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Mr. D.R.R. Dick (F) (Past-President) : I think the authors are to be congratulated on their very interesting paper, particularly those parts where they relate their practical experience to future actions.
Professor N. Simons: Being a foundation engineer I obviously found a great deal of interest in the paper. but I would like to discuss one point in particular this evening and this is this philosophy of the design of a piled raft about which the authors have written. Considering raft foundations in the London clay, which are also piled, in many cases the piles are provided solely to reduce settlement. In other words, if there were no piles whatsoever, there would be a perfectly adequate factor of safety against failure. So when such piles are installed only to reduce settlement then obviously the design concept must be considered. The point I wish to make is; should the piles be designed to carry the total building weight, or is it necessary only to carry the net increase in loading on the piles?
Mr. C. W. Brown (M), Freeman Fox & Partners: The phenomenon of shear lag is one that until recently has been at best imperfectly understood. Manual methods of estimating its effect were very complicated to apply and were applicable only to highly idealised cross sections and loading conditions. Certain simplified empirical rules were proposed in some Codes, but the authors' paper describes the first real attempt to provide comprenehsive but comparatively simple rules. This, of course, has only been made possible by the availability of powerful finite element computer programs, and the authors deserve great credit for their presentation of a vast amount of information in four straightforward Tables (7(a) to (d)).