Effect of extreme acid and alkali treatment on pore properties of soil samples

Samples of six Polish and three Korean soils were acidified and alkalized with elevated concentrations of hydrochloric acid or sodium hydroxide from 0.001 to 1 mol dm^—3. The pore system of the studied soils was investigated using mercury intrusion (”︁macropores”) and water vapor adsorption (”︁mesopores”) experiments. The characteristics of the pores and their surfaces were very sensitive against acid and alkaline treatments. The macropore volume and radii increased in general with increasing of the concentrations of the treatment solutions. The macropore surface of all the clay rich soils exhibited a fractal behavior. The ranges of fractal scaling differed for particular soils. Macropore surface fractal dimensions changed under both treatments. For a given soil, the macropore fractal dimensions changed in the same direction under the effect of acid as under alkali. Both treatments decreased the mesopore volumes of Polish and increased the mesopore volumes of Korean soils. However, this was not true for two of Korean soils after extreme alkali treatments. In general, the average mesopore radius increased under lower treatments concentrations and decreased under higher concentrations. The mesopores were also fractal. The range of their fractal scaling was different for the Polish and Korean soils and roughly the same within each group. The fractal dimension of the mesopores decreased after acid treatment showing a smoothing of the material porous surface. Alkaline treatment affected the mesopore fractal dimension to a lower extent. A slight rise of the mesopore fractal dimension was noted in most cases.<?show $6#>     

Water storage,surface, and structural properties of sandy forest humus horizons

In this paper, we tried to find interrelations between water retention properties, surface characteristics, and structural features of sandy soils rich in organic matter. Raw humic, epihumic, and endohumic horizons of four acidic sandy forest soils were selected for this study. Specific areas and water adsorption energies were estimated from water vapor adsorption isotherms, micropore (nanometer range) parameters from desorption isotherms, mesopore (micrometer range) parameters from mercury intrusion porosimetry, and macropore (millimeter range) parameters from water retention curves measured using combined suction plate and pressure chamber methods. In the studied soils, pore volumes in all pore ranges were proportional to soil organic matter content. Thin column wicking technique was used to determine migration velocity vs. time dependence in the samples beds for a range of liquids of various surface tensions. From these dependencies the surface free energy and its components were estimated that were used for calculation of water contact angles and forces of interparticle interaction via a water meniscus. The dominant interactions in the studied soils were dispersive Lifshitz‐Van der Waals forces. In the two upper horizons polar acid‐base interactions were absent, however in the deepest horizons, high input of polar interactions occurred, due practically to electron‐donor component of the surface free energy. The electron‐acceptor contribution was low. The wettability of the soils was low in upper horizons as indicated by high water contact angles.     

The relation between silty soil structures and their mercury porosimetry curve counterparts: fractals and percolation

Mercury porosimetry data can be interpreted in terms of soil structure using ideas drawn from (i) network modelling and percolation theory and (ii) fractal geometry. We linked mercury intrusion to soil structure quantified by image analysis within a relevant common pore radius scale. We compared (i) three independent methods for computing fractal dimensions of the matrix and of the solid–pore interface, namely fitted square boxes method and pore chord distribution on scanning electron microscope images of soil thin sections, and mercury porosimetry, and (ii) two independent methods for characterizing pore connectivity (image analysis) and percolation process (pressure threshold from mercury porosimetry). The results from analyses of the pore size distribution by mercury porosimetry differed from those from the image analysis. Mercury intrusion is controlled by both the connectivity of the pore space network and locally by pore throats leading to larger pore bodies. By contrast, image analysis is unaffected by pore connectivity and measures pore bodies. On the other hand, the chord length method might not adequately capture the scaling properties of the solid–pore interface, whereas the mercury porosimetry data were also difficult to interpret in terms of fractal geometry because of the effects of pore connectivity. However, fractal dimension values of both the solid phase and the solid–pore interface increased as a function of clay content, whereas both percolation probability values and throat radius values at the mercury percolation threshold decreased. The results show the merit of applying both fractals and percolation theory for determining structural parameters relevant to mercury and water transport in soil.     

Surface fractal dimension of thermally treated peat soils from adsorption isotherms of nitrogen

Adsorption isotherms of nitrogen at 80 K were measured on thermally modified peat soils. The isotherms were used to evaluate the surface fractal dimension from the Frenkel‐Halsey‐Hill equation. We also tested if surface characteristics were correlated to the water holding capacity index, which characterizes the degree of the secondary transformation of peat soils. In most cases the thermal treatment lowered the value of the surface fractal dimension, i.e. diminished the roughness of the part of the surface that adsorbs nitrogen molecules.     

