Abstract: The borehole shear characteristics of typical Xi'an Q₃ loess were studied using an improved Iowa borehole shear apparatus to guide the application of borehole shear tests in loess areas. The study present the influence of normal stress range, loading shear mode, shear rate, and other factors on test results. The test results showed that when normal stress is controlled within the range of initial stress and critical plastic stress, shear strength and normal stress can be in good agreement with the Mohr-Coulomb failure criterion. When normal stress is less than the initial stress, cohesion is smaller or even negative, and internal friction angle is larger. When normal stress exceeds critical plastic stress, cohesion is larger and internal friction angle is smaller. There is no significant difference in shear strength parameters between single-stage testing and multi-stage testing. When the loess is consolidated at first-stage normal stress for 10 minutes and graded stages for 5 minutes, the normal displacement rate is less than 0.005 mm/min, which can be used as a basis for determining the stability of consolidation deformation. When shear rate is in the range of 1.7-2.3 r/s, the difference between test results of shear strength index is small. The test results of factors affecting shear characteristics of boreholes can be used as a reference for test manipulation and data processing.

Key words: loess, borehole shear test, shear characteristics, shear strength parameters, normal stress