近年来超深黄土填方工程成为西北黄土沟壑区扩展城市空间的有效手段，然而超深黄土沟壑填方工后内部水分场再平衡过程对其渗透和工后沉降发展产生至关重要的影响。目前关于填方渗透特性的研究主要集中在地表水分入渗和局部毛细水上升等迁移路径，很少考虑土体应力状态对渗透特性的影响。对于填方厚度较大的超深黄土填方工程，应力作用对其渗透特性的影响是研究地下水分场再平衡过程必须考虑的关键因素。

本文以延安新区填方黄土为研究对象，通过现场调研、室内试验、理论分析与数值模拟等方法，研究了填方黄土在水力耦合作用下的固结湿陷变形规律和渗透特性，探讨了有机硅疏水材料改良黄土渗透性的效果，并从微观角度分析了填方黄土在应力作用下渗透前后的微结构演变规律以及有机硅疏水材料的减渗机理。采用GeoStudio有限元软件模拟分析了延安新区某50m黄土填方体在不同降雨强度和地下水位抬升情况下的水分场变化。研究成果可为延安新区的黄土填方工程的建设提供理论依据。主要研究内容和成果如下：

（1）填方黄土的初始含水量越小，湿陷系数越大，低初始含水量（<15%）黄土的浸水压力越大，湿陷系数也越大。低干密度（1.35g/cm³）填方黄土具有较强的湿陷性，而高干密度（1.65g/cm³）填方黄土在高应力条件（>800kPa）下才会发生轻微湿陷。在高应力条件（>600kPa）下，增湿会引起填方黄土发生显著的湿陷变形。

（2）当应力和干密度增大时，填方黄土的饱和渗透系数显著减小，填方黄土在200kPa应力作用下，其饱和渗透系数下降80%以上。黄土的持水能力随应力和吸力的增大而显著降低。填方黄土在应力作用下的非饱和渗透曲线符合幂函数的变化规律。在应力作用下，土体孔隙分布特征发生改变，由连通性较好的大孔隙（>20μm）转变为连通性较差的中孔隙（5-20μm）和小孔隙（0-5μm）。应力改变了填方黄土内部原有的渗透路径，从而影响了其渗透性。

（3）黄土的饱和渗透系数随有机硅掺量的增加呈指数形式下降。在低干密度（1.35g/cm³）条件下，掺入3%的有机硅后渗透系数降幅可达87%，而在高干密度（1.65g/cm³）下，2%掺量有机硅可将黄土的饱和渗透系数降低93%左右。有机硅疏水材料掺入黄土后填充了其孔隙结构，形成了非封闭型的疏水结构。另外，部分有机硅颗粒附着在土骨架表面，形成疏水薄膜。两者共同作用改善了黄土的渗透性。

（4）填方地表土体雨水的入渗深度会随着降雨量的增加而增加，但短时强降雨条件下的入渗深度反而有所减小。当填方挖填结合面存在开裂裂隙时，裂隙周围土体的增湿饱和范围会随着降雨强度的增大而扩大。有机硅在填方地表的减渗效果明显，填方土体含水量显著减少，入渗深度也明显降低。

（5）当地下水位抬升后，受地下水位线增湿效应的影响，黄土填方体的体积含水量高于其初始体积含水量。特别是在地下水位线以上10.0m的范围内，土体受到水分增湿的影响最为明显，然后随着高程的增加逐渐减弱，呈现出一种“台阶状”分布。填方土体的体积含水量随着与水位线距离的增大呈现出先迅速减小后缓慢减小的趋势。地下水位的抬升对黄土填方水分场影响不容忽视，填方工程设计应充分考虑地下水位抬升的影响，以确保填方的稳定和安全运营。

In recent years, the ultra-deep loess filling project has become an effective means to expand urban space in the northwest loess gully region. However, the post-construction internal water field rebalancing process of the ultra-deep loess gully filling has a crucial impact on its infiltration and post-construction settlement development. At present, the research on the permeability characteristics of the fill is mainly focused on the migration paths such as surface water infiltration and local capillary water rise, and the influence of soil stress state on the permeability characteristics is rarely considered. For the ultra-deep loess filling project with large filling thickness, the influence of stress on its permeability characteristics is a key factor that must be considered in the study of groundwater field rebalancing process.

