Determination of the direction of plastic strain increment for geomaterials

As shown in a great amount of test results and theoretical analyses, the direction of plastic strain increment for geomaterials is different from that of stress. The direction of plastic strain increment for metals is determined by the stress on its characteristic plane-octahedral plane and it is the same as the direction of stress. Based on the analogy between geomaterials and metals as well as the concept of the characteristic plane, the direction of plastic strain increment for geomaterials can be determined by the direction of the stress on their characteristic plane (SMP plane). The equations for the determination of the direction of plastic strain increment are proposed. They can be applied to the cohesive materials by adding a material parameter. Finally these equations are validated by the test data. The proposed equations are also used in Modified Cam Clay revised by transformed stress, which can simulate the test data well.