These concepts are different from conventional piling systems to a 

 varying extent and were evaluated on the basis of the limited under- 

 standing presently possessed, various postulations regarding calcareous 

 soil-pile interaction, and engineering judgment. These concepts and 

 their effectiveness of improving load carrying capacity in calcareous 

 sediments still need to be proven. In addition, most of the procedures 

 and equipment required for deploying these "improved" piling systems 

 need further development. Some of the piling systems are presented with 

 various alternates depending on site conditions and applications. 



Backfilled Piles (BP) 



As shown in Figures 24 through 26, this system installs the pile in 

 an oversized hole and then backfills the annulus between the pile and 

 the hole with granular material. The granular material can be densified 

 by internal underwater vibrators or by vibration force provided from the 

 pile top or by other means. This procedure is very similar to the 

 drilled and grouted piles except granular material is used instead of 

 grout. 



Using granular material as backfill offers the following advantages: 



1. Increases the effective lateral stress on the pile shaft, thus, 

 increasing the skin friction resistance. 



2. Eliminates grain crushing and soil arching effect in the cal- 

 careous sands. 



3. Fills the cavities with granular material. 



4. Eliminates the need for grout. 



The major disadvantages are: (1) Granular material must be quarried 

 and placed underwater, and (2) drilling equipment must be used to drill 

 the oversized hole. There are several alternates that are capable of 

 drilling an oversized hole. They are described as follows: 



Alternate A - Conventional Drilling . This alternate is shown in 

 Figure 24. The oversized hole can be drilled by conventional drilling 

 techniques. For noncemented or lightly cemented calcareous soils, dril- 

 ling mud may be required to stabilize the drill hole. In this case, a 

 granular material, such as sand slurry, can be pumped in under pressure 

 to force out the drilling mud. 



Further research and development work is necessary for this alter- 

 nate. This includes determining: 



• The types of granular materials suitable for use as backfill. 



• The extent of mud contamination and its effect on the granular 

 backfill and pile capacity. 



• Procedures and equipment needed to place and compact the granular 

 material. 



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