 

 understanding and judgment. Attempts were made to extend beyond the 

 state-of-the-art, thus, some of the developed systems involve substantial 

 risks and require development work in order to prove their viability. 



In developing the improved piling systems for calcareous sediment 

 applications, the following principles were considered: 



1. Recognized the various special behavioral aspects of piles in 

 calcareous soils based on our knowledge. 



2. Postulated the mechanisms behind these aspects in accordance 

 with good engineering judgment and assumptions if the knowledge 

 was nonexistent. 



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