植被根系对土体水力学特性影响的现状与定量分析

在全球气候变暖和“双碳”战略的背景下,植被护坡成为一种潜在的碳负排放边坡加固和侵蚀控制手段。植被根系的发育可以改变土体结构和水力学特性,进而影响边坡的稳定性。虽然一些试验研究已经探讨了特定条件下植被对土体水力学特性的影响,但是对于植被根系改变土体水力学特性的一般规律尚不清楚。该文从植被蒸腾作用、根系物理作用以及根系生物化学作用3个方面入手,收集并梳理了近年来国内外相关研究,分析并总结了植被根系改变土体水力学特性的作用机理,且对已有试验数据进行了统计分析。指出植被根系对土体水力学特性的改变取决于植被蒸腾、根系物理作用和根系生物化学作用三者的相对贡献,同时受根系类型、土体类型及生长阶段等因素的影响。因此,植被根系对土体水力学特性的影响十分复杂,更全面广泛的研究对于揭示植被护坡机理是亟需的。最后,探讨了植被根系影响土体水力学特性的研究空白和未来趋势。

Applying accurate gradients of seismic wave reflection coefficients (SWRC) to the inversion of seismic wave velocities

Through solving the Zoeppritz's partial derivative equations, we have obtained accurate partial derivatives of reflected coefficients of seismic wave with respect to Pand S-wave velocities.With those partial derivatives, a multi-angle inversion is developed for seismic wave velocities.Numerical examples of different formation models show that if the number of iterations goes over 10, the relative error of inversion results is less than 1%, whether or not there is interference among the reflection waves.When we only have the reflected seismograms of P-wave, and only invert for velocities of P-wave, the multi-angle inversion is able to obtain a high computation precision.When we have the reflected seismograms of both P-wave and VS-wave, and simultaneously invert for the velocities of P-wave and VS-wave, the computation precisions of VS-wave velocities improves gradually with the increase of the number of angles, but the computation precision of P-wave velocities becomes worse.No matter whether the reflected seismic waves from the different reflection interface are coherent or non-coherent, this method is able to achieve a higher computation precision.Because it is based on the accurate solution of the gradient of SWRCs without any additional restriction, the multi-angle inversion method can be applied to seismic inversion of total angles.By removing the difficulties caused by simplified Zoeppritz formulas that the conventional AVO technology struggles with, the multiangle inversion method extended the application range of AVO technology and improved the computation precision and speed of inversion of seismic wave velocities.

Assessment of Super Absorbent Polymer (SAP) on Plant Available Water (PAW) in Dry Lands

One of the ways of overcoming the cost of irrigation is through in-situ water harvesting at the plant roots. Super absorbent polymer (SAP) can facilitate water harvesting at the plant roots. This study attempted to assess the effect of SAP on plant available water (PAW) of different soils. In this study, SAP was sequentially added at the rate of 0.2%, 0.3% and 0.5% of the soil weight and its impact assessed in clay, sandy clay and sandy loam soils. The moisture retention characteristics of the original and SAP treated soils were studied using soil water retention curves (SWRC) and results modelled using Gardner model. PAW was estimated from SWRC as the difference between moisture content at 1.5 and 3 bar in all soils. The difference in PAW between original and treated soils was assessed at 5% level of significance. The WRC of all the samples was adequately found to be described by the Gardner model (Coefficient of determination R2 ≥ 98% and residual standard error (RSE) ≤ 0.04). SWRC changed with increase in SAP percentage in clay, sandy clay and sandy loam soils. Clay had a higher change in water retention then sandy clay and lastly sandy loam. Plant available water content (PAW) in all soils increased. In clay soil it increased with increase in SAP from 0.3291 at zero SAP to 0.6223 at 0.5% SAP. Sandy clay soil increased in PAW from 0.2721 at zero SAP to 0.5335 at 0.5% SAP and Sandy loam soils from 0.1691 at zero SAP to 0.3461 at 0.5% SAP. Hence, from the study SAP can be used to conserve irrigation water in the plant roots and therefore reducing the cost since PAW has been increased.

