Soil sample torsion direct shear test device and test method

The invention discloses a soil sample torsion direct shear test device and a test method. The soil sample torsion direct shear test device comprises a load bearing rack, an annular upper box, a lower box, a piston, a loading device, a force measuring system and a vertical pressure pressurizing system, wherein the bottom part of the lower box is fixed on the load bearing rack through a rotary shaft, so that the lower box only has a rotational degree of freedom in a horizontal direction; the annular upper box is arranged above the lower box; the loading device is used for driving the lower box to rotate circumferentially; the piston with the diameter being slightly smaller than the inner diameter of the upper box is placed on the upper part of the upper box; the vertical pressure pressurizing system is used for applying downward pressure on the piston; the force measuring system is used for measuring the torsion of the upper box. The soil sample torsion direct shear test device provided by the invention can ove