土壤非饱和导水率模型中参数的敏感性分析

针对邵明安根据再分布过程得出的非饱和导水率模型,对其中参数的敏感性进行分析,通过实测资料计算非饱和导水率对不同参数的敏感度,对比参数对非饱和导水率的影响程度。研究表明采用线性关系表示土壤湿润剖面的平均湿度和湿润锋处湿度之间的关系时,非饱和导水率对参数的敏感性比其他参数高得多。     

土壤饱和导水率空间预测的不确定性分析

当土壤转换函数应用于土壤水力性质估计时,对于预测值的不确定性往往容易被忽视。为了有针对性地提出减少这种不确定性的方法和措施,提高土壤转换函数的实际应用能力,以两种现有的土壤转换函数(Vereecken和HYPRES模型)为例,将其应用于山东省平度市土壤饱和导水率的空间预测,并利用拉丁超立方抽样(LHS)方法对预测结果的不确定性进行了分析。结果表明,饱和导水率空间预测的不确定性主要来源于土壤基本性质的空间插值误差和土壤转换函数自身的预测误差。当Vereecken模型应用于饱和导水率空间预测时,预测结果的不确定性主要由土壤基本性质空间插值误差所决定,土壤转换函数预测误差的影响较小,而HYPRES模型则是受二者的双重影响。     

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。     

土壤饱和导水率的多尺度预测模型与转换关系

运用联合多重分形方法研究不同土层土壤饱和导水率与土壤基本物理特性的多尺度相关性,建立不同土层土壤饱和导水率的多尺度预测模型,构建不同土层土壤饱和导水率之间的转换关系。结果表明:不同土层土壤饱和导水率与土壤基本物理特性的相关程度排序不同;在单一尺度和多尺度上,0~20 cm土层土壤饱和导水率与土壤基本物理特性的相关程度排序相同,20~40 cm土层土壤饱和导水率与土壤基本物理特性的相关程度排序不同;土壤饱和导水率多尺度预测模型的预测精度较高,0~20 cm土层和20~40 cm土层拟合值的均方根误差分别为0.035 0和0.029 0;0~20 cm土层和20~40 cm土层土壤饱和导水率转换关系的计算精度较高,拟合值的均方根误差为0.037 5。     

基于热力学基础上的非饱和砂土本构模型-理论研究

热力学是一种普适理论,因此非饱和砂土的变化过程必然也遵循热力学原理。利用热力学原理可以从更普遍的情况(条件)和更一般的视角审视非饱和土的水力-力学性质。本文基于热力学理论并考虑砂土的剪胀-各向异性以及塑性耗散之间的关系,建立固-液两相耦合的非饱和砂土本构模型的理论框架,更深入地揭示非饱和砂土复杂的行为和性质。     

无结构土壤非饱和水分函数解析

文中从土壤微观统计学角度出发，用各向均一无结构土壤切片孔径级配幂函数构建的统计平行毛管束模型，统一论证了水分统计分布与水分函数依含水率、土壤基质而变的机理和规律，给出了相应函数式和可操作的参数确定方法．把迄今水分函数研究的纯经验相关现状提高到理论分析水平，使建立理论公式成为现实。用文献［１］提供的Ｓａｒｐｙ壤土和Ｇｅａｒｙ粉壤土实验成果，对文中结论做了验证。     

非饱和土壤水力参数预测的分形模型

综述了利用分形几何理论,可在土壤水力性质,包括土壤水分特征曲线及水力传导系数与土壤结构分维之间建立起一定的函数关系式.这些函数关系式大多与Campbell定律具有相同或相似的幂定律形式,一方面揭示了Campbell定律的物理实质,另一方面可用于土壤持水量及水力传导系数的预测.     

