The overriding considerations in foundation design are an adequate factor of safety against catastrophic failure, and that total and differential settlements should not affect the functional performance of the structure.2. As a general principle, depending of course on the soils encountered, it is preferable to transfer heavy loads downwards rather than spread them at a higher level by increasing the area of foundation outwards. For the NatWest Tower the loading intensity on the plan area was in excess of 12 t/ft2 (1200 kN/m2) which is far more than London Clay can take.3. In choosing appropriate values of the soils properties, no matter how accurate the results of the site investigation may have been, it has to be remembered that soils are natural materials, subject to considerable variations within quite short distances, and whose engineering properties can change unpredictably after a load has been applied. For these reasons, calculations of settlement, however sophisticated they may claim to be, should be taken with a margin of f 1&25%. In the event, conventional settlement analyses using the Skempton-Bjerrum method based on Terzaghi, differed from finite element analyses by about 5-10%, and by about the same amount from measured values. Some of this last relationship can be explained by differences between theoretical and actual loadings.Professor J. E. Gibson, The City University 6. At the City University we were involved in carrying out tests on the models shown in Figs 17 and 19 of Paper 8673. These tests were to be used to support and verify the design analysis of the main core of the tower. Owing to the complicated Papers published: Proc. Instn Ciu. Engrs, Part 1,1983,74, Aug., 387494. 389 Downloaded by [ RICE UNIVERSITY] on [11/09/16].

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