Plane strain tests on strain softening soils

Some aspects are discussed of the plane strain testing of geomaterials. The plane strain apparatus is particularly suited for investigating the shear band formation in prismatic samples and for evaluating the soil behaviour under different principal stresses, even though only two of them can be independently imposed. After recalling the basic features of the apparatus some preliminary results are presented concerning the behaviour of medium dense sand and of overconsolidated kaolin. The experimental results permit, in particular, to evaluate the accuracy with which the plane strain condition is attained during the test.