Visualization of Seepage Failure of Sols by X-ray TV System

本研究的目的是利用x射线电视可视化技术来研究无黏性土的渗流破坏过程。一系列的渗流试验进行了均匀的砂沉积，在间隙分级颗粒介质和层状颗粒材料具有明显的对比，在他们的颗粒大小。所得的主要结果可概括如下。在渗流逐渐加剧、向上流动的条件下，均质砂土在符合Terzaghi公式的临界水力梯度处发生沸腾，但x射线图像清楚地表明，沸腾破坏具有进行性，实际上在沸腾破坏发生之前，土体中存在明显的局部变形。在间隙分级的颗粒介质中，观察到管道以这样一种方式发生，即较细的颗粒通过较粗颗粒的空隙被冲走，而在颗粒骨架中只留下微不足道的变形。在砂砾层与砂砾层的两层体系中发生的渗流破坏值得特别注意。破坏以砂土层局部液化带的形式开始。当液化锋延伸至上覆砾石层时，成群的砾石颗粒脱落并依次深入液化砂带。值得注意的是，液化砂的上部通过砾石层的空隙上升。整个系统的最终失效形式是剧烈沸腾，伴随着拉威尔层的完全坍塌。

The purpose of this study was to make use of X-ray TV visualization techniques for investigating the process of seepage failure in cohesionless soils. A range of seepage tests were performed on homogeneous deposits of sand, on gap-graded granular media and on layered granular materials having a marked contrast in their grain sizes. The principal results obtained may be summarized as follows.1. Homogeneous deposits of sand under conditions of gradually intensified, upward seepage flow underwent boiling at critical hydraulic gradients conforming to Terzaghi's formula, however X-ray images clearly indicated that the boiling failure was of a progressive nature and was in fact preceded by marked local deformations in the soil mass.2. In gap-graded granular media, piping was observed to occur in such a way that finer particles were washed away through the void spaces of coarser particles, yet leaving only insignificant deformation in the granular skeleton.3. The seepage failure that occurred in a two-layer system with a gravel layer resting on a sand layer, deserves special attention. The failure started in the form of localized liquefaction zones in the sand layer. When a liquefaction front extended to reach the overlying gravel layer, groups of gravel particles came off and successively penetrated deep into the liquefied sand zones. Notably, the upper part of the liquefied sand rose up through the void spaces of the gravel layer. The final form of failure of the entire system was violent boiling, accompanied by complete collapse of the ravel layer.