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Pile Caps vs Pile Raft

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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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