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

本研究旨在利用X光电视显示技术，探讨无黏性土之渗透破坏过程。对均匀砂质沉积物、间隙级配颗粒介质和粒度对比明显的层状颗粒材料进行了一系列渗流试验。主要结果如下：1.均匀沉积的砂在逐渐加强的条件下，向上的渗流在符合太沙基公式的临界水力梯度下发生沸腾，然而X射线图像清楚地表明沸腾破坏是渐进的性质，实际上在土体发生明显的局部变形之前.在间隙分级颗粒介质中，观察到管道的发生方式是，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微不足道的变形。3.在砂层上覆砾石层的双层系统中发生的渗透破坏值得特别注意。破坏开始于砂层中局部液化区的形式。当液化前缘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，伴随着松散层的完全崩溃。

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.