Constitutive laws and numerical analysis for soil foundations under static, transient or cyclic loads: Fid-Bau Portal

Constitutive laws and numerical analysis for soil foundations under static, transient or cyclic loads

Zienkiewicz, O.C.

Abstract In this paper we present the survey of research carried out over the past ten years at University College of Swansea under the guidance of the author to determine a rational approach to the study of foundation and other soil mechanics problems. The paper starts with a description of the need for numerical approaches utilizing finite element or similar methodology and discusses various constitutive models for static soil behaviour. Plasticity is adopted to describe the non-linear characteristics of soil. A series of tests on ideally elasto/plastic, associative and non-associative, models and on an extended critical state model show that with the latter it is possible to obtain good predictions of the behaviour for drained and undrained behaviour of normally consolidated materials and indeed to extend the results to over-consolidated situations. The remainder of the paper concerns itself with the cyclic and transient load behaviour. Here the well known increase of pore pressure under repeated loading has to be accounted for as this can either lead to liquefaction or a very considerable weakening of the material. Two alternative approaches are proposed. In the first a concept of an autogenous densification of the material is introduced to supplement the original elasto/plastic models and this is shown to be effective in predicting liquefaction of sands. An alternative model modifies the critical state using methods proposed by Mroz to describe behaviour of clays more accurately. Finally, the paper deals with shakedown or ratchetting type problems in which it is possible to obtain collapse without material deterioration merely by a sufficient number of cyclic load repetitions. The numerical methods of dealing with such problems are discussed.