VOLUMETRIC LOCKING ANALYSIS AND ELEMENT CHOICE IN 3D ELASTOPLASTIC ANALYSIS OF SOIL

Traditional low-order elements may suffer the problem of volumetric locking in the analysis of soil under the condition of volume-preserving or dilatant/contractant plastic flow. Taking a Mohr-Coulomb type of soil as example, the relationship between plastic shear strain and plastic volumetric strain is deduced, and the reason behind volumetric locking is revealed. Several types of elements are examined. It is shown that the eight-noded brick element is of serious volumetric locking and Wilson's incompatible element has also the same problem, while the enhanced assumed strain (EAS) element and the fourteen-noded block element adopting reduced integration can overcome volumetric locking. Numerical examples of element tests and bearing capacity calculation of a square footing confirm the claim. Suggestions are given for choosing effective and reliable elements.