多孔介质中两相流动过程的毛细滞回效应

EFFECT OF CAPILLARY HYSTERESIS ON TWO-PHASE FLOW IN POROUS MEDIA

含水量大小以及干湿循环变化历史对多孔介质渗流过程有着重要影响。基于多孔介质理论和毛细滞回内变量模型,建立能够考虑含水量变化历史影响的多孔介质两相流动模型,并利用开发的U-DYSAC2有限元程序进行相应的数值模拟。通过模拟结果与试验数据的比较,验证所建数值模型在模拟复杂条件下非饱和多孔介质渗流问题的可靠性与有效性。对干湿循环变化条件下土质边坡渗流过程进行数值分析,结果表明:毛细滞回效应对非饱和土渗流过程具有显著影响,非饱和土水力状态不仅取决于当前含水量或基质吸力大小,而且还与土体所经历的水力历史有关;特别地,如果利用主脱湿线来描述土水特征关系,那么土体中基质吸力的预测结果会偏高,从而使得传统边坡稳定性分析方法高估土体抗剪强度以及坡体安全系数。因此,在模拟非饱和多孔介质复杂渗流问题时必须要考虑毛细滞回效应。

The seepage process in porous media is significantly influenced by water content and drying/wetting history that the material has experienced.Based on the continuum theory of porous media and an internal state variable-based model of capillary hysteresis,a two-phase flow model of porous media is created and implemented into the U-DYSAC2 finite element code.Comparing with the experimental data,the results show that the proposed model can be reliably and efficiently used to simulate the unsaturated seepage problems of porous media under complex conditions.The new procedure is used to analyze the seepage processes in a soil slope subjected to drying/wetting cycles.The results show that the effect of capillary hysteresis on unsaturated seepage process is significant;and the hydraulic state of soil is not only related to the current value of water content or matric suction,but also depends on the drying/wetting history that the soil has experienced.In particular,it is shown that if the main drying soil-water characteristic curve is adopted in the analysis,the matric suction of soil will be over-predicted;hence the shear strength of soil and the factor of safety of slope stability can be over-estimated based on the traditional methods of stability analysis.Therefore,it is necessary to take into account the effect of capillary hysteresis in modelling unsaturated seepage problems.