COMPUTER INTERACTIVE PROPORTIONING OF FOOTINGS

Abstract

The allowable bearing pressure, based on which the foundations are proportioned, is dependent on the soil type, dimension's of the foundation, the stiffness of the soil and its variation with depth and many other factors such as position of water table, permissible settlement •etc. Thus the method' of proportioning of foundation is a method of trials. Moreover, a number of methods are available for proportioning of foundations resting on sand. Therefore, to facilitate an easy and efficient solution of the problem, a computer program. has been developed for proportioning of foundations on sands and on clays. • •The computer program processes the data usually •obtained from field tests such as standard penetration test, plate load test and static cone penetration test for the case of footings on sands and laboratory test 'such as consolidation test and shear test and makes use of the same for proportioning of footings using methods currently adopted in practice. The program is of interactive type and helps the designer by providing necessary guidelines, if needed. The program is used to analyse some actual field/laboratory test data for proportioning of footings. Also, some assumed data are analysed to make a parametric study such as the effect of variation of soil stiffness with depth on settlement, effect of layer thickness on the computed consolidation settlement of foundations on clays etc. It is observed from the results that the Schmertmann's method based on static cone penetration test data and the method based on standard penetration test data give contradictory trends of ,computed settlements obtained as a function of width. For footings of narrow widths, standard penetration test procedure gives conservative values of computed settlement as compared to those from Schmertmann's method and vice-versa. It is also observed that the settlement of footings on clays may be highly under-estimated if computed by dividing the compressible clay, stratum into one or two layers only. The actual settlement computed by the division of compressible clay stratum into a number of layer may be as high as two times or even more than that computed treating the compressible stratum as one layer.