中文摘要：

采用波流水槽试验，针对上覆粗砂层双层砂土进行局部冲刷机理研究，并与中国和美国规范的局部冲刷深度计算方法对比分析．试验研究表明：由于上覆粗砂层的存在，冲刷前期进展缓慢，后期主要为细砂层冲刷，发展较快；而上覆粗砂层对下卧细砂层冲刷起到抑制作用，粗砂层越厚，抑制效果越明显；中美规范对于上粗下细双层砂土局部冲刷深度计算结果偏大，应进行适当折减，以更为合理地反映粗砂层对细砂层冲刷的影响．

英文摘要：

In this paper, flume model test on local scour around piles embedded in composite sand was performed, and comparisons and discussions of such predictions of local scour depth in current China and America were also made. The test results show that the scoring progress is slow because the main scoured parts are coarse sand in the early stage. However, in the later stage, as the fine sand becomes the main scoured parts, the progress is faster. The upper-layer coarse sand can help to keep the lower-layer fine sand from being scoured, and the thicker the coarse sand layer was slower than the fine sand will be scoured. The present design codes of China and USA both work well, but these codes often lead to a much exaggerated results. Therefore, to reflect the effects of the coarse sand on the fine sand, the scour depth should be reduced.