采用土壤孔隙表面分形维数预测土壤水分特征曲线

采用土壤颗粒体积累积曲线按照不同的粒径分级方法计算表面分形维数,避免了原始计算过程中颗粒密度不变的假设,改进了计算中的缺陷。结合土壤水分特征曲线分形模型—de Gennes模型,预测试样的SWRC。结果发现:不同颗粒分级只会影响表面分形维数的大小;相同颗粒分级情况下,计算得出的分形维数随着土壤粘粒含量降低而减小;采用D2(最大半径为1mm)的分级情况计算出的表面分形维数,预测得出的结果与实测值相差偏大,RMSE≥2.11E-02cm3/cm3只适合粗略估计田间土壤的水分特征曲线;通过D1(最大半径为0.1mm)计算出的表面分形维数,结合de Gennes模型预测水分特征曲线结果与实测值非常接近,RMSE≤0.0105cm3/cm3。研究表明采用土壤颗粒体积累积曲线计算表面分形维数,并预测土壤水分特征曲线是合理的,具有较高的预测精度。

Soil-water characteristics of Gaomiaozi bentonite by vapour equilibrium technique

Soil-water characteristics of Gaomiaozi(GMZ)Ca-bentonite at high suctions(3–287MPa)are measured by vapour equilibrium technique.The soil-water retention curve(SWRC)of samples with the same initial compaction states is obtained in drying and wetting process.At high suctions,the hysteresis behaviour is not obvious in relationship between water content and suction,while the opposite holds between degree of saturation and suction.The suction variation can change its water retention behaviour and void ratio.Moreover,changes of void ratio can bring about changes in degree of saturation.Therefore,the total change in degree of saturation includes changes caused by suction and that by void ratio.In the space of degree of saturation and suction,the SWRC at constant void ratio shifts to the direction of higher suctions with decreasing void ratio.However,the relationship between water content and suction is less affected by changes of void ratio.The degree of saturation decreases approximately linearly with increasing void ratio at a constant suction.Moreover,the slope of the line decreases with increasing suction and they show an approximately linear relationship in semi-logarithmical scale.From this linear relationship,the variation of degree of saturation caused by the change in void ratio can be obtained.Correspondingly,SWRC at a constant void ratio can be determined from SWRC at different void ratios.

电阻率法确定土壤水分特征曲线初探

以取自青岛市郊区的田间土样为研究对象,通过自制的室内土壤电阻率测量装置,测定了土壤的电阻率及对应的含水量,建立了电阻率-含水量关系模型。基于Ku/pF非饱和导水率测量系统测定的土壤水分特征曲线,借助含水量这一中间量,推求出了土壤电阻率-基质吸力关系模型,从而可以根据电阻率计算出对应的土壤基质吸力。耦合土壤电阻率-含水量关系模型与土壤电阻率-基质吸力关系模型,达到了预测土壤水分特征曲线的目的,为电阻率法在区域尺度空间和时间上预测土壤水分特征曲线提供了新的途径。

考虑孔隙水微观赋存形态的非饱和粉土有效应力方程及其验证

有效应力参数的合理确定是非饱和土有效应力研究的重要内容。然而,现有的有效应力参数未能较好地考虑孔隙水的微观赋存形态对有效应力的影响。为此,分析了孔隙水的微观赋存形态,明确了孔隙水可分为收缩膜、吸附水和毛细水,建立了非饱和粉土的扩展三相孔隙介质模型,即孔隙气、毛细水和广义土骨架。基于该模型,采用分相平衡分析法,推导了非饱和粉土的有效应力方程,该方程通过采用毛细水有效饱和度合理地考虑了毛细水对有效应力的影响。依据推导的有效应力方程,提出了非饱和粉土的抗剪强度公式。采用5种不同围压下重塑非饱和粉质黏土试验数据验证了提出的公式。结果表明:与现有的抗剪强度公式相比,本次提出的公式更好地预测了重塑非饱和粉质黏土的抗剪强度随基质吸力的变化规律。因此,运用提出的抗剪强度公式评价非饱和土边坡稳定性、地基承载力和挡土墙稳定性将会取得更好的效果。

