Experimental Study on Earthquake Resistance of Underwater Granular Structures

提出了一种可视化水下粒子组合动态行为的实验技术——激光辅助层析成像（LAT）。根据所提出的方法，由破碎的玻璃颗粒组成的颗粒结构模型浸入具有相同折射率的液体中，从而变得不可见。然后，一个强激光“片”（LLS）穿过它，照亮一个横截面内所有粒子的轮廓线。用LLS扫描模型可以获得每个离散粒子的形状和运动的三维图像，以及模型的整个场变形。将这种方法用于更小的颗粒尺寸将扩大其应用于分析由更细颗粒组成的结构。然而，在这种情况下，要清楚地看到LLS上的每个粒子并不容易。为了克服这个问题，我们开发了一些技术，我们可以将所使用的玻璃材料的晶粒尺寸减小到1毫米或更小。采用该方法对堤形模型进行了动力破坏试验。将筛选后的颗粒（2mm < grain < 5mm）制成的模型在液体中进行正弦振荡。当基底加速度幅值超过阈值时，模型表面开始滑动。阈值加速度随刺激频率的增加而增加，而阈值速度的变化较小，在0.5 ~ 2.0 kine范围内较为分散。利用离散椭圆元法（Discrete Elliptic Element Method， DEEM）讨论了LAT试验中观察到的破坏过程及其频率依赖性，并考虑了整体滑移和滚动对破坏过程的贡献。DEEM模拟让我们大致了解了膨胀效应对整体行为的影响及其频率依赖性。

A new experimental technique to visualize the dynamic behavior of underwater particle assemblage (LAT: Laser-Aided Tomography) was developed. According to the proposed method, a granular structure model, made of particles of crushed glass and immersed in liquid with the same refractive index, consequently becomes invisible. An intense laser-light "sheet" (LLS) is then passed through it, illuminating the contour lines of all the particles within a cross-section. Scanning the model with LLS allows a 3D image of every discrete particle's shape and motion to be obtained as well as the whole-field deformation of the model. Utilization of this method with a smaller particle size will expand its application to analyses of structures made up of finer grains. In this case, however, it is not easy to have a clear look at each particle on the LLS. Some techniques were developed to overcome the problem, and we could reduce the grain size of the employed glass material to lmm or smaller.Dynamic failure test of embankment-shaped models were conducted using the proposed technique. The models made of screened particles ( 2mm < grain < 5mm ) were shaken sinusoidally in the liquid. The surface of the model began to slide when the amplitude of base acceleration exceeded a threshold. The threshold acceleration increased with excitement frequency, while variation of threshold velocity was rather small, and was scattered in the range of 0.5 to 2.0 kine.The failure process and its frequency dependence observed in LAT experiments was then discussed using the Discrete Elliptic Element Method (DEEM), considering contributions of overall slip and roll to the failure process. The DEEM simulation gave us a general idea of the dilatation effect on overall behavior and its frequency dependence.