不同初始孔隙比下非饱和黏土渗透性试验研究及模型预测

Experimental study and model prediction of permeability coefficient of unsaturated clay with different initial void ratios

不同初始孔隙比下非饱和土渗透系数的试验测量及预测,是进行非饱和土渗流分析及水-力耦合研究的基础,相关工作具有重要的意义。以湖南邵阳红黏土为例,利用千斤顶制备5种不同初始孔隙密度塑土样;采用压力板仪测量其土-水特征曲线;选用变水头法测量其饱和渗透系数;自制有机玻璃桶试验装置,采用瞬态剖面法进行非饱和渗透试验,测量不同初始孔隙比土样的非饱和渗透系数。选用CCG(Childs和Collis-George)修正模型和陶-孔模型预测非饱和渗透系数,并与实测值进行比较,验证模型有效性。以上述试验及模型预测的成果为基础,研究初始孔隙比对非饱和(相对)渗透系数的影响规律。研究结果表明:湖南非饱和黏性土渗透系数随基质吸力增加而降低,在低基质吸力阶段(100 k Pa以内)变化较为剧烈,在高基质吸力阶段(100 kPa以上)变化较为缓慢;CCG模型预测误差较大,陶-孔模型预测值与实测值总体吻合较好;进气值之后,初始孔隙比对非饱和渗透系数的影响较小,对非饱和相对渗透系数的影响较大,相同基质吸力条件下初始孔隙比越小,相对渗透系数越大。

The measurement and prediction of permeability coefficient of unsaturated soils with different initial void ratios are the basis of seepage analysis and hydro-mechanical coupling study of unsaturated soils, so corresponding work has great significance. As an example, Hunan red clay was chosen to prepare remoulded samples of five different initial void ratios by using jack. Then, the soil-water characteristic curve was measured by using pressure plate apparatus. Afterward, the saturated permeability coefficient was measured by variable head method, while the unsaturated permeability coefficients with different initial void ratios were obtained by instantaneous profile method using a self-made plexiglass barrel device. CCG(Childs and Collis-George) correction model and Tao-Kong model were selected to predict the unsaturated permeability coefficients, and their effectiveness was demonstrated through comparing the prediction values with the measured values. On the basis of experimental results and model prediction values, the influence of initial void ratio on unsaturated(relative) permeability coefficient was examined. The results show that the permeability coefficient of unsaturated Hunan clay decreases with the increase of matric suction in a double logarithmic coordinate, which presents a larger slope in low matric suction stage within 100 kPa while a smaller slope in high suction stage above 100 kPa. The predictions of Tao-Kong model are in good agreement with the measured values, yet great predicted errors exist in the results by the CCG model.For the suction stage larger than air entry value, the initial void ratio has little influence on the unsaturated permeability coefficient and has a greater influence on the unsaturated relative permeability coefficient. In the condition of same matric suction, a smaller initial void ratio results a greater relative permeability coefficient.