包气带岩性结构对降雨入渗能力的影响

降水是鄂尔多斯盆地风沙滩地区地下水的主要补给来源之一,区内包气带岩性结构影响着降雨入渗补给地下水的过程。试验以该区两组均质结构(风积沙、风化砂岩)与两组层状"上粗下细"结构(风积沙-风化砂岩组、风积沙-淤泥质沙组)中水势和水量变化情况分析不同岩性中降雨入渗过程的差异性。结果表明:均质结构和层状"上粗下细"结构降雨入渗过程均呈线性变化过程,但是均质结构的累计入渗量为层状结构的1.5～3.0倍,更有利于降雨入渗;层状"上粗下细"结构中,岩性由粗到细水力梯度增大1.48～1.78倍,下覆细质土较大的水势梯度反映了其低渗性,且降水入渗过程与上覆粗质土无关,主要由下层细质土控制,下层细质土颗粒越细,入渗量越小,较细细质土的入渗量约为较粗细质土的0.66倍。研究结果对于提高鄂尔多斯盆地风沙滩地区水资源评价的准确性具有重要意义。

Influence of lithologic structure of vadose zone on rainfall infiltration capacity

Ｒainfall is the main source of groundwater recharge in aeolian sand area of Ordos basin，and the lithologic structure of the vadose zone affects the process of groundwater recharge by rainfall infiltration. The lithologic structure of typical vadose zone in this area，according to the changes of hydraulic head and water quantity，the difference of rainfall infiltration process between the homogeneous structure in this area，and the difference of rainfall infiltration process between the homogeneous structure( aeolian sand andweathered sandstone) in this area and the layered“upper coarse and lower fine”structure( aeolian sand-weathered sandstone and aeolian sand-silty sand) are analyzed. The result shows that the rainfall infiltration process of homogeneous structure and layered structure is linear，but the cumulative infiltration amount of homogeneous structure is 1. 5 ～ 3. 0 times that of layered structure，which is more conducive to rainfall infiltration. In the layered“upper coarse and lower fine”structure，the larger water potential gradient of the underlying fine soil reflects its low permeability，and the hydraulic gradient of lithology from coarse to fine increases by 1. 48 to 1. 78 times，and the infiltration process of precipitation is not related to the overlying coarse soil，and is mainly controlled by the lower fine soil. The finer the particles in the lower fine soil，the smaller the infiltration amount. In fine soil，the infiltration of fine-grained soil is about 0. 66 times that of coarse-grained soil. The results are of great significance to improve the accuracy of water resources evaluation in aeolian sand area of Ordos basin.