岷江上游干旱河谷土壤粒径分布分形维数特征

具有分形特征是土壤的客观属性之一,为了探讨分形维数与土壤性质之间的关系与影响因素。运用土壤体积粒径分布分维模型计算了岷江上游干旱河谷不同土地利用方式下土壤表层(0～20cm)161个样品的分形维数,分析了分形维数的空间变化特点及其与粒度组成、有机质和土壤养分之间的相关性。土壤粒径分布分形维数可以作为表征土壤结构和性质的重要指标。结果表明:不同土地利用方式下土壤的粒径分布具有不同的分形特征,分形维数在2.5011～2.7825之间,粉壤土>壤土>砂壤土,耕地大于灌林地。土壤颗粒体积分形维数与黏粒(<0.002mm)和粉粒(0.002～0.05mm)的体积百分含量以及土壤全钾含量呈极显著正相关关系,与砂粒(>0.05mm)的体积百分含量呈极显著负相关关系,而与土壤有机质,全氮,全磷,速效磷和速效钾含量的相关性未达到显著水平。研究结果可以为研究区植被恢复和土地利用开发提供一定的依据。     

Effect of leaching of DOC on pore characteristic of a sandy soil

Changes of microstructural properties of a sandy soil from a former sewage farm due to the leaching of dissolved organic carbon (DOC) were studied. The leaching of DOC at various pH values was induced using sodium hydroxide or hydrochloric acid solutions. The removal of DOC altered the pore properties of the remaining solid. The average pore radius measured from water vapor desorption isotherms (micropores range) increased with the increase of the removed DOC under alkaline conditions and did practically not alter under acid treatment. The average pore radius measured by the mercury intrusion porosimetry (mesopores range), decreases, however, for low amounts of the DOC extracted and increases on extracting higher DOC amounts. The mesopores appeared to be fractal. At moderate amounts of the DOC leached the finer mesopores occurred having the higher fractal dimensions than the coarser mesopores.     

Changes of surface, fine pore and variable charge properties of a brown forest soil under various tillage practices

Effects of 6 years no-tillage (NT), ploughing, disking and the two last treatments combined with loosening on surface area, water vapor adsorption energy, variable charge and fine pore properties of a brown forest soils were studied using water vapor adsorption–desorption, back-titration and mercury intrusion measurements. The studied soil properties altered markedly under mechanical tillage treatment as compared to NT soil. The radii and the volumes of cryptopores (sizes from 1 to a few tens of nanometers) decreased and the opposite was found for ultramicropores (sizes from a few tens of nanometers to around 10 μm). However, fractal dimension of cryptopores and ultramicropores had changed very slightly, indicating that general geometrical structure of the fine pore system in the studied range (ca 1 nm–10 μm) remained unaltered despite pore size-shift. Surface areas and the amount of variable surface charge were markedly lower in mechanically tilled soil. A decrease of organic matter content was observed as well. Decrease of water vapor adsorption energy and increase of the fraction of strongly acidic surface functional groups accompanied mechanical tillage treatments.     

Effect of humic acids,sesquioxides and silica on the pore system of silt aggregates measured by water vapour desorption,mercury intrusion and microtomography

Most of the information on soil aggregation and porosity comes from studies of natural soil in which the effects of the different constituents that form the structure overlap. The aim of this research was to study the effects of these constituents separately on well‐characterized artificial aggregates in order to understand them better. To do this, the pore system of model silt aggregates, amended with different amounts of humic acids, iron and aluminium hydroxides or colloidal silica, was investigated at three levels of magnification with water vapour desorption (nanometre sizes), mercury intrusion (micrometre sizes) and microtomography (tens of micrometres). Humic acid and aluminium hydroxide increased aggregate porosities measured by all methods. An increase in porosity with increasing additions of each constituent was indicated only by water desorption. We did not observe any well‐defined trends in the dynamics of average pore radii. The pore surface fractal dimension determined by mercury intrusion was negatively correlated with that measured by water desorption. The pore system in granular media comprises larger voids joined by narrower necks; therefore, we attempted to relate their sizes with a novel approach that combined microtomography with mercury intrusion and extrusion data. We observed a decrease in the size of pore necks that give access to voids of the same sizes with increasing additions of all constituents. With additions of humic acid this effect was the smallest. The mercury intrusion data showed the formation of separate concretions of iron hydroxides and silica in silt aggregates.     

