Wave-induced liguefaction and Flow Deformation in Sand Beds

本报告首先描述了对具有水平表面的砂粒进行的一系列离心波槽试验的结果。不同土层深度超孔隙压力的实测痕迹清楚地表明，在强波条件下，液化首先发生在土层浅层，然后向下扩展，最终使整个土层进入液化状态。利用高速CCD相机捕捉了波浪加载过程中土液界面的运动。结果表明，液化发生后，土液界面在浅土层深度处开始明显振动，且随着时间的推移，土液界面振动振幅随液化锋向下推进而明显增大，当整个土床处于完全液化状态时，振动振幅趋于恒定。这些有趣的观察导致了一个简单但可行的理论模型的发展。它是Lamb（1932）双流体层理论的延伸，在这个意义上，液化土壤被视为具有特定质量密度的无粘性流体，并被亚液化的弹塑性土壤沉积物所覆盖。理论模型的性能与在离心波实验中观察到的结果比较好。此外，通过一系列离心波槽试验，研究了更粗的颗粒状斜坡趾部及其周围的土壤不稳定性。实验结果表明，在自由场的浅土层发生液化后，碎石丘的趾部开始以可识别的速度沉降。这实际上是在波浪荷载过程中液化带的广泛扩散，从而导致整个碎石丘体向液化基砂深处沉降。

This report first describes results from a range of centrifuge wave tank tests performed on sand deposits with a level surface. The measured traces of excess pore pressures at different soil depths clearly indicated that under severe wave conditions, liquefaction first took place at shallow soil depth and then propagated downwards, eventually bringing the entire soil bed into liquefaction. The motion of the fluid/soil interface during wave loading was captured by means of a high-speed CCD camera. The images taken showed that the fluid/soil interface began vibrating significantly upon the occurrence of liquefaction at shallow soil depth, and that the amplitude of soil vibration increased markedly with time in accordance with the downward advancement of the liquefaction front and leveled off at a constant value when the entire soil bed was in a state of complete liquefaction.These interesting observations led to the development of a simple yet workable theoretical model. It is an extension of Lamb's (1932) two-fluid-layer theory in the sense that the liquefied soil is regarded as an inviscid fluid with a particular mass density and is underlain by a deposit of sub-liquefied, elastoplastic soil. The performance of the theoretical model compares favourably with what has been observed in the centrifuge wave experiments.Furthemore, efforts were directed to investigating the soil instability at and around the toe of much coarser granular slopes, through a series of centrifuge wave tank tests. The results from the experiments showed that upon the occurrence of liquefaction at shallow soil depth in the free field, the toe of the rubble mound started settling at an only discernible rate. This was in fact followed by extensive spread of the liquefied zone in the course of wave loading, thereby causing the entire body of the rubble mound to settle deep into the liquefied foundation sand.