“挡”是当前急务,但要注意基础1998抗洪实践证明“堤”是“防”的关键。从某种意义上说,保卫大堤的胜利就是抗洪斗争的胜利。因此,加固长江大堤是当前急务,无可争议。但是从地学角度看,大堤的坚固不仅在于其本身的钢筋水泥,还在于它的基础:其一,长江中游干堤大都建在具二元结构的第四纪冲积层之上,即下面是含水透水的河床相(砂层),上面是较不透水的河漫滩相(亚粘土和粘土)。人人皆知在砂层上建大厦,水一冲就要跨,因此搞清大堤的基础极其重要。许多江段的河漫滩相已被切穿,江水已与大堤两岸地下水呈连通状态,在堤内堤外水位差的压力作用下,江水必然通过河床相(砂层)透水层向堤内渗透,一旦遇到相对薄弱的地方就会刺穿上覆河漫滩层,形成管涌,这是影响大堤安全的主要隐患。要使这种隐患得以杜绝,应采取加固基础防渗漏的 “Block ” is currently a matter of urgency, but to pay attention to the foundation 1998 flood practice has proved “embankment ” is “anti” "key. In a sense, defending the levee’s victory is the victory of the fight against floods. Therefore, it is undoubtedly urgent to reinforce the Yangtze River embankment. However, from an earth science perspective, the embankment is not only strong in its own reinforced concrete, but also in its foundation: First, most of the main dike in the middle reaches of the Yangtze River is built on a Quaternary alluvial layer of binary structure, that is, Permeable bed facies (sand), above which is the more impermeable floodplain (loam and clay). It is well known that constructing a building on a sandstone floor requires a single cross-over of the water, so it is extremely important to understand the foundation of the dike. River floodplain in many sections has been cut through. The river water has been connected with the groundwater on both banks of the embankment. Under the pressure difference of the water level outside the embankment, the river will inevitably infiltrate into the embankment through the permeable layer of river bed (sand layer) Weak places will pierce the overlying river floodplain, the formation of piping, which is the main risk affecting the safety of the dike. To make this hidden danger can be eliminated, should be taken to strengthen the foundation of anti-seepage