mechanical systems. Explosives can also be used to force the pile shaft 

 to expand outward and key into the sediments and cavities. Another method 

 would be to design the pile with weak segments that are expanded by exces- 

 sive drilling forces. 



Alternate A . For this system, the structural integrity of piles 

 during installation, pressurization, and loading has to be carefully 

 considered in the design. 



The above PP alternates are unconventional. Development work is 

 needed in pile design, installation procedures, and confirmation of their 

 load carrying capacity. The first alternate involves installing an ex- 

 pandable pile consisting of two overlapping half sections as shown in 

 Figure 28. The pile could be installed by using either impact hammers 

 or drilling and inserting. Hydraulic pressure or mechanical systems can 

 be used to force the pile to expand outward. There are a number of sys- 

 tems that can be designed for this purpose. The criteria for selecting 

 the correct system should be based on cost and complexity of the applica- 

 tions. Two sample mechanical systems are shown in Figure 28; one system 

 expands the pile by applying a vertical downward force and the second 

 system by applying a torsional force. 



Alternate B. The second alternate (Figure 29) involves using explo- 

 sive charges at regular intervals and locations where cavities are adja- 

 cent to the pile shaft. A regular, tubular steel pile (either open-ended 

 or close-ended) can be used. After the pile is installed, the explosive 

 is detonated. (A special pile cap may be required to maximize the 

 blasting effect.) Exploding the pile will expand the wall and cause it 

 to fill the voids or cavities. This system will increase the lateral 

 pressure on the pile shaft as well as create spurring contacts with the 

 cavity walls when the pile is subjected to axial compression or uplift 

 (i.e., increase the skin friction resistance). 



Alternate C . This alternate involves installing specially designed 

 and fabricated, open-ended piles that have segments of weak sections (by 

 slotting the piles or using thinner wall thickness) as shown in Figure 30. 

 The piles can be installed by impact hammers or drilling and inserting 

 procedures. If impact hammers are used, it is important to ensure that 

 the impact energy is strong to install the pile to the proper depth, but 

 will not damage the weaker segments (section) of the pile. After the 

 pile has been installed, a higher impact energy is used to buckle the 

 weaker segments and force them to fill any voids or cavities. 



Backfilled and Pressurized Piles (BPP) 



This system combines the backfilling procedures discussed above 

 with the pressurized pile technique. The oversize hole would be drilled 

 and backfilled. The expandable pile would then expand against the newly 

 placed backfill. 



22 



