Stress state and noncoaxiality of Leighton Buzzard sand in NGI-type bi-directional simple shear tests

In NGI-type simple shear apparatus, including recently developed NGI-type bi-directional simple shear apparatus, the complete stress state is unknown which limited the interpretation of test results. This study compares the stress state of NGI-type simple shear test obtained by two methods, the stress state determined by an empirical method using test data, and stress state determined by measured values in a corresponding DEM test. Results showed that (1) stress state obtained by the two methods shows good agreement, especially at simple initial stress conditions. (2) due to the underestimation of constant k, minor principle stress and horizontal stress interpreted by the empirical method are higher than that in DEM test, and noncoaxiality interpreted by the empirical method are lower than that in DEM test. It is recommended that before determining the stress state of NGI-type bi-directional drained simple shear tests, it is needed to perform a test and corresponding DEM test under simple stress condition. The empirical equations for horizontal stress, especially the constant k should be validated and corrected for the tested soil before interpreting the stress state.

Automated summary

The study found that the stress state obtained by the two methods shows good agreement, especially under simple initial stress conditions. However, due to the underestimation of the constant k, the minor principle stress and horizontal stress interpreted by the empirical method are higher than that in DEM test, while the noncoaxiality interpreted by the empirical method is lower than that in the DEM test.