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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] ------------------------------------------------------------- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%