粉砂岩卸荷破坏全过程的试验研究

对粉砂岩试样进行了常规三轴加载后保持轴向变形不变的峰前、峰后卸围压试验，得到了峰前、峰后卸围压全过程曲线。在此过程中，试验机不再对岩样压缩做功，岩样的破坏是通过自身储存的变形能来实现的。对岩样破坏特征、强度和变形特性的分析结果表明：对于峰前卸围压，岩样表现出脆性剪切破坏的特征，而对于峰后卸围压，则表现出张剪破坏的特征，峰前卸围压破坏比峰后卸围压破坏更具有突发性；对于峰前、峰后卸围压，岩样都表现出明显的侧向扩容现象；岩样破坏时的轴向承载能力对围压都很敏感，这实际上是破裂块体之间的镶嵌组合，反映了试件沿破裂面摩擦滑动的结构效应。

EXPERIMENTAL STUDY ON THE TOTAL FAILURE COURSE OF SILTSAND UNDER UNLOADING CONDITION

Unloading confining pressure tests are conducted at the pre-peak and post-peak of siltsand 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.