水位降落条件下非稳定渗流试验研究

Unsteady Seepage Test under Condition of Rapid Drawdown

水位降落时产生的非稳定渗流场对坝坡的渗流和稳定影响较大。通过砂槽模型室内试验模拟了粉砂、细砂、黏土等多种材质的边坡在水位降落过程中的非稳定渗流物理过程,分析了水位降落过程中上游边坡的渗流场特点,比较了不同边坡材料、渗透特性、坡比和水位降落速度的泄水过程中边坡渗流场自由面形式和等势线变化特点,重点研究了给水度μ、渗透系数k、库水位降落的速度v对自由面最高点、上游边坡中的孔隙水压力、坡降的影响,定量分析了水位降落时k/μv判断骤降、缓降、快降的标准,探讨了非稳定渗流浸润线的计算公式。结果表明:渗透系数小、给水度大的土坡在水位降落过程中产生的上游边坡孔隙水压力值和渗透坡降较大,非稳定流场自由面最高点位置也更高;水位降落时的上游边坡渗流方向指向坡面;浸润线最高点高度与坡前水深的比值h0/H与降落时间t/T间存在线性关系,k/μv作为判断骤缓降的指标与其线性系数呈指数关系。

The unsteady seepage field caused by reservoir or river water level drawdown is complex and difficult to determine. In this paper, the physical processes of unsteady seepage and slope stability were simulated in the sand- box with silt, fine sand, clay. On the basis of the result of sand-box tests, the characteristics of the seepage field during upstream water level drawdown in front of the slopes was analyzed, the free surfaces and equipotential lines in slope seepage field with different permeability materials, slope forms and drawdown velocities of the outside water level were compared. The influences of storativity μ, permeability coefficient k and decline velocity of reservoir water level v on the maximum high point of free surface, pore water pressure in upstream slope and seepage gradient were researched. The standard to judge the sudden decline, gradual decline and quick decline of reservoir water level using k/μv was quantitatively analysed, and calculating saturation line formula was discussed. The results show that the pore pressure and infiltration gradient inside upstream slope during the water level decline are higher with smaller permeability coefficient and larger storativity inside soil slope, and the position of the maximum high point is also more high, that the seepage direction of upstream slope points to upstream slope surface, and that there exists a linear relationship between the ratio of the height of maximum point of saturation line to water depth ho/H and relative decline time t/T, and an exponential relationship between the unsteady seepage judgement index k/μv and its linear coefficient.