Fundamental study on transition from quasi-static to rapid flow of granular materials

与土有关的结构，如堤防和挡土墙通常是在稳定性分析的基础上设计的。为了分析土体的稳定性，土工需要确定土体的破坏准则，并为此做了大量的研究工作。然而，与土有关的结构破坏每年都在重复发生，流动的土屑对土木工程结构和人类生命造成了巨大的伤害。这一事实表明，不仅是破坏准则，而且破坏后的流动行为对减少这种破坏是非常重要的。土壤运动以沿剪切带的准静态流动开始，如果满足一定条件（尚不清楚），则速度增加，称为快速流动。为了了解从准静态到快速流动的转变行为，进行了室内试验和数值模拟试验，特别关注准静态和快速流动时流动机理的微观方面。结论如下：1)在旋转剪切池中产生了二维的颗粒组合流，并通过高速摄像和图像分析对单个颗粒进行了追踪。研究了颗粒流的微观行为，如颗粒旋转、颗粒温度、碰撞角和速度梯度分布，从微观角度获得了区分准静态和快速流动的判据。2)利用微聚焦x射线计算机断层扫描技术，观察了准静态流场的三维微观结构。在此基础上，提出了基于离散元法（DEM）数值模拟的强支撑剪切带剪胀模型。提出了一种新的微观结构定量表征方法。3)应用DEM数值模拟了从准静态到快速流动的过渡过程，并与室内试验结果进行了比较。研究发现，DEM为模拟颗粒物料从准静态到快速颗粒流动提供了可靠的工具。对DEM进行了扩展，成功地考虑了水对颗粒流动的影响。少

Soil-related structures such as embankments and retaining walls are usually designed on stability analysis. To analyze the stability, soil engineers need a failure criterion of soils, and have done a lot of research works for it. However, failure of soil-related structures is repeated every year, and flowing soil debris causes a huge damage to the civil engineering structures and human lives. This fact implies that not only the failure criterions but also the flowing behavior after failure are very important to reduce such damage. Soil movement starts as quasi-static flow along a shear band, and the speed increases, as called rapid flow, if a certain condition (not understood yet) is satisfied. In order to understand the transition behavior from quasi-static to rapid flow, laboratory tests and numerical simulation tests are carried out, with special interest in the microscopic aspect of flow mechanism during quasi-static and rapid flow. The conclusion are summarized as follows:1)Two-di … More mensional flow of particle assembly is generated in a rotary shear cell, and individual particles are chased by means of high-speed camera and image analysis. Micro-behaviors of granular flow such as particle rotation, granular temperature, collision angle and velocity gradient profile are investigated to obtain a criterion distinguishing between quasi-static and rapid flow from a microscopic point of view.2)Three-dimensional micro-structure in a quasi-static flow domain is observed by means of micro-focus X-ray computed tomography. Based on the results, a new dilatancy model in a shear zone is proposed under strong support from numerical simulation of Distinct Element Method (DEM). A new methodology for quantitative representation of micro-structure is also proposed.3)DEM is applied to simulate numerically transition from quasi-static to rapid flow, and the results are compared with the ones of laboratory tests. It is found that DEM provides a reliable tool to simulate of whole range from quasi-static to rapid granular flow of granular materials. DEM is expanded, with success, so that the effect of water on granular flow can be taken into account. Less