In practice, the soil is subject to more than one shear stress in many cases. For instance, the soil in an embankment is subject to a static shear stress along sloping direction, and the sloping direction is usually different from the direction of an earthquake loading. Therefore, there is a necessity to investigate undrained soil behaviors under shear stresses along multiple directions. This paper employs the first commercially available bidirectional direct simple shear apparatus (VDDCSS) to investigate the soil responses of Leighton Buzzard sand under two directional shear stresses. Sand samples are first subject to a static shear stress under drained conditions along different directions from 0~0 to 180~0, followed by a monotonic or cyclic shear stress along 0~0 until failure occurs. In static tests, the soil strength is the lowest when the angle between these two shear stresses is near 90~0, and the strength is the highest at 0°. In addition, a smaller angle leads to a more brittle response, and a greater angle leads to a more ductile response. In dynamic tests, liquefaction resistance is decreased from the angle of 0~0 to 90~0, and then increased from 90~ to 180~0.
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