depth, the pile is inserted and either grout, granular material, or con- 

 crete is poured into the annulus. The tube is then withdrawn. While 

 withdrawing, the tube can also be used to compact the backfill material. 



The techniques and equipment for this system have been deployed 

 elsewhere. It is expected that the effort required to develop necessary 

 installation equipment and techniques for this system will be minimal. 

 However, the extent of improvement in its load carrying capacity require 

 further evaluation and confirmation. 



DISCUSSION 



General Pile Behavior 



The general behavior of piles in calcareous sands can be hypothesized 

 based on observations and engineering judgment. The driving energy in- 

 creased with increased cementation (Figure 14). Figure 36 is a plot of 

 the slopes of the curves from Figure 14. These six curves were combined 

 into two groups - a high and low void ratio. From Figure 36, the high 

 void ratio curve shows that as the silica content for a composition in- 

 creases, so did the energy required to drive the pile, indicating linear- 

 ity. The low void ratio curve did not indicate this with the amount of 

 data available. For the low void ratio, the driving energy did not in- 

 crease until the material composition was close to 100% silica sand. 

 This implies that the behavior of calcareous and silica sand compositions 

 is influenced by the presence of calcareous sand. 



More data will be needed to verify the behavior influence that cal- 

 careous sand plays in calcareous and silica sand compositions. Applying 

 some fundamental characteristics of shear strength in sand soils may 

 provide a preliminary explanation as to why calcareous sand can control 

 the behavior. From soil mechanics, we know that for strong particles in 

 an initially loose array that the array becomes denser during shear (Peck 

 et al. , 1974) . This occurs because during the application of shear the 

 particles move and assume a tighter array. If the array is tight, the 

 particles' grain-to-grain contact force will increase to a point where 

 grain overriding begins. At this point the array will experience volume 

 expansion provided the grains are strong and do not crush. The soil 

 mobilizes greater strength through grain overriding than by densif ication. 



In compositions of silica and calcareous sand, strong particles 

 (silica sand) and weak particles (calcareous sand) are blended together. 

 During pile driving, the shearing strength of the composition is mobi- 

 lized to resist the pile. For the dense compositions, the grain over- 

 riding, which normally occurs for mobilizing the strength, may not occur 

 due to the presence of the weaker grains. Where the strong silica sand 

 grains can support high contact pressures and transfer excessive pres- 

 sures to neighboring grains, this redundant loading array system breaks 

 down when the weak calcareous grains crush and leave a void and no 

 transfer of shear strength. With insufficient silica grain available to 

 provide an adequate transfer system, the composition behaves like a cal- 

 careous sand. 



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