半湿润区长期施肥对土壤结构体分形特征的影响

利用黄土高原南部半湿润地区长达25年田间肥料定位试验020.cm土层土样,研究了长期不同施肥模式与土壤结构体大小、结构体分形特征与土壤肥力的相互关系。结果表明,长期不同施肥模式下土垫旱耕人为土结构体分形特征存在一定差异:7种施肥处理土壤结构体分形维数分布在2.4388～2.6363之间,其中以化肥+厩肥处理土壤结构体分形维数最大,不施肥土壤结构体分形维数最低,说明化肥与有机肥长期配施对土壤团聚体结构分布影响较大。相关分析发现,土壤结构体分形维数与5～2mm团聚体间具有极显著的正相关关系(r=0.994,P0.01);与土壤有机碳、全氮、硝态氮、有效磷含量均具显著正相关关系,与土壤碳氮比(C/N)呈显著负相关关系。在长期不同施肥模式下,分形维数对土壤性质变化的边际量亦有明显差异:土壤结构体分形维数每增加一个单位值,土壤有机碳、全氮、C/N、硝态氮和有效磷的变化依次为31.628%、2.404%、-6.014%、90.370%和172.760%。由边际分析可知,长期施肥条件下土壤结构体分形维数的变化对土壤有效磷、硝态氮的影响最大。     

土壤和润湿研究中的分形现象

分形几何学的理论与方法已被用于土壤表面不规则性、旋耕土块轮廓及表面裂纹形状和分布、土壤值的空间分布及固体表面润湿性的研究中,利用分形维数定量探讨它们的规律性。本文综合评述了土壤表面、土块轮廓与裂纹、土壤值及润湿研究中的分形特性。     

Scaling analysis of water retention curves for unsaturated sandy loam soils by using fractal geometry

Fractal geometry was deployed to analyse water retention curves (WRC). The three models used to estimate the curves were the general pore‐solid fractal (PSF) model and two specific cases of the PSF model: the Tyler & Wheatcraft (TW) and the Rieu & Sposito (RS) models. The study was conducted on 30 undisturbed, sandy loam soil samples taken from a field and subjected to laboratory analysis. The fractal dimension, a non‐variable scale factor characterizing each water retention model proposed, was estimated by direct scaling. The method for determining the fractal dimension proposed here entails limiting the analysis to the interval between an upper and lower pressure head cut‐off on a log‐log plot, and defining the dimension itself as the straight regression line that interpolates the points in the interval with the largest coefficient of determination, R². The scale relative to the cut‐off interval used to determine the fractal behaviour in each model used is presented. Furthermore, a second range of pressure head values was analysed to approximate the fractal dimension of the pore surface. The PSF model exhibited greater spatial variation than the TW or RS models for the parameter values typical of a sandy loam soil. An indication of the variability of the fractal dimension across the entire area studied is also provided.     

Water retention characteristics of soils with double porosity

A soil with double porosity is modelled as a collection of aggregated particles, in which a single aggregate is made up of discrete particles bonded together. Separate fractal distributions for pore sizes around and within aggregates are defined. The particle size distribution of the double porosity soil is also modelled using a fractal distribution, which may have a fractal dimension very different to those defining the pore sizes. The surface areas of the particles and the pores within the aggregates are assumed to be equal, enabling an expression linking two fractal dimensions to be defined. It is necessary to introduce ratios between maximum and minimum particle and pore sizes into the expression. A theoretical soil‐water characteristic curve is then derived for a double porosity soil. The curve, and the underlying assumptions regarding the distributions of pore and particle sizes, showed good agreement with experimental data for a range of soils having double porosity. A discontinuity is observed in the soil‐water characteristic curve at a second air entry value related to the maximum pore size within the aggregates, a feature also observed in experimentally obtained soil‐water characteristic curves for double porosity soils.     