一种改进的土壤水分特征曲线模型及其验证

土壤水分特征曲线是土壤水分与溶质运移模型必需的输入参数。本文在传统的van Genuchten模型和Campbell模型的基础上,提出了一种基于自适应权重的土壤水分特征曲线改进模型。验证发现,改进模型适用性更强,且能获得更好的模拟效果。特别是,改进模型为一个连续可微函数,能够满足非饱和土壤水流Richards方程数值求解的前提,因而具有较大的推广应用潜力。

Shear strength of an unsaturated weakly expansive soil

To study the weakly expansive clay obtained from a slope along Wuhan—Shiyan expressway in Hubei Province,soil-water property tests and some unsaturated triaxial tests with suction control were conducted,and the soil-water retention curve（SWRC） and unsaturated shear strength of this soil were obtained.Results show that the air-entry suction and the residual degree of saturation of the tested soil are 106 kPa and 8%,respectively.The boundary effect zone and the transition zone can be identified on the desorption curve,but the residual zone is not so obvious.The unsaturated shear strength increases as suction increases within the range of controlled suction in the test,and friction angle,b,in the triaxial shear test is 17.6°.Based on the results,constitutive models for predicting the unsaturated shear strength using the SWRC were evaluated,and comparisons between prediction and measurement were made.It is concluded that for engineering purpose,the constitutive model should be carefully selected based on soil properties when predicting the unsaturated shear strength using the SWRC.

Determining the soil-water retention curve using mercury intrusion porosimetry test in consideration of soil volume change

It is well-known that a close link exists between soil-water retention curve(SWRC)and pore size distribution(PSD).Theoretically,mercury intrusion porosimetry(MIP)test simulates a soil drying path and the test results can be used to deduce the SWRC(termed SWRCMIP).However,SWRCMIP does not include the effect of volume change,compared with the conventional SWRC that is directly determined by suction measurement or suction control techniques.For deformable soils,there is a significant difference between conventional SWRC and SWRCMIP.In this study,drying test was carried out on a reconstituted silty soil,and the volume change,suction,and PSD were measured on samples with different water contents.The change in the deduced SWRCMIP and its relationship with the conventional SWRC were analyzed.The results showed that the volume change of soil is the main reason accounting for the difference between conventional SWRC and SWRCMIP.Based on the test results,a transformation model was then proposed for conventional SWRC and SWRCMIP,for which the soil state with no volume change is taken as a reference.Comparison between the experimental and predicted SWRCs showed that the proposed model can well consider the influence of soil volume change on its water retention property.

Incorporation of a nanotechnology-based additive in cementitious products for clay stabilisation

The mechanical performances and water retention characteristics of clays,stabilised by partial substitution of cement with by-products and inclusion of a nanotechnology-based additive called RoadCem(RC),are studied in this research.The unconfined compression tests and one-dimensional oedometer swelling were performed after 7 d of curing to understand the influence of addition of 1%of RC material in the stabilised soils with the cement partially replaced by 49%,59%and 69%of ground granulated blast furnace slag(GBBS)or pulverised fuel ash(PFA).The moisture retention capacity of the stabilised clays was also explored using the soil-water retention curve(SWRC)from the measured suctions.Results confirmed an obvious effect of the use of RC with the obtained strength and swell properties of the stabilised clays suitable for road application at 50%replacement of cement.This outcome is associated with the in-depth and penetrating hydration of the cementitious materials by the RC and water which results in the production of needle-like matrix with interlocking filaments e a phenomenon referred to as the‘wrapping’effect.On the other hand,the SWRC used to describe the water holding capacity and corresponding swell mechanism of clays stabilised by a proportion of RC showed a satisfactory response.The moisture retention of the RC-modified clays was initially higher but reduced subsequently as the saturation level increased with decreasing suction.This phenomenon confirmed that clays stabilised by including the RC are water-proof in nature,thus ensuring reduced porosity and suction even at reduced water content.Overall,the stabilised clays with the combination of cement,GGBS and RC showed a better performance compared to those with the PFA included.

