不同土壤转换函数预测砂土非饱和导水率的对比分析

以现有的4种土壤转换函数(Pedotransfer Functions, PTFs)(包括ROSETTA、RAWLS、CAMPBELL和VAUCLIN)为例,将其用于土壤水力性质数据库UNSODA中56个典型砂土样本的非饱和导水率预测,对4种PTFs的预测结果进行了误差分析,探讨了饱和导水率对非饱和导水率预测的影响。结果表明,当同种PTFs预测的饱和导水率作为输入时,在4种PTFs中VAUCLIN的预测精度最高,其次为ROSETTA和RAWLS,CAMPBELL的误差最大;当实测饱和导水率作为输入时,RAWLS、CAMPBELL和ROSETTA的预测精度有了不同程度提高,但VAUCLIN的预测误差反而有所增大;饱和导水率对非饱和导水率预测的影响较大,实测饱和导水率作为输入时CAMPBELL预测的非饱和导水率与实测值最为接近。     

多孔介质非饱和导水率预测的分形模型

多孔介质非饱和导水率是地下水污染预测与评价的重要参数。根据分形几何的基本原理和方法,推导出了与Campbell经验公式在形式上完全一致的多孔介质非饱和导水率的预测公式。公式中的幂指数为介质孔隙分维和随机行走分维的函数,分别体现了多孔介质的静态性质与动态性质对其中水分运动的影响,但静态性质的影响是主要的,即导水率主要受多孔介质的结构控制。根据文献中报道的大量数据,利用笔者推导的预测公式计算得到的幂指数的统计值与试验测定的幂指数的统计值基本一致,说明推导的理论公式预测多孔介质非饱和导水率是较为可靠的。     

混合型缓冲回填材料非饱和水分扩散试验研究

设计了专门的浸水试验装置,测定了膨润土-石英砂混合物在非膨胀条件下吸水引起的水分分布及膨胀应力变化,研究了混合型缓冲回填材料非饱和水力学性质。试验结果表明,干密度约1.70 g/cmP3、掺砂率为30%的GMZ001膨润土-砂混合物的水分扩散系数与含水率的关系呈U型变化,即随着含水率增加,汽态水分扩散系数减小,液态水分扩散系数增大。根据理论推导建立非饱和导水率估算方程。计算发现,混合物的非饱和导水率随含水率的增大而增大。其中,汽态水分非饱和导水率先增大后略有减小,液态水非饱和导水率始终增大。试验发现,试样吸水后干密度趋于均匀化,试样内部不同位置的应力发展与水分迁移过程密切相关：渗入端的应力在入渗初期增长很快,随后减慢;渗出端的应力持续稳定增长;入渗96 h后,两端应力趋于一致。估算出的水分扩散系数及非饱和导水率,可用于评价混合型缓冲回填材料阻隔核素迁移安全性。     

包气带增厚区土壤水力参数及其对入渗补给的影响

为探讨包气带深部增厚区土壤水力参数变化对入渗补给过程的影响,采用压力膜仪对河北正定深部包气带(8.0~21.0 m)10个原状土样进行水分特征曲线测试,利用RETC软件中Mualem-van Genuchten导水率模型对其拟合,获取含水率与非饱和导水率的关系曲线,并根据达西法对其进行分析讨论.结果表明:场地包气带深埋区的非饱和导水率为25~240 mm/a.当某一埋深历史水位下降速度越快,该埋深处相同含水率情况下土壤非饱和导水率越大,说明对应土层的入渗补给强度越大;因包气带厚度增大使原来位于饱水带的层状非均质土层转变为包气带,潜水位波动下降过程中深部包气带土层因排水压密作用,使得土壤水力特性发生变化,进而影响垂向入渗补给过程.      