沙漠非饱和风沙土壤水分特征曲线预测的分形模型

应用VanGenuchten提出的土壤水分特征曲线公式,推导出了沙漠风沙非饱和土壤水分特征曲线的分形模型。通过对古尔班通古特沙漠地9种不同土壤样本利用中子水分仪和负压计实测的水分特征曲线资料反求得到相应的分形维数,分析了分形维数与土壤质地之间的关系,结果表明随着土壤质地从流动风沙土、半固定风沙土到固定风沙土的变化,其分形维数呈逐渐增大。此外,基于土壤颗粒的重量与粒径分布求出了古尔班通古特沙漠地风沙土壤粒径的分形维数。通过对土壤水分特征曲线的分形维数与土壤粒径的分形维数的对比,得知它们之间存在着良好的线性关系。根据此关系,利用易测得的土壤粒径分形维数结合所推导的分形模型,对土壤水分特征曲线进行了预测,模型的预测结果很好地吻合了实测的土壤水分特征曲线。这一结果对于实际工作中根据风沙土壤颗粒大小分布的分形维数来预测沙漠风沙土壤水分特征曲线具有一定的指导意义。     

Pore‐system characteristics of pavement seam materials of urban sites

The original light‐brown sandy seam filling of pavements in urban areas turns dark and changes its properties by the time due to various inputs of urban dust. Deposited C_org inputs do mostly not have natural characteristics but are man‐made, e.g., diesel dust. Thus, properties of the seam material are not predictable from experiences with forest or agricultural soils. Semiperviously sealed urban areas are sites of contaminant deposition as well as groundwater recharge. For an assessment of the resulting groundwater‐contamination risk in these areas, the properties of the seam material, which influences transport processes, must be known. The aim of this study was to investigate the pore‐system build‐up, which includes size distribution and fractal character in the seam material of urban sites. The investigated samples were taken from pavements adjacent to roads in Berlin and Warsaw. The micropore parameters (nanometer range) were characterized using water‐vapor desorption isotherms, mesopore parameters (micrometer range) were estimated from mercury‐intrusion porosimetry and macropore parameters (millimeter range) from water‐retention curves. Particle density, dry bulk density, and particle‐size distribution were measured using standard methods. Volumes of micro‐ and mesopores as well as particle densities and dry bulk densities correlated with C_tot contents. However, no such relation was found for macropore volumes. Compared to the original sandy seam filling, the altered seam material shows significantly higher C_org contents and higher amounts of micro‐ and mesopores. Therefore, the available water capacity increases by 0.05–0.11 m³ m^–3, as compared to the original sandy seam filling. Compared to natural sandy soils having similar C_org contents, the seam material shows similar macropore volumes, but the volume of mesopores and micropores is a few times smaller. That is mainly because of the particulate character of the organic matter.     

土壤颗粒的分形特征及其应用

本文应用土壤颗粒的质量分布原理来描述土壤颗粒的分形特征。通过对10种土壤颗粒的机械组成进行分析,分别计算出它们的分形维数（D=2.489～2.896）,并分析了其与土壤质地之间的关系。同时对土壤颗粒分形维数与所对应土壤的幂函数型水分特征曲线的拟合分形维数进行比较分析,建立了二者之间的相关关系。结果表明:分形维数的大小反映了土壤质地中粘粒、粉粒和砂粒含量的变化,随粘粒含量的增多分形维数增大,随砂粒含量的增多分形维数减小;同时土壤颗粒分形维数与所对应的水分特征曲线的拟合分形维数呈现出良好的一致性,因而对所研究的土壤而言,可应用土壤颗粒的质量分形维数结合幂函数模型来估算土壤水分特性曲线。     

Dual-porosity modelling of the pore structure and transport properties of a contaminated soil

We have developed a new method to characterize the pore structure of mineral soils. We combined data from the analysis of back-scattered scanning electron microscope (BSEM) images of resin-impregnated pore-casts, and mercury intrusion porosimetry (MIP) data, with analytical percolation models and inverse modeling algorithms. The pore space is regarded as a dual-pore network consisting of a primary Euclidean pore-and-throat network and a secondary, fractal, pore system that is accessed through primary pores. The digitized 2-D BSEM images of resin-impregnated soil samples are employed to determine the autocorrelation function. The Fourier transform of this function provides the small-angle neutron scattering (SANS) intensity function, which is extended by using the surface fractal dimension obtained from high-pressure MIP data. Inversion of the extended scattering intensity function produces the volume-based radius distribution function of spherical pore bodies (PBRD). The complete volume-based PBRD is fitted with a composite number-based PBRD composed of a lognormal primary PBRD and a power (fractal) secondary PBRD with upper and lower cut-offs. Based on the concepts of invasion percolation, an analytic mathematical model that describes Hg intrusion into dual pore networks is developed. The complete PBRD and pore-throat radius distribution (PTRD) functions of the primary network along with the drainage accessibility functions (DAFs) of the primary and secondary pore networks are estimated with inverse modelling of the Hg intrusion curve. Based on critical path analysis of percolation theory, approximate analytical relationships are developed to calculate explicitly the absolute permeability and electrical formation factor from the geometrical and topological parameters of the primary pore network. The method is demonstrated with application to four soil samples.     

