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研究无粘性土中的渗流破坏过程。一系列渗流试验是在均匀的沙堆上，在间隙级配的颗粒介质上，以及在它们的颗粒尺寸有显著差异的层状颗粒材料上进行的。所获得的主要结果可概括如下：1.在逐渐加强的向上渗流条件下，均匀的沙堆在符合太沙基公式的临界水力梯度处沸腾，但X射线图像清楚地表明，沸腾破坏是渐进的，实际上在土体发生明显的局部变形之前。在间隙分级的颗粒介质中，观察到管道发生的方式是，较细的颗粒通过较粗颗粒的空隙被冲走，但在颗粒骨架中只留下不明显的变形。砂层上有砾石层的双层系统中发生的渗流破坏问题值得特别关注。破坏以砂层中局部液化区的形式开始。当液化锋延伸到上覆砾石层时，成群的砾石颗粒脱落并相继深入液化砂层。值得注意的是，液化沙子的上部从砾石层的空隙中冒了出来。整个系统的最终失效形式是剧烈沸腾，并伴随着RAVEL层的完全崩溃。

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.