非饱和土壤特性参数获取方法

土壤水分特征曲线和非饱和导水率是研究包气带中水分贮存和运动的基本内容，也是确定放射性核素在饱气带中迁移规律的重要参数，本文介绍了在ＣＩＲＰ某野外试验场从地表到潜水位２８ｍ范围内４６个土样的土壤水分特征曲线的测量方法和其它土壤特性参数获取方法。     

邯郸地区土壤水入渗规律实验及数值模拟方法研究

在对土壤入渗理论进行总结和分析的基础上,依据邯郸市平原区的水文水情的基本特点,选定2~3处地点进行实验,完成了静态数据的收集和动态数据的观测,确定了实验区土壤质地类型、土壤容重等物理特性,结合实验测定的饱和导水率K、土壤水分特征曲线θ（ h）推算非饱和导水率K（θ）、扩散率 D（θ）等土壤水分运动参数。运用上述数据对Van Genuchten模型加以改进,并运用改进后的模型对实验中的水分变化过程进行数值模拟。结合实测成果和数值模拟成果,对邯郸市平原区已选定实验点土壤水入渗规律进行分析。     

非饱和流节点间导水率估计及达西平均分析

针对由Gardner-Russo函数描述的特征土壤,在双饱和度坐标系中,探讨了常规节点间导水率估计与量纲一水平达西平均(k*_H)和量纲一垂直达西平均(k*_V)的差异.k*_H是相邻两节点饱和度的函数,而k*_V也是空间步长(Δx)和特征参数(α)的函数.对水平非饱和流,算术平均高估导水率,而几何与调和平均低估导水率;从相对误差空间分布看,几何平均优于算术和调和平均.对垂直非饱和流,随Δx(或α)的增大,常规估计的相对误差空间顺(或逆)时针旋转并缩小,从而降低模型准确性.k*_H等值线具有对称性,而k*_V不具对称性;仅当Δx或α足够小时,k*_H才趋近于k*_V.因此,为提高非饱和流数值模拟的准确性,必须采用精确的达西平均来计算节点间导水率.     

充填结构包气带水分运动参数试验研究

煤炭开采引起大面积沉陷,利用粉煤灰或煤矸石作为充填介质,并覆盖一定厚度土壤的方法进行土地复垦是一种重要的充填模式。以粘质土壤、粉煤灰、煤矸石为研究对象,采用室内试验方法分别测定其物质的水分特征曲线、非饱和导水率曲线、容水度、水分扩散度等充填结构包气带的水分运动参数,为研究土壤-粉煤灰、土壤-煤矸石充填结构包气带水分运动规律提供参考依据。     

探讨变雨强条件下的入渗过程及影响因素

以积水条件下Green-Ampt入渗模型为基础,拓展其在变雨强中入渗率和累积入渗量计算形式。结合上述理论基础,选用饱和-非饱和土壤水、热和溶质运移模拟软件Hydrus-1D,探讨了常降雨与变雨强的入渗差异和饱和导水率、土壤类型对变雨强入渗过程的影响。研究表明：相对于常降雨,变雨强更利于雨水入渗,累积入渗量显著增加;其他水力参数不变,饱和导水率越大,入渗率与变雨强随时间变化曲线重合率越高,雨强控制时间越长,累积入渗量相应也越大;其他水力参数作用效果不容忽视,其影响作用可与饱和导水率达到相似效果。正确了解变雨强下入渗过程及影响因素,有助于准确地把握实际降雨入渗情况,对指导水力工程有重要的实际意义。     

非饱和黄土非线性K-G模型试验研究

K-G模型较之E-μ模型有较好的优越性,每个参数都能与土的剪切模量或体变模量直接联系,便于岩土工程的非线性理论和计算分析。以西部甘肃永登非饱和黄土为研究对象,进行大量不同湿度下的非饱和黄土常规三轴试验,获得不同初始饱和度下的K-G模型参数,进一步研究这些参数随初始饱和度的变化规律,建立模型参数和初始饱和度的相关表达式。在实际工程中,用测得的非饱和黄土的湿度指标,就可以得到黄土的K-G模型参数进行非饱和黄土的增湿数值模拟计算分析,避免吸力的量测和计算,具有一定的工程实际应用价值。     

基于连续分形理论的土壤非饱和水力传导度的研究

土壤的孔隙是具有连续分形性质的物理结构,根据土壤孔隙分形结构建立了非饱和水力传导度模型。模型包括综合系数、分形维数和临界体积比3个参数,综合系数为不同土壤基质势对应的非饱和水力传导度与饱和传导度之间的水力联系,与土壤质地有关;分形维数反映土壤孔隙结构对于非饱和水力传导度的作用,土壤不同尺寸孔隙之间的连通性则通过临界体积加以描述。模型具有较为明确的物理解释。将模型应用于5种不同土壤的结果表明,所提出的非饱和水力传导度模型具有较好的模拟效果。     

