饱和悬浮塑料砂流动变形可视环剪试验研究

为了分析剪切条件下零有效应力状态砂土的流动变形规律，对传统环剪仪进行了试样可视化改造，研制了透明环形剪切盒，通过对剪切盒膨胀性能分析及与标准砂的剪切试验对比，验证了环剪装置改造的合理性。通过分析不排水条件下饱和悬浮塑料砂的剪应力-应变曲线，发现其剪切强度具有应变软化的特性。通过分析环剪仪中饱和悬浮塑料砂试样的有效应力，证实了可视环剪试验中的土体基本处于零有效应力状态。开展了饱和悬浮塑料砂的流动变形可视环剪试验研究，结果表明：饱和悬浮塑料砂在固结不排水条件下剪切变形不连续，直接在剪切面发生断裂；在不固结不排水的条件下饱和悬浮塑料砂的剪切变形表现出流动形态，且与剪切速率有关：在低剪切速率下，剪切变形仅在剪切面处形成具有曲线轨迹的流动变形而在其他区域不发生变形；而在高剪切速率下剪切变形为整体的倾斜变形，符合黏性流体的流动变形特征。

Study of flow deformation of saturated suspended plastic sand by visualized ring shear tests

In order to analyze the flow deformation of sand under zero effective stress and shearing condition, traditional ring-shear apparatus is modified with the transparent box for specimen visualization. By analyzing the expansion of transparent box and comparing the shear tests of standard sand, the rationality of the ring-shear apparatus after the reformation is validated. By analyzing the shear stress-strain curves of saturated suspension plastic sand under unconsolidated undrained condition, strain softening is found in the shear strength. And by analyzing the effective stress of saturated suspended plastic sand, it is proved that the saturated suspended plastic sand in the visual ring shear tests is in zero effective stress state. The results show that the shear deformation of the saturated suspended plastic sand under the consolidated undrained condition is obviously discontinuous. Fracture occurs directly on the shear plane. The shear deformation of the saturated suspended plastic sand under unconsolidated undrained condition has distinct flow characteristics. The deformation characteristics are related to the shear rate. Under the low shearing rate, the shear flow deformation only forms on the shear plane and shows curved trajectory. But under the high shear rate, the shear flow deformation is totally incline, and consistent with the flow deformation of viscous fluid.