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Top Down Basement Construction

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Andrew Pearce
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I am currently reviewing a project with a 250 000m3 basement 50% of which is below the water table. A secant pile wall is suggested as the perimeter solution, about 40% of the basement has an additional level of car parking the remainder is staorage or loading area. Above ground the building has a plan footprint of 35 000m2 with ground plus 2 levels of retail developemnt this is currently steel frame.

A top down solution using plunge columns has been suggested by the structural engineer. Reservations have been expressed here due to the large volume of excavated material to be disposed of.

Any observations, comments from fellow planners would be gratefully recieved.

Replies

Jonathan Kirby
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Andrew
I notice in another post that you say the basement is 8m deep with lowest 1m below the water table , but in this post its 50% below water i.e. 4m. ?? makes a huge difference to viable solutions.
with 4m of water and even with 1m a key problem will be heave and even boiling of the base of the excavation. Also once the base slab is in place uplift on the basement will be a major design problem.
To down for basements has tremendous programme advantages because once the groun level floor is in place and the piled foundations to the superstructure are in place then you can simmultaineously build the basement and the superstructure.
JK
Jaco Stadler
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Have you had a look at soil improvements. (Vibro Displacement)

Cheers
Jonathan Kirby
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Joined: 16 Jan 2005
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Andrew,
Given that you have to excavate the basement any way i wonder if the pile arrisings will add significantly to the total excavated volume.
please explain "plunge piles".
you could , if the ground is ok, use permanant sheet piles at the perimeter and or a balanced box design with props to reduce the piling depths.
JK