Dear Henk van der Velden
There do not appear to be many records of the swelling behaviour of
clays at the base of deep excavations where there is both piezometric
data and movement records. We were involved in monitoring
heavily over-consolidated Gault clay beneath a 10m deep excavation at
Lion Yard in Cambridge some years ago and we were able to derive the
field swell stress-strain relationship from the expensometer and
piezometer data. Due to the non-linearity of this relationship the
negative pore pressures just below the excavation (remote from the
drained boundary) changed very much quicker that you would expect from
application of conventional theory. Thus the effective stresses in the
clay there dropped quickly. The results of this aspect of the
monitoring work are written up in the paper:
Observed heave and swelling beneath a deep excavation in Gault clay.
by Nash, D.F.T., Lings, M.L. and Ng, C.W.W. (1996). in International
Symposium on Geotechnical Aspects of Underground Construction in Soft
Ground. (Balkema)
I appreciate that some of the findings may not be directly applicable
to lightly over-consolidated clay but I hope it helps.
Best wishes.
David Nash
On Fri, 08 Jan 1999 15:01:08 +0100 [log in to unmask] wrote:
>
> Dear all,
>
> In december I posed a question in this mailbase on the time-dependant
> swelling behaviour of clay. I got one answer on this question. I'll try it
> again now, maybe the question is more clear.
>
> I am looking for some information on the time dependant rebound behavior
> (due to deep excavatioin) of lightly over consolidated clays. I am
> particularly interested in how shear strength decreases/develops with time
> from the moment of unloading to the end of construction. I want to find out
> if timing the construction during and after a 40 meter deep excavation in
> Amsterdam is of significance.
>
> Who can give me some information on this subject?
>
> Yours faithfully,
>
> Henk van der Velden
> the Netherlands
-------------------------------------------------------------
David Nash Phone Office: +44 (0)117 928 7714
Dept. Civil Engineering Secretary: +44 (0)117 928 7708
University of Bristol Fax: +44 (0)117 928 7783
Bristol BS8 1TR, UK [log in to unmask]
-------------------------------------------------------------
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|