非饱和成都黏土瞬时剖面法渗透性试验研究

非饱和渗透系数是土体渗流分析的基础,成都黏土作为一种典型的非饱和膨胀土,具有吸水膨胀、失水收缩的特性,在受侧限的浸水过程中,土颗粒的膨胀致使孔隙体积减小,渗透性降低,使得直接对其进行非饱和渗透试验十分困难。根据瞬时剖面法的原理,利用EC-5土壤水分传感器测含水率、MPS-2电介质水势传感器直接同步测量同一位置的基质吸力,通过水平渗透试验研究了非饱和成都黏土在侧限条件下的渗透性。含水率和基质吸力的同步测量,保证了其测试条件的一致性,避免了采用其他土水特征曲线的影响。试验表明,试样的非饱和渗透系数为（1.33×10-11~3.14×10-9）m·s-1,非饱和渗透系数与基质吸力并非单调线性关系。基质吸力较高时,受膨胀土颗粒吸水膨胀的影响,渗透系数未出现明显变化,基质吸力降低到一定程度后,渗透系数快速增大。试验结束时土体已接近饱和,土中气体排出较慢,过水断面增加缓慢,促使渗透系数仍然持续增大。采用VG模型拟合k-s曲线,拟合参数α=0.048 kPa-1,n=1.79,m=0.48,试验结果可以用于成都黏土地区的渗流分析。     

三峡库区黄土坡滑坡非饱和水力参数研究

非饱和水力参数在计算滑坡降雨入渗过程与稳定性时是至关重要的材料参数。在三峡库区黄土坡滑坡上进行双环渗透试验,获取黄土坡滑坡表土层的饱和渗透系数。对黄土坡滑坡表土层的含水率和基质吸力进行实时监测,采集了黄土坡滑坡表土层中含水率和基质吸力随时间的变化数据,采用van Genuchten土-水特征曲线模型拟合了4个实时监测剖面的土-水特征曲线及其拟合参数。将饱和渗透系数与土-水特征曲线拟合参数代入van Genuchten渗透系数函数模型,求出了黄土坡滑坡表土层在非饱和条件下的渗透系数函数,为黄土坡滑坡在降雨作用下的稳定性计算提供了可靠的水力参数     

Influence of Unsaturated Soil Properties Uncertainty on Moisture Flow Modeling

The quality of a numerical modeling solution of moisture flow through unsaturated soil, in part, depends on properly described unsaturated soil properties. The variability of the Soil Water Characteristic Curve, SWCC, is attributed to hysteresis and reproducibility of measurement. Because the unsaturated conductivity function is rarely directly measured, the variability of the unsaturated soil hydraulic conductivity function is attributed to the uncertainty associated with the estimation of this parameter with currently available fitting functions, and hence a range of reasonable variation was considered. One-dimensional modeling of expansive soil under dry initial conditions (suction of 1,500 kPa) was performed; both potential evaporation and infiltration boundary conditions were considered. It was found that small variations in the unsaturated soil hydraulic conductivity function result in significantly different modeling outputs, as expected, while substential variation in SWCC alone (assuming the same unsaturated soil hydraulic conductivity for all SWCCs) produced almost identical soil response in terms of soil suction when the slope of the SWCC is similiar. Thus, proper characterization of the slope of the SWCC is important to proper suction profile determination.     

Fractal models for predicting soil hydraulic properties: a review

Modern hydrological models require information on hydraulic conductivity and soil-water retention characteristics. The high cost and large spatial variability of measurements makes the prediction of these properties a viable alternative. Fractal models describe hierarchical systems and are suitable to model soil structure and soil hydraulic properties. Deterministic fractals are often used to model porous media in which scaling of mass, pore space, pore surface and the size-distribution of fragments are all characterized by a single fractal dimension. Experimental evidence shows fractal scaling of these properties between upper and lower limits of scale, but typically there is no coincidence in the values of the fractal dimensions characterizing different properties. This poses a problem in the evaluation of the contrasting approaches used to model soil-water retention and hydraulic conductivity. Fractal models of the soil-water retention curve that use a single fractal dimension often deviate from measurements at saturation and at dryness. More accurate models should consider scaling domains each characterized by a fractal dimension with different morphological interpretations. Models of unsaturated hydraulic conductivity incorporate fractal dimensions characterizing scaling of different properties including parameters representing connectivity. Further research is needed to clarify the morphological properties influencing the different scaling domains in the soil-water retention curve and unsaturated hydraulic conductivity. Methods to functionally characterize a porous medium using fractal approaches are likely to improve the predictability of soil hydraulic properties.     

