Effective stress paths and yielding in soft clays below embankments

Current methods of predicting the response of soft clays to surface loading are often unsuccessful because the assumed constitutive relationships, including effective stress path behaviour, are incorrect. In particular, the transition from small-strain to large-strain behaviour (i.e. yielding) is frequently not taken into account. Recent laboratory testing has demonstrated that the behaviour of soft clays is largely controlled by yielding. The locus of effective stress states causing yield is known as the yield envelope (YE).The effective stress paths (ESP's) in soft clay foundations below the centre of six fills were determined from computed total stresses and measured pore-water pressures. Yield behaviour is clearly indicated by ESP shapes. The yield envelopes inferred from analyses of field data are similar to those obtained from laboratory testing. Effective stress path shapes vary widely, depending on a variety of factors, including imposed stress level, rate of construction, and boundary drainage co...