Noncoaxial Behavior of a Highly Angular Granular Material Subjected to Stress Variations in Simple Vertical Excavation

Abstract

Experiments were carried out using a dynamic hollow-cylinder apparatus (HCA) to investigate the effects of stress paths and principal stress rotations experienced during a simple vertical excavation on the element-scale deformation and noncoaxial behavior of a highly angular granular material. For this purpose, an improved specimen preparation technique was used to generate homogeneous HCA specimens using a multilayer undercompaction method. The stress paths used in the HCA experiments were extracted from the numerical results obtained in a discrete element simulation of a simple vertical excavation, where complex stress paths and principal stress rotations have been observed. The experimental results show that different stress paths and rotations in excavation significantly affect the element-scale deformation behavior. Noncoaxial behavior (i.e., the deviation of plastic strain increment direction from the principal stress direction) was observed in the HCA tests, which was a result of the combined effects of stress history, mean stress, deviator stress, and principal stress rotation. The deviator stress seems to have a more apparent effect than the mean stress on noncoaxial behavior. The experimental data will be useful in understanding the basic behavior of lunar soil under excavations because both materials share the similar macroscopic and microscopic characteristics.