非饱和土粒间毛细作用的微观不连续变形分析

MICROSCOPIC DISCONTINUITY DEFORMATION ANALYSIS OF CAPILLARY IN UNSATURATED SOIL

非饱和土粒间毛细水作用是其基质吸力的主要来源。本文基于二维非连续变形分析算法(DDA),建立了一种能够模拟不同饱和度下毛细水分布状态及计算土水特征曲线的扩展DDA算法。该算法首先通过反复迭代的方式来计算出不同饱和度下毛细水弯液面的半径,并利用圆心轨迹交汇法确定粒间毛细水弯液面与颗粒的搭接位置,从而确定各个颗粒表面被毛细水浸湿的区域。而后利用Young-Laplace方程计算出各个浸湿区域毛细负压的大小,并将其与表面张力添加到传统DDA算法控制方程中。为验证该算法,参照真实黄土中含量最多的粗颗粒建立一理想黄土微观土骨架模型,模拟了不同饱和度下土体中的毛细水分布状态,并获得了土水特征曲线。将模拟结果与实测的土水特征曲线进行对比分析,结果显示预测值和实测值基本一致,该方法能够从微观上揭示非饱和土粒间吸力作用的本质。

Capillary action is one of significant sources of matric suction in the unsaturated soil.So we propose a new method based on two-dimensional Discontinuous Deformation Analysis(DDA)to simulate the distribution of capillary water and to calculate soil water characteristic curve(SWCC)under different saturation.Firstly,the radius of capillary water meniscus is calculated with iterative algorithm method,and circle center trajectory intersection method is used to determine capillary water distribution in this algorithm.Then,the matric suction,calculated with Young-Laplace equation,is taken into account in the control equation of the original DDA method with the surface tension.Moreover,in order to verify the accuracy of the algorithm,an ideal loess structure model is established.In this model,the soil particles used are mainly coarse particles with high content of loess.The particle size distribution and shape accord with the actual values.And then,the model is used to simulate the distribution of capillary water and to calculate soil water characteristic curve(SWCC).The results show that simulated SWCC contains boundary effect stage,transition stage and residual stage.The distribution of capillary water is simulated at each stage.In addition,the result comparison between the numerical simulation and the experimental data shows the simulation results agree well with experimental data,which suggest that this method is available for simulating capillary action in unsaturated soil.