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We are designing a US$400 million International Airport in Manila
Philippines.  The question I have is about the foundation system.

The building is a concrete flat plate slab system with drop panels.  The
level 1 (apron level) is also a structural flat plate slab system due to
the nature of the expansive soil conditions.  At the shear walls we have
pile caps with the range of 11m wide X 20m length and 1.5m in depth.  We
are running into conditions where we have to lower the top of the pile
caps by 2m to accommodate landscaping, HVAC, and electrical, and just
about everything else you can think of.  This means the shear walls will
pass through the slab to the top of the pile cap.   

The code section (1994) section "1807.2 Interconnection, under the note
Exception: other approved methods may be used where it can be
demonstrated that equivalent restraint can be provided".   We have used
this exception and eliminated tie beams because the flat plate slab at
this level is 300mm (12") thick.  

But now that at the shear walls/pile caps are 2m lower then the single
typical pile, due we need to provide some type of tie beam connections
to the structural slab, or due to the design of pile cap and pile group
action and the shear wall tying into the structural slab would this
action would adequate to provide the stability required.  Also the
caissons are into bedrock by 5m.

Thank you for any responses,

Thomas Long
Section Manager - PCI Asia