半干旱地区天然黄土包气带中氚的运移特征

Transport Characteristics of Tritium in Unsaturated Loess of Semi-arid Area Under Natural Condition

通过氚在黄土包气带现场示踪试验结果的分析 ,发现3H纵向分布在相对浓度较大时是对称的 ,而相对浓度较小时则不对称。通过对横向迁移数据的处理 ,得到了3H在天然黄土中的横向浓度分布方差σ2 y 分别为 6 8 4cm2 (A坑 ,t=780d ,埋深 76cm处 )和 138 5cm2 (B坑 ,t=779d ,埋深110cm处 )。横向扩散参数约为纵向扩散参数的 1/ 3。在埋深较大的B坑中 ,快成分份额 f(t,Uq)随时间变化不大 ,相对速度Uq(t ,xq)随时间的变化也不大。在此前提下 ,按快成分计算出关心地点的浓度在某些情况下大于常规计算结果。这表明 ,以质心运动速度为代表的常规计算在某些情况下是不保守的。

Through analyses of the field tracer migration test results of tritium in unsaturated loess located in semi arid area, it is found that the longitudinal concentration distributions of 3H are symmetry at higher relative concentration and non symmetry at lower relative concentration. From processing of the migration test data the lateral concentration distribution variances ( σ 2 y ) of 3H are obtained. σ 2 y is 68.4 cm 2 (in pit A, at t =780 d and depth of 76 cm) and 138.5 cm 2(in pit B, at t =779 d and depth of 110 cm), respectively. The lateral diffusion parameter is about one third of the longitudinal diffusion parameter. It is found from analyzing faster component of diffusion of 3H that the changes of both the faster component fractions, f(t,U q) , and the relative velocities, U q, with time in pit B are not significant. Under the prerequisite, the concentrations calculated by faster component at point concerned are larger than that by conventional calculation under some conditions. It shows that it is not conservative to use the velocity of the center of mass as representative to conduct conventional calculation under some conditions.