土壤短期吹蚀的粒度分维研究

基于风洞实验数据 ,对砂质壤土与壤质砂土短期吹蚀的粒度分形结构及其分维变化进行了探讨。结果表明 :( 1)在砂质壤土与壤质砂土的不同吹蚀时段 ,各自床面的粒度组成是具有分形结构特征的 ,在风洞里不同风速与时间下的吹蚀并未改变两种土壤所具有的分形结构 ,改变的只是分形结构的定量描述参数分维 ;( 2 )无论是在初始状态还是在一定的风速和时间下 ,砂质壤土的分维都小于壤质砂土的分维 ;( 3)两种不同质地的土壤在不同的吹蚀时段床面粒度分维与 <0 0 5mm的颗粒 (即粉粘粒 )含量之间都存在着显著的正相关性 ;( 4 )两种土壤在吹蚀的过程中由于土壤性状的差异 ,其床面粒度分维会随时间和风速的不同而出现相异的变化过程     

Structure and self-similarity in silty and sandy soils: the fractal approach

Soil structure was studied using the concept of fractals and related to soil texture and aggregate properties such as surface charges and aggregate stability. The mass and porosity fractal dimensions (D_m and D_p) of silty and sandy soils were determined on in situ soils using a variety of soil sections (thin, very-thin and ultra-thin), by image analysis on a continuous scale from m to 10^?9 to 10^?1m. Surface fractal dimensions (D_s) of these soils were determined on < 2 mm air-dried samples using mercury porosimetry and the fractal cube generator model. The results suggest that soils are not pore fractals but mass and surface fractals with D_m= 1.1 D_s when the dimension of the embedding Euclidean space d is 3. The soil structures could possibly be described by fractal diffusion-limited aggregation with complex interconnected aggregates or by fractal cluster–cluster aggregation models. As a preliminary conclusion, the fractal approach appears to be a potentially useful tool for understanding the underlying mechanisms in the creation or destruction of soil structure.     

土壤水分特征曲线的分形模拟

Many empirical models have been developed to describe the soil water retention curve （SWRC）. In this study, a fractal model for SWRC was derived with a specially constructed Menger sponge to describe the fractal scaling behavior of soil; relationships were established among the fractal dimension of SWRC, the fractal dimension of soil mass, and soil texture; and the model was used to estimate SWRC with the estimated results being compared to experimental data for verification. The derived fractal model was in a power-law form, similar to the Brooks-Corey and Campbell empirical functions. Experimental data of particle size distribution （PSD）, texture, and soil water retention for 10 soils collected at different places in China were used to estimate the fractal dimension of SWRC and the mass fractal dimension. The fractal dimension of SWRC and the mass fractal dimension were linearly related. Also, both of the fractal dimensions were dependent on soil texture, i.e., clay and sand contents. Expressions were proposed to quantify the relationships. Based on the relationships, four methods were used to determine the fractal dimension of SWRC and the model was applied to estimate soil water content at a wide range of tension values. The estimated results compared well with the measured data having relative errors less than 10% for over 60% of the measurements. Thus, this model, estimating the fractal dimension using soil textural data, offered an alternative for predicting SWRC.     

基于Menger海绵模型的煤矸石粉改良膨胀土微结构特征

为解决膨胀土对工程结构以及农业生态环境的危害，进行煤矸石粉改良膨胀土的试验研究。对煤矸石粉掺量为0、3%、6%、9%的膨胀土土样进行压汞试验，测得微观孔隙特征值；选取Menger海绵模型建立孔隙分分形模型，计算土体孔隙分形维数，探究土体孔隙分形维数与孔隙特征参数以及煤矸石粉掺量变化的关系。结果表明：随着煤矸石粉掺量增加，土中大孔隙所占的含量较素膨胀减少61.5%，孔隙类型从团粒间孔隙转化为颗粒间孔隙；煤矸石粉的掺入改变了土体的孔隙结构特征，煤矸石粉与膨胀土发生胶结反应，孔隙连通性降低，使得总孔隙体积、孔隙率、孔隙平均孔径、孔隙临界孔径等孔隙特征参数呈减小趋势；基于分形理论分析孔隙分形维数，分形维数随煤矸石粉掺量的增加而增加，且与孔隙特征参数呈显著相关性。孔隙分形维数反应了孔隙特征参数以及孔隙发育程度，为土的孔隙表征提供方法借鉴。