• The best size of the backfilled annulus to minimize the effects 

 of soil arching on the lateral stress. 



• The pile behavior under static and cyclic loadings. 



From a construction viewpoint this system is applicable with cemented 

 or solidified calcareous sediments, where the drilled hole will stay 

 open without using drilling mud. Installing piles under these conditions 

 would be relatively simple and straightforward. 



Alternate B - Cased Drill Hole Using a Withdrawal Tube . Contamina- 

 tion by drilling mud can reduce the load carrying capacity significantly. 

 To avoid this complication, an alternative, which eliminates the need 

 for drilling mud, is needed. This alternate (Figure 25) involves at- 

 taching a drill bit to the tip of a withdrawable tube slightly smaller 

 than the oversized drilled hole. The drill bit and tube are advanced 

 until the correct depth is reached. The drill bit is then withdrawn 

 while holding the tube stationary followed by inserting the pile using a 

 centralizer. Granular material is placed (or pumped in) into the annulus 

 between the pile and the wall of the oversized hole. The tube is slowly 

 withdrawn during backfilling and used to compact the granular material 

 at regular intervals. Installation is completed when the tube is fully 

 withdrawn. 



Alternate C - Driving a Withdrawal Tube With an Expendable End Plate . 

 This alternate is similar to Alternate B except the oversized hole is 

 created by driving a withdrawal tube with an expendable end plate attach- 

 ment (Figure 26) . After the tube is driven to the correct depth the 

 pile is inserted. Backfilling and compacting are done by following the 

 same procedures as those described for Alternate B. 



The development work required for Alternates B and C are similar to 

 those described for Alternate A except for the problem of contamination. 



Vibratory-Installed Backfilled Piles (VBP) 



This system can also be used to avoid using drilling mud in nonce- 

 mented and lightly cemented calcareous sediments. As shown in Figure 27, 

 this system installs of an inverted and slightly tapered pile using vi- 

 bratory hammers. The gap between the tapered piles and hole created by 

 the pile tip can be filled with granular material from a supply reservoir 

 or pumping in granular (sand) slurry. Vibratory hammers are used to 

 drive the piles and compact the backfill materials at the same time. 



Again, the procedures and equipment to install this system require 

 further development. However, the effort is expected to be minimal. 

 Further development work as described for the BP system (except for the 

 drilling mud problem) is also needed. 



Pressurized Piles (PP) 



This system uses artificial imposition of a high lateral stresses 

 on the pile shaft. This can be done in several ways. One method would 

 be to use split-designed piles that can be expanded through hydraulic or 



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