By N A Kalteziotis, Athens Public Works Research Centre, B K Menzies, GDS Instruments and A I Tarzi, University of Surrey
This paper was first published in GE’s July 1984 issue.
For a footing on a real soil, shear strains are induced in the soil and vary throughout the zone of influence of the footing. For a saturated clay, the soil behaves in the short term like an incompressible elastic solid and the distribution of shear strain may be obtained. Furthermore, the stress-strain behaviour of a sensitive clay is brittle and may be described as approximating to an elastic-plastic/strain-softening idealisation.
It follows that near collapse the variation in shear strain beneath the footing will mobilise both pre-peak and post-peak shear stresses. Zones at post-peak will have diminished in shear strength and shed load to pre-peak zones. Limiting equilibrium will occur when the load shed by post-peak zones can only just be carried by the pre-peak zones (Bishop, 1971; Menzies and Simons, 1978). A further increment in load will induce progressive failure of the soil.