Plasticity theory without yield surfaces

EXPERIMENTAL AND THEORETICAL WORK, DESIGNED TO EXPLORE THE POSSIBILITY OF A SOIL PLASTICITY THEORY NOT BASED ON INCREMENTAL THEORY, IS DESCRIBED. THE RESULTS SUGGEST SOME SIMPLE MODELS OF STRESS-STRAIN BEHAVIOUR WHICH COULD FORM THE BASIS FOR FURTHER STUDY. IT IS SHOWN THAT PLASTICITY THEORIES WHICH AVOID THE USE OF THE YIELD SURFACE CONCEPT ELIMINATE SOME DIFFICULTIES BUT INTRODUCE NEW ONES AND IT IS QUESTIONABLE WHETHER THEY MAKE POSSIBLE A MORE ECONOMICAL FORMULATION OF SOIL PLASTICITY THEORY.