堤基非稳定水压力传递滞后效应研究

洪水灾害过程中,堤防上游水头快速变化,作用在堤基土体上的水压力是非稳定的。选取常见的堤基砂土作为试验材料,利用自行设计的试验装置,研究洪水灾害时非稳定水头条件下,堤基无黏性土渗径长度、孔隙比、渗透系数以及颗粒粒径等因素对水压力传递滞后效应的影响规律。研究结果表明:土体颗粒粒径越大水压力传递滞后效应越弱,直径>2 mm的细砾土中水压力传递滞后效应基本可以忽略;上游水头水力梯度提升的越快,下游水压力启动和稳定滞后时间越短,但下游水压力恢复滞后时间越长;水压力传递滞后时间与土体孔隙比呈反比关系;下游水压力启动和稳定滞后时间与渗透系数呈对数关系。

Study on Water Head Lag Effect of Unsteady Seepage in Dike Foundation

During flood disaster, the water head at the upstream of the embankment changes rapidly, and the water pressure acting on the embankment soil is not stable. In order to study the water head lag effect in cohesionless soil under unsteady seepage conditions, water permeability test was conducted through a self-designed test device. Three kinds of test materials including fine pebble, fine sand and middle sand were chosen. The impact of seepage path length, void ratio, permeability coefficient and particle size of cohsionless soils on water head lag effect under unsteady seepage conditions was studied, considering the factors of start-up of seepage, stability of downstream water pressure and recovery of hysteresis. The results show that: the larger the particle size is, the weaker the water head lag effect is. The water head lag effect can be ignored in the fine pebbles with grain size larger than 2 mm; the faster the hydraulic gradient of the upstream head rises, the shorter the downstream water pressure start-up and stabilization lag time is. But the downstream hydraulic pressure needs a longer time to recover; the relationships between the void ratio and permeability coefficient of the cohesive-free soil and the downstream water pressure transmission delay time are both inversely proportional;the permeability coefficient is in a logarithmic relationship with the start-up and stabilization lag time of the downstream water pressure. The results of the study reveal the law of water head lag effect in the cohesive-free soil, which is of great significance in studying the most dangerous moments of flood peaks during flood season and arranging flood protection and emergency rescue.