Experimental Set-up for Determining Soil Water Retention Curves for Granular Soils During Drying

Soil water retention curves（SWRCs） provide an important means of describing the response of unsaturated soils during drying / wetting processes in terms of variations of degree of saturation, water content or void ratio with suction. A key consideration in generating these curves is how to measure the suction. Frequently the filter paper technique is adopted, especially when high suctions are developed, e.g. with plastic clays. As each measurement takes at least a week with this technique, it can take months or years to generate a full SWRC in drying and wetting. Developments in laboratory tensiometers now allow matrix suctions up to about 1.5 MPa to be measured. With such a device it is possible to develop SWRCs for granular soils such as silts and clays in hours or days by continuous measurement. This paper describes an experimental set-up that was developed to measure changes in volume, water content and matrix suction during drying of three granular soils. Limitations of the apparatus and usefulness of the curves are discussed.

On the thermo-mechanical properties of unsaturated soils

The establishment of energy balance equation is necessary to study the thermo-mechanical properties of unsaturated soils.To solve this equation,the determination of two fundamental parameters as volumetric specific parameter and thermal conductivity coefficient is essential.In this paper,the effective thermal conductivity coefficient of dry soil grain is analyzed for soils with different compositions,and the thermo-mechanical properties of porous media with water and gas are studied by considering the soil water retention curve（SWRC）.Different methods,i.e.volumetric average method,self-consistent method,Hashin-Strikman method,are employed to calculate thermal conductivity coefficients,and a new method is proposed to determine the thermo-mechanical parameters.Comparison of the results obtained by different methods shows that the proposed method is in a good agreement with the experimental results and is suitable for describing the main properties of the thermo-mechanical behaviors of soils.The relationship between the SWRC and the seepage curve is further studied by the natural proportional rule.The characteristics of the SWRC,its differential coefficient and the seepage curve,are investigated by considering the physico-mechanical mechanism;the limit scopes of the indices of the SWRC and the seepage curve are also given.

粘性土水土特征曲线的试验研究

水土特征曲线(SWRC)描述了非饱和土含水量和基质势能间的本构关系,是工程地基勘察的重要参考依据。本文选取10种不同种类的天然粘性土壤,通过Lu(2016)模型对试验测得的吸力和实际含水率进行拟合,理解分析粘土SWRC的特征,给出基于土壤持水机理的SWRC区域划分范围。最后根据本文拟合图线形状的分析和现有文献资料的总结,得出SWRC本质和基础的影响因素是矿物成分和孔隙结构的结论。

Determination of strain-dependent soil water retention characteristics from gradation curve

The importance of soil water retention characteristics in modelling the hydro-mechanical response of unsaturated soils has been well recognised by many investigators in recent years.Determination of strain-dependent soil water retention curve(SWRC)is likely to be extraordinarily difficult.The first two authors have recently shown that SWRC can be computed from the gradation curve and the calculation result is consistent with the experimental results obtained from pressure plate tests.In this paper,based on a hypothesis related to change in the pore size distribution(POSD)due to volumetric strain of soil skeleton,a method to compute strain-dependent SWRC is presented.It is found that at initial degrees of saturation higher than 0.8,the influence of volumetric strain may be marginal whilst at initial degrees of saturation lower than 0.8,its influence is likely to be substantial.In all cases,the gradation curve of the soil affects the SWRC.

基于SFG模型的非饱和沉积土本构模型

为使修正后的模型能够更好地反映非饱和沉积土的持水和力学性质,对SFG (ShengFredlund-Gens)模型进行修正.用平均骨架应力代替净应力作应力状态变量,考虑饱和度对非饱和土变形的影响.通过分析泥浆固结土(沉积土)在等吸力条件下等向压缩和三轴压缩试验数据,得出饱和度和孔隙比的关系,并把变形考虑到持水曲线模型中.由修正后的体变方程以及持水曲线方程推导出加载湿陷屈服面方程,在修正剑桥模型基础上推导出三轴应力状态下的本构方程,并采用能统一描述剪缩剪胀性的硬化参数.基于同一模型参数,模型可以统一预测吸力控制下各向等压和三轴剪切路径下非饱和沉积土的持水和力学特性.