土壤入渗特性的空间变异性及土壤转换函数

以在杨陵一级阶地上进行的入渗试验为基础,利用多重分形和联合多重分形方法,研究分析了土壤入渗特性在多尺度上的空间变异性及与土壤物理特性的相关性,并在此基础上建立了土壤入渗特性的土壤转换函数。研究表明:土壤入渗特性具有多重分形特征,观测尺度上,稳定入渗率、前30 min累积入渗量的空间变异都主要由粗粉粒和粘粒含量的空间变异造成。在多尺度上,稳定入渗率的空间变异受土壤容重、粗粉粒和粘粒含量的空间分布影响显著,前30 min累积入渗量的空间变异受粗粉粒和粘粒含量的空间分布影响显著,与观测尺度上的影响因素相同。基于联合多重分形分析建立的稳定入渗率的土壤转换函数的计算误差较小,前30 min累积入渗量的土壤转换函数的计算误差较大。     

黄土高原北部坡面尺度土壤饱和导水率分布与模拟

为探明黄土高原北部坡面土壤饱和导水率(K_s)空间分布特征,为土壤水文过程模拟与预测提供理论依据,采用经典统计学和地统计学的空间变异分析方法,分析了坡面尺度土壤K_s的空间变异特征,并用一阶自回归状态空间模型对K_s的空间分布进行了模拟.研究区坡面尺度K_s的变异为中等程度变异,具有中等程度空间依赖性,变程为42 m.K_s与容重、砂粒、粉粒和黏粒含量在不同滞后距离下均具有自相关关系和交互相关关系.容重和土壤颗粒是影响坡面K_s空间分布的主要因素.状态空间模拟结果表明,基于容重和土壤颗粒的状态空间方程可以很好地解释坡面K_s的变异状况(R2>0.9).一阶自回归状态空间模型可用于田间条件下坡面尺度K_s分布特征的预测.     

应用CT扫描研究非饱和砂土中污染物的迁移规律

应用CT扫描技术对两种稳定非饱和状态的砂土试样分层进行扫描,得到不同深度CT扫描层图像,采用Image J图像处理软件将CT图像转化为CT数均值,然后在稳定非饱和试样中分别间断性连续注入污染物KI溶液,测定不同时间间隔CT扫描图像,计算注入污染物先后扫描图像结果的差值,建立CT数均值和污染物迁移之间的关系,研究污染物在非饱和砂土中的运移特征,得出非饱和砂土中污染物浓度随时间和深度的变化规律,对研究其他介质中污染物的迁移具有重要的指导作用。     

Practical pedotransfer functions for estimating the saturated hydraulic conductivity

The saturated hydraulic conductivity k is one of the most important and widely used geotechnical parameters, commonly involved in a diversity of applications. The value of k depends on many factors, which can be divided into three classes: properties of the fluid, pore size distribution, and characteristics of the solid surfaces. Because the latter two are not necessarily constant within a given deposit, the hydraulic conductivity may vary significantly in space. Engineers and scientists need indications about how changing factors may affect the actual k value. In this paper, the authors propose some simple expressions, based on pedologic properties, to estimate the value of k. Using experimental results of their own and taken from the literature, it is shown that the proposed pedotransfer functions can be used for quickly estimating the k value for granular and plastic/cohesive soils. Such expressions can be employed, with a useful chart format, for the preliminary design phase of a project, and also for estimating the range of k values to be anticipated within a given deposit.     

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。     

随机单裂隙饱和/非饱和渗透系数研究

裂隙易在降雨作用下诱发滑坡等灾害,裂隙的饱和/非饱和渗透特性是研究此类问题的关键。利用精密数控机床制作随机粗糙裂隙面,并研制了一套仪器进行此随机粗糙裂隙的渗流试验,得到了裂隙的饱和渗透系数,然后通过间接方法预测此裂隙的非饱和渗透系数。研究发现,当裂隙平均开度为0.4 mm时,其饱和渗透系数为0.1 m/s。通过立方定律得到的水力等效隙宽为0.35 mm,小于其平均隙宽。同时裂隙的渗透系数与平均隙宽的平方成正比,这与立方定律的趋势相一致。研究得到了不同隙宽裂隙的非饱和渗透系数函数,当基质吸力小于进气值时,渗透系数为一常数,即为饱和渗透系数;当基质吸力大于进气值时,裂隙板的渗透系数急剧减小。当裂隙板的基质吸力达到其残余含水率对应的吸力值时,裂隙板的渗透系数基本稳定。在此情况下,基质吸力的继续增加对渗透系数的影响非常小,很难使渗透系数减小。     

