黄土包气带水分运移的现场研究

A FIELD STUDY ON MOISTURE MIGRATION IN LOESS AERATED ZONE

本文主要介绍在核素迁移试验现场进行的黄土包气带水分运移研究的方法和主要结果。包气带水分运移试验场建有一座 9.0 m深的负压计观测竖井和二个 2 8.0 m深的中子仪测管。分别采用 WM- 1型负压计系统和 IHiii型土壤中子水分仪测量黄土剖面的基质势和含水量。一组负压计和中子仪测管在天然条件下测量 ,连续观测 2年多 ,用于水分运移特征研究 ;另一组测量停止淹灌后的水分再分配过程 ,连续观测 7个月 ,用于非饱和渗透系数测定。结果表明 :(1)降雨入渗主要影响深度、蒸发影响深度在 1.0 m以上 ;(2 )水分运移可分为 4个带 :1.0 m深度以上为强交替带 ,含水量、水势和水势梯度随时间变化快、变幅大 ,液态水的运移比较明显 ;1.0～ 7.2 m深度上为含水量和水势随时间变化小的弱交替带 ,除黄土颗粒大小变化较大的深度处 ,一般来说 ,水势梯度方向单向向下 ,其中 :含水量和水势在 1.0～ 1.6 m深度上随时间变化较大 ,液态水的运移也比较明显 ;在 5.0～ 7.2 m深度上 ,水分变化很小 ,基本趋于稳定状态 ,液态水的运移很不明显 ,微弱的热水汽扩散显现出来 ;在 7.2～ 2 3.0 m深度上 ,含水量除在黄土 -古土壤 -钙质结核层组合交界处有变化外 ,其余则基本保持与黄土颗粒大小变化相对应的稳定状态 ,为水分运移的传递带 ;2 3.

In this paper, the methods and main results of a study on moisture migration in aerated zone at CIRP's Field Test Site are presented.The facility for the study consists of a tensiometer shaft down to a depth of 9.0 m and 2 neutron probe access tubes down to a depth of 28.0 m. A set of theirs was used to monitor the moisture migration under natural condition for 2 years, and another set was used to determine unsaturated hydraulic conductivity under the after ponding and water redistribution for 7 months. Soil matric head and water content profiles were monitored by a tensiometer system (model WM 1) and a neutron soil moisture probe (model IH iii ). The results indicate: (1) the depth essentially effected by rainfall and the depth effected by evaporation are in the upper 1.0 m; (2) the moisture migration may be divided into four zones: the layer in the upper 1.0 m of the soil is a strong exchange zone, in which the magnitude of water content and the direction and magnitude of hydraulic head gradient vary incessantly, and the migration of liquid water is obvious;the layer in depth from 1.0 to 7.2 m is a weak exchange zone where the direction of hydraulic head gradient is downward except for the depths of more changes in grain size, in which in the depth from 1.0 to 1.6 m the changes in the water content and hydraulic head are comparatively large, and in the depth of 5.0 to 7.2 m their variations are very small, the moisture migration basically appears in a stable state and a weak thermal vapor diffusion was appeared; the layer, ranging from 7.2 to 23.0 m in depth, is a retentive zone, in which changes in soil water content with depth correspond to the variations in loess grain size except for the interface of loess paleosoil beds; and the layer in the depth of 23.0 to 28.0 m is capillary water zone; (3) at the depth of 0.4 to 2.4 m the conductivity ranges from 3.6×10 -3 to 23.4 cm/d when volumetric water contents are 0.18 to 0.41, fitting relation of unsaturated hydraulic conductivity versus water contents,this relation can be applied to the Malan Loess's upper segment for these water contents; (4) in the layer for the stable moisture migration the cumulative annual recharge calculated by an annual average means and Darcy Equation is less than 1 cm; (5) in mid dry loess zone thermal vapor diffusion may be another way of groundwater recharge. (