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Re: Pile Caps vs Pile Raft

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Mam,

From your client's point of view the three most important considerations are
1.) Cost,
2.) Cost, and
3.) Cost.
On that basis your most favorable choice is Option 2.

Regards,

H. Daryl Richardson

----- Original Message ----- From: "MAM" <mam(--nospam--at)cyber.net.pk>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, August 23, 2006 9:55 AM
Subject: Pile Caps vs Pile Raft


Members' comments solicited on the following issue:
50 story building  with two basements; Seismic zone 2B (UBC);
Columns at 9.0m grids each direction;
1200/1500 mm dia bored piles drilled in weathered rock (25%RQD) with 4 piles under each column ; Ground water level 1.0 m below surface; Option 1: Provide a continuous pile raft ( 3000 mm thick) over the entire area, Option 2: Provide individual pile caps under each column, capping a set of 4 piles and inter-connecting the pile caps with tie-beams along column centerlines with a 300mm thick monolithic slab on top (actually extension of the upper 300mm of the pile cap thickness) to cover the entire area upto the basement retaining walls. Option 1 will be very costly in terms of concrete and steel ( tremendous quantity of continuous concrete pour required), while option 2 will not only be much cheaper but also would be very convenient to construct, pile cap to pile cap with a horizontal
construction joint just 300mm below the pile cap top .
Of course all the requirements of equilibrium and stability would be fullfilled alongwith
water-proofing.
My question: What are the merits and demerits of  each of the options?
Why not go with option 2 if it fulfils all the code requirements?
Your comments would be greatly appreciated.
Thanks,
mam



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