A kinematic hardening based model for unsaturated soils considering different hydraulic conditions

At present, several of the existing elastoplastic constitutive models are adapted for describing the stress–strain behavior of unsaturated soils. However, most of them present certain limitations in this field. These limitations can be related to the basic model and/or added unsaturated state variables and formulations. In this regard, inability to model the hydro‐mechanical behavior in constant water (CW) conditions is an example of these limitations. In this paper, an advanced version of CJS model is selected for adaptation to the unsaturated states. Adaptation to unsaturated states is achieved in the framework of effective stress approach. Effective stress equation and unsaturated state variables are selected based on the recent research existing in the literature. The developed model is capable of describing the complex behavior of unsaturated soil in the CW condition in addition to predicting the behavior at failure and post–failure, nonlinear elastoplastic behavior at low levels of stress and strain (by selecting a very small elastic domain), as well as wetting and collapse behaviors. In order to validate the model, results of triaxial tests in CD and CW conditions are used. The validation results indicate the good capability of the proposed model. Behavior of the unsaturated soils during wetting is an important issue. For this reason, the model is also evaluated based on the results of wetting and collapse triaxial tests. A comparison between the tests and simulation results shows that the model is able to predict the soil behavior under the wetting path. Copyright © 2016 John Wiley & Sons, Ltd.     

Cavity expansion in unsaturated soils exhibiting hydraulic hysteresis considering three drainage conditions

Cavity expansion theory assists in the interpretation of in situ tests including the cone penetration test and pressuremeter test. In this paper, a cavity expansion analysis is presented for unsaturated silty sand exhibiting hydraulic hysteresis. The similarity technique is used in the analysis. The soil stress–strain behaviour is described by a bounding surface plasticity model. Results of oedometric compression tests, isotropic compression tests and triaxial shear tests for both saturated and unsaturated states are used to calibrate the model. The void ratio, suction, degree of saturation and effective stress are fully coupled in the analysis. The influence of where the initial hydraulic state is located on the soil–water characteristic curve on the cavity wall pressure is investigated and found to be significant. Also, the effects of three different drainage conditions (constant suction, constant moisture content and constant contribution of suction to the effective stress) on cavity wall pressure are studied. It is found that the drainage condition in which the contribution of suction to the effective stress is constant offers a good approximation to the other two. This may simplify interpretation of in situ tests. When testing occurs quickly, meaning a constant moisture content condition prevails, a constant contribution of suction condition can be assumed without loss of significant accuracy. The contribution of suction assumed in the interpretation can be taken as being equal to the in situ value, although this discovery may not be applicable to all soil types, constitutive models and soil–water characteristic curves. Copyright © 2015 John Wiley & Sons, Ltd.     

快速测量非饱和土渗透系数的湿润锋前进法适用性研究

非饱和土渗透系数函数是非饱和土体渗流分析中必不可少的参数。然而非饱和土渗透系数函数测量非常困难,其中稳态法测量范围过于狭小,而瞬时截面法耗时动辄数月,难以应用。为此,提出了湿润锋前进法,有望在一周内测得渗透系数函数。采用数值模拟手段检验湿润锋前进法的测量精度和适用范围。数值模拟结果显示：对于砂土、粉土、黏土,湿润锋前进法得到的渗透系数函数均与输入的理论渗透曲线一致,但测量范围限于高吸力范围（大于进气值）。此外,还采用瞬时截面法计算了渗透系数函数,结果表明：瞬时截面法计算的渗透系数在理论渗透曲线附近波动,其精度取决于监测截面的间距,间距越大,精度越低。在给出的20、60、100 mm这3种间距中,20 mm间距时计算得到的渗透系数精度最高,但与湿润锋前进法的精度仍有一定差距。因此,湿润锋前进法是一种可靠的能够快速得到渗透系数函数的测量手段。     

Determination of unsaturated hydraulic conductivity of sandy soils: a new pore network approach

Acta Geotechnica - Hydraulic conductivity is one of the most important characteristics of unsaturated soils. Its determination is essential for modeling various phenomena of interest such as...