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[Q]: Seismic bearing capacity of dense saturated sand ...

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Peter

My guess is that you don't have a problem.

First establish with your geotechnical engineer that under this loading the
footings will not sink into the ground.

Make sure that your foundation is tied together so it doesn't get pulled
apart by different parts of the foundation trying to go in different
directions.

Given these assumptions you may find that nature has conspired to act as a
base isolation system for your building in which case count yourself lucky.
 Since you may prefer that the isolation occurs in the ground and not at
the soil structure interface, determine the maximum acceleration the ground
can deliver to your foundation and provide keys or other mechanism to keep
the building from sliding at that force level.  On the other hand if you
can accept the damage you might allow it to slide at the building
foundation interface.

Mark Gilligan


___________________________________________

Message text written by INTERNET:seaint(--nospam--at)seaint.org
>
Hi,

The problem I have is concerning the seismic design of shallow
foundations under following conditions:

1. thick layer of very dense sand,
2. ground water table as high as the ground surface
3. very high seismic loading, ca. 0.4 g
4. foundation size, ca. 10 x 10 m

************ What I know:

Since the soil is dense, I think it may not be susceptible to
liquefaction and liquefaction calculation is not necessary.

However, the EQ waves will develop inertia forces within the soil volume,
which will be equilibrated by dynamic stresses (mainly horizontal shear
stresses).
These stresses mobilize a fraction of the available soil strength and
consequently the strength available to balance the inertia forces arising
from the superstructure
is not necessarily the full soil strength. As an extreme case, when the
ground acceleration,
at a given depth, is too high, the induced seismic stresses are limited by
the soil strength
(called dynamic fluidization).
Hence, for very high ground accelerations, no equilibrium can be reached,
even in the absence
of a foundation ! 

*********************What I do not know:

I cannot find any word in the codes about this problem !

In this regard, what is the seismic design calculation procedure for
shallow
foundations on saturated dense sand
according to the most recent US codes ?

Could you recommend some publications ?

I would be very thankful to you if you could help me with some information.

Best regards,
Peter Rangelow
Frankfurt, Germany<