Abstract:In order to explain the failure and breakage mechanisms of structural geological materials,the plane strain compression tests of the samples of bar-like structural bodies assembled in two patterns are conducted under unloading situations. In the process of reducing the lateral stress,it is found experimentally that the structural bodies not only slide and rotate,but also can be broken and the main failure modes of structural bodies are shear failure and splitting;while the samples assembling of bar-like structural bodies are broken gradually,the strain hardening or strain softening can be observed and breakage bands are macroscopically formed in the end;the volumetric strain of the samples is always contractive but the lateral strain turns to be the laterally extensive gradually.