In this paper, the filled loess in Yan 'an New Area is taken as the research object. Through field investigation, laboratory test, theoretical analysis and numerical simulation, the consolidation collapsible deformation law and permeability characteristics of filled loess under hydro-mechanical coupling are studied. The effect of silicone hydrophobic powder on improving loess permeability is discussed. The microstructure evolution of filled loess before and after infiltration under stress, and the mechanism by which silicone hydrophobic powder reduces infiltration, are analyzed from a microscopic perspective. GeoStudio finite element software was used to simulate and analyze the water field changes of a 50 m loess fill in Yan 'an New Area under different rainfall intensity and groundwater level uplift. The research results can provide theoretical basis for the construction of loess filling project in Yan 'an New Area. The main research contents and results are as follows :

(1) The smaller the initial water content of the fill loess, the larger the coefficient of wet subsidence, and the larger the infiltration pressure and the larger the coefficient of wet subsidence of the low initial water content (<15%) loess. Low dry density (1.35g/cm³) fill loess has strong wetting subsidence, while high dry density (1.65g/cm³) fill loess will only have slight wetting subsidence under high stress conditions (>800kPa). Under high stress conditions (>600kPa), humidification causes significant wetting deformation of the fill loess.

(2) The saturated permeability coefficient of fill loess decreases significantly when the stress and dry density increase, and the saturated permeability coefficient of fill loess decreases by more than 80 per cent under 200 kPa stress. The water holding capacity of loess decreased significantly with the increase of stress and suction. The unsaturated permeability curve of fill loess under stress is in accordance with the change rule of power function. Under stress, the pore distribution characteristics of the soil changed from large pores (>20μm) with good connectivity to medium pores (5-20μm) and small pores (0-5μm) with poor connectivity. The stress changes the original infiltration path inside the fill loess, thus affecting the permeability of the fill loess.

(3) The saturated permeability coefficient of loess decreased exponentially with increasing silicone hydrophobic powder dosage. At low dry density (1.35g/cm³), the permeability coefficient decreased by up to 87% with 3% silicone hydrophobic powder doping, while at a dry density of 1.65 g/cm³, 2% silicone doping reduced the saturated permeability coefficient of loess by about 93%. The incorporation of silicone hydrophobic powder into loess fills its pore structure and forms a non-closed hydrophobic structure. Additionally, some silicone hydrophobic powder particles adhere to the soil skeleton surface, forming a hydrophobic film. The combined action of the two improved the permeability of loess.

(4) The infiltration depth of soil rainwater increases with the increase of rainfall, but the infiltration depth decreases under the condition of short-term heavy rainfall. When there are cracks in the excavation-filling joint surface, the wetting saturation range of the soil around the cracks will expand with the increase of rainfall intensity. The infiltration reduction effect of silicone on the fill surface is obvious, the water content of the fill soil is significantly reduced, and the infiltration depth is also significantly reduced.

(5) When the groundwater level is raised, the volumetric water content of the loess fill body is higher than its initial volumetric water content due to the humidification effect of the water table line. Especially in the range of 10.0m above the water table line, the soil body was most obviously affected by the humidification effect, and then gradually weakened with the increase of elevation, showing a ‘step-like’ distribution. The volumetric water content of the fill soil body shows a trend of rapid decrease and then slow decrease with the increase of the distance from the water table line. The influence of groundwater level rise on the water field of loess fill should not be neglected, and the design of fill project should fully consider the influence of groundwater level rise to ensure the stability and safe operation of fill.