温度影响下压实红粘土持水特性研究

通过渗析法和水汽平衡法研究不同温度控制下干密度1.7 g/cm^3压实红粘土持水特性(SWRC:soil water retention characteristics)。试验结果表明:20℃下干密度1.7 g/cm^3压实红粘土进气值约为110 k Pa;试样控制的温度越高,压实红粘土样持水能力越低,土样进气值随着温度升高而减小,且呈线性关系;Van Genuchten(1980年)土水特征模型能很好的描述干密度1.7 g/cm^3压实红粘土持水特性曲线。

The Roles Played by the Staff and Workers' Representative Congress in the Formation of Work Regulations

Article 4 of the Labor Contract Law lays down the right of the Staff and Workers＇ Representative Congress （SWRC） to deliberate on the formulation of （intra-enterprise） work regulations, but this has become a ＂soft＂ law in judicial practice. The judicial criteria for judging the validity of work regulations are in essence determined by the judge＇s judgment on their reasonableness. As an important embodiment of Chinese politics, economics and culture, the transformation of the SWRC that accompanied the market economy has not negated its value as an indigenous traditional resource. The SWRC does not just enjoy deliberative rights in the formation of regulations, as clearly specified in constitutional law, but also has rights under the law in local legislation and practice. Hence the system of work regulations is neither a unilateral decision on the part of management nor a contract, but rather an autonomous norm developed through the SWRC mechanism. Given the mandatory nature of Article 4 of the Labor Contract Law, regulations will only be valid after they havegone through a democratic process. The further development of the theory of normative system formation should endow the SWRC with greater rights and integrate it smoothly with the collective contract system to standardize collective labor relations.

Effect of biochar type on infiltration,water retention and desiccation crack potential of a silty sand

Biochar is a carbon-rich material obtained after thermochemical conversion of biomass under no oxygen environment.The effect of biochar amendment on soil properties,such as water retention,infiltration and desiccation crack potential was studied in the recent years.However,the effect of biochar or feedstock type on these properties is not explicit.This study investigates the effect of two different(in terms of feedstock)types of biochar on the water retention,infiltration and desiccation crack-ing behavior of compacted silty sand.Water retention characteristics,infiltration rate and the progression of desiccation cracks were measured after compacting soil amended with 5-10%(w/w)biochar produced from water hyacinth(WHB)and mesquite.Measurements were also taken for an unpyrolyzed material coir pith(CP,sourced from coconut husk)-amended soil for comparing the results of biochar-amended soil.The results show that the amendment of 5%to 10%biochar increased the maximum water holding capacity(θs),air entry value(AEV)and water content at 1500 kPa(θ1500)of the soil,whereas decreased the infiltration rate and peak crack intensity factor(CIF)of the soil.Moreover,the application of CP increased the infiltration rate.The amendment of WHB showed the highest increment in AEV andθ1500 and the highest decrement in infiltration rate and CIF compared to the other amendments.Based on the results,it is advisable to use the WHB-amended soil in bioengineered structures that could promote the growth of vegetation by higher water retention and could reduce the potential of leachate formation by decreasing water infiltration and desiccation crack potential.

利用混合改进的遗传算法反演F-X模型参数

构建混合改进的遗传算法(GA),实现F-X模型参数反演,以期为非饱和渗流机制研究提供指导。以F-X模型中的系数a、m、n以及饱和体积含水量θ_(s)作为模型参数,以简单十进制遗传算法为基础,融入优体克隆操作等算子,形成混合改进的遗传算法;采用已有数据进行算法验证,对不同干密度土样的F-X模型参数进行反演,明确模型参数与干密度间的相关关系。研究发现:1)混合改进的遗传算法反演F-X模型参数精度较高,模型拟合结果与实测值均方差均小于0.03;2)随着土样干密度的增大,F-X模型的参数a是控制土—水特征曲线(SWRC)的主要因素,而参数m、n变化不显著;3)建立的F-X模型参数与干密度间的关系也可广泛适用于其他土样的SWRC,大大简化了模型参数的获取过程。