Non-linear soil stiffness in routine design

Soil stress-strain behaviour is highly non-linear and this has an important influence on the selection of design parameters for simple routine geotech nical calculations. Non-linear behaviour can be characterized by rigidity a nd degree of nonlinearity and these can be determined from measurements of very small strain-stiffness, peak strength and failure strain. Very small s train-stiffness can be found from measurements of shear wave velocity in si tu or in laboratory tests. Peak strength and failure strain can be measured in routine laboratory tests but are strongly influeuced by initiation of s hear bands. The important non-linear stiffness parameters for soil are rela ted to its composition and to its current state. Back-analyses of the load settlement behaviour of full-scale and model foundations demonstrate the in fluence of non-linear soil behaviour. Variations of stiffness,vith settleme nt calculated from full-scale and model foundations agree well with non-lin ear soil stiffnesses based on rigidity and degree of non-linearity. These r esults suggest a simple method for routine design which takes account of so il non-linear stiffness.