Loose sand is highly susceptible to liquefaction

and small changes in stress state can affect its liquefaction characteristics. Based on multi-directional cyclic simple shear tests

this study conducted cyclic simple shear tests on loose sand under different magnitudes and directions of static shear stress

and complex shear paths. The cyclic simple shear characteristics of loose sand under complex initial stress states are studied. The main conclusions are drawn as follows: (1) As the static shear stress ratio increases

the peak shear stress of the specimen increases

the increment of pore water pressure in the first cycle increases

and the specimen is more prone to liquefaction. The effect of the magnitude of initial static shear stress on excess pore water pressure is more significant at the early stage of shearing. (2) With the increase of the angle between the initial static shear stress and the main direction of dynamic shear stress

the peak shear stress of the specimen in the X direction decreases

and the pore water pressure of the specimen accelerates to increase. In addition

the increment in pore water pressure in the first cycle and the last cycle increases

and the difference between the cycles increases. The specimen is more prone to sudden liquefaction. (3) The specimen with 8-shaped shear path has the largest area of stress−strain hysteresis loops

which consumes the most energy per cycle

followed by the specimen with the circular shear path

and the specimen with the straight shear path has the smallest area. Complex shear paths can induce a sudden increase in pore water pressure at the beginning of shearing

increasing the increment in pore water pressure in each cycle and making it more prone to liquefaction. (4) The sequence of factors affecting the liquefaction of loose sand is the angle between the initial static shear stress and the dynamic shear stress

the shear path

and the magnitude of the initial static shear stress.