荒漠地区生物土壤结皮的水文物理特征分析

通过室内压力陶土板系统测定土壤含水率与基质势的关系与Star-1土壤水分物理特征测定系统确定非饱和土壤水力传导度的方法,结合应用van Genuchten公式模拟,分析了位于腾格里沙漠东南缘包兰铁路沙坡头段人工生态防护体系生物土壤结皮的水文物理特征,确定了其水分特征曲线、非饱和土壤水力传导度、非饱和弥散系数,并与原始沙丘沙进行比较。结果表明,生物土壤结皮的持水能力是沙丘沙的3~9倍。当土壤基质势在-1~-3 000 cm的较高范围变化时,生物土壤结皮平均非饱和水力传导度低于沙丘沙(约为12%);而当土壤基质势在-3 000~-15 000 cm的较低范围变化时,沙丘沙的平均非饱和水力传导度又大大低于生物土壤结皮(约为91.0%)。正是由于生物土壤结皮特殊的质地与结构,使其非饱和水力传导度随着土壤基质势的降低,以及土壤含水量的减少,而趋于增大。与原始沙丘沙比较,生物土壤结皮独特的水文物理特点决定了它对荒漠地区土壤微生境的改善与促进作用,特别是通常情况下的高持水能力与低土壤基质势条件下的较高非饱和水力传导度,能够提高浅层土壤水分的有效性,有利于人工生态防护体系主要组分浅根系灌木、草本植物与小型土壤动物的生存繁衍。     

Effect of soil hydraulic properties model on slope stability analysis based on strength reduction method

Soil hydraulic properties models which have been proposed were derived based on the empirical fitting curve such as Brooks-Corey model (BC) and Van Genuchten model (VG), or based on soil pore radius distribution such as Lognormal model (LN). Each model has different accuracy for predicting soil moisture distribution. In the analysis of rainfall-induced slope failure, the soil hydraulic properties model was needed to describe the physical phenomena of behavior characteristic of water in unsaturated soil. As moisture content has an effect on soil strength, it is vital to select the suitable soil hydraulic properties model for predicting Factor of Safety (FOS) especially in forecasting landslide hazard. In this study, a numerical model of seepage finite element analysis using BC, VG, and LN model were used and compared in order to analyze the soil moisture distribution, water movement phenomenon, and slope stability characteristic in unsaturated soil slope based on the strength reduction method (SRM). The results showed that the variations of the parameters predicting the moisture content of soil leads to differences of FOS in some cases. The parametric study showed that for the unsaturated soil condition, BC model has the greatest FOS value than the other model, while VG model has the lowest. On the other hand, the FOS of all models have the same result for the saturated condition. Other than that, it was found that the increasing of ESP value in the surface layer has significant effect in the sub-surface layer.     

Evaluation of probabilistic flow in two unsaturated soils

A variably saturated flow model is coupled to a first-order reliability algorithm to simulate unsaturated flow in two soils. The unsaturated soil properties are considered as uncertain variables with means, standard deviations, and marginal probability distributions. Thus, each simulation constitutes an unsaturated probability flow event. Sensitivities of the uncertain variables are estimated for each event. The unsaturated hydraulic properties of a fine-textured soil and a coarse-textured soil are used. The properties are based on the van Genuchten model. The flow domain has a recharge surface, a seepage boundary along the bottom, and a no-flow boundary along the sides. The uncertain variables are saturated water content, residual water content, van Genuchten model parameters alpha (α) and n, and saturated hydraulic conductivity. The objective is to evaluate the significance of each uncertain variable to the probabilistic flow. Under wet conditions, saturated water content and residual water content are the most significant uncertain variables in the sand. For dry conditions in the sand, however, the van Genuchten model parameters α and n are the most significant. Model parameter n and saturated hydraulic conductivity are the most significant for the wet clay loam. Saturated water content is most significant for the dry clay loam. Electronic Publication     

宏观水力传导度及弥散度的确定方法

根据非饱和水力传导率野外试验的统计数据,利用由随机理论推求的宏观水力传导率、宏观水分特征曲线、宏观弥散度的计算公式,计算了介质的宏观参数,为区域非饱和水分运动和溶质运移问题的分析和预测奠定了基础.