Abstract：Unloading confining pressure tests are conducted at the pre-peak and post-peak of siltsand specimens with fixed displacement after conventional triaxial compression. In this course，testing machine does not do any works for specimens. The failures are caused by deformation energy of themselves. Based on the complete procedure of unloading confining pressure，the failure features，deformation and strength of siltsand specimens are analyzed. The test results show that unloading fracture mode is shear failure at the pre-peak and tensile-shear failure at the post-peak. Failure is easier to happen suddenly in the process of unloading confining pressure at the pre-peak than that at the post-peak. All specimens show strong dilatancy. In addition，the axial supporting capacity is very sensitive to the change of confining pressure. This is the result of the mosaic community between fractured rock blocks and reflects the structure effect along friction-sliding surface.
