Influence of dry density on soil-water retention curve of unsaturated soils and its mechanism based on mercury intrusion porosimetry

The soil-water retention curve(SWRC)can be used to evaluate the ability of unsaturated soils to attract water at various water contents and suctions. In this study, drying SWRCs for a kind of sandy soil were obtained in the laboratory by using self-modified SWRC apparatus. In addition, the porosity and the pore size distribution of the samples were investigated by a mercury porosimetry test in order to analyze the effect of dry density. Results showed that the soil-water retention of the soil specimens was strongly dependent on the dry density. Under zero suction, soil specimens with a higher dry density exhibited lower initial volumetric water content. The higher the dry density of soil, the more slowly the volumetric water content decreased with the increase of suction. There was a general and consistent trend for a soil specimen to possess a larger air-entry value and residual suction, while smaller slope of SWRC when it had a higher density. This was probably attributed to the presence of smaller interconnected pores in the soil specimen with a higher dry density. The proportion of large diameter pores decreased in comparison to pores with small diameters in the soil tested. The measured total pore volume of the soil specimen, which had a larger dry density, was lower than that of the relatively loose specimens.     

A new equation for dielectric permittivity of saturated soils based on polarization mechanics

Based on polarization mechanisms, such as electronic, ionic and orientational polarizations, a new equation for dielectric permittivity of soil is proposed to interpret the dielectric behavior of a mixture like soil, in terms of polarization process of its components and the interactions between its components. The dielectric permittivity is expressed in terms of a fre- quency-dependent part and a frequency-independent part. These two parts correspond to polarizations occurred at different fre- quency range. It is a new volumetric mixing model with theoretical background. Based on time domain reflectometry （TDR） measurements of saturated soil samples and test data from literature, comparisons of this model with some well established mixing models show that the curves for saturated sand soils and slurries resulted from the new equation, which agree well with TDR measurements, are close to those calculated from Birchak＇s model.     

钱塘江吹填土的沉淀特性研究

钱塘江标准塘Ⅴ期的吹填土的颗粒分析曲线和沉淀试验显示：对粉土来讲，干密度、沉积的快慢与含水量没有明显关系；级配较好的土，沉积后的干密度较大；土的自重在欠固结土中发挥着重要作用。     

季节冻土冻融循环过程中水分迁移试验研究

文章对哈尔滨地区的粉质粘土进行了冻结过程的水分迁移试验,考察了含水率、冻结温度及干密度在封闭系统的条件下对粉质粘土中水分迁移的影响。结果表明,控制含水率和干密度相同,顶板的冻结温度越高,水分迁移量越大,顶板冻结温度为-3℃的水分迁移量较冻结温度为-9℃的水分迁移量大;控制顶板冻结温度和干密度相同,初始含水率大的试样,水分迁移量大;控制顶板冻结温度和含水率相同,水分迁移量随干密度的增加而减小。     

水泥砂浆固化土物理性质研究

通过室内试验系统地对水泥砂浆固化土的物理特性进行研究,分析水泥砂浆固化土的重度、渗透系数和水稳定性等物理特性随水泥掺入比、掺砂量、龄期等因素的变化规律。从几个基本物理性质上来看,采用水泥砂浆固化软土形成的加固区可同时满足自重、渗透性和水稳定性等几个方面的要求。     

Prediction of the P-leaching potential of arable soils in areas with high livestock densities

Due to long-term positive P-balances many surface soils in areas with high livestock density in Germany are oversupplied with available P, creating a potential for vertical P losses by leaching. In extensive studies to characterize the endangering of ground water to P pollution by chemical soil parameters it is shown that the available P content and the P concentration of the soil solution in the deeper soil layers, as indicators of the P-leaching potential, cannot be satisfactorily predicted from the available P content of the topsoils. The P equilibrium concentration in the soil solution directly above ground water table or the pipe drainage system highly depends on the relative saturation of the P-sorption capacity in this layer. A saturation index of 〈20% normally corresponds with P equilibrium concentrations of〈0.2 mg P/L. Phytoremediation may reduce the P leaching potential of P-enriched soils only over a very long period.     

生石灰与熟石灰改良泥质粉砂岩的对比分析

通过对生、熟石灰的改良土在不同掺灰量下进行无侧限抗压强度试验,探求不同掺灰量改良后土的强度关系,并通过其改良机理及反应方程,获取生、熟石灰改良效果差别的定量关系。结果表明：相同的掺灰量下,生石灰改良土的最大干密度、最佳含水量和无侧限抗压强度较熟石灰的改良土都要大：但生、熟石灰改良土最佳掺灰量所能达到的最大无侧限抗压强度相差无几。     

A simple model for the hysteretic elastic shear modulus of unsaturated soils

Considering the great importance of the elastic shear modulus G₀ of unsaturated soils to the serviceability of many geo-structures in geo-energy and geo-environmental engineering, some semi-empirical models have been reported for the G₀ of unsaturated soils. Existing models require at least three parameters and the calibration of the model parameters requires extensive time-consuming unsaturated soil tests. In this study, a simple semi-empirical model is proposed for the hysteretic G₀ of unsaturated soils, requiring only two parameters. The constitutive variables of the mean Bishop’s stress and a bonding variable are adopted for considering the average stress between soil particles and the additional normal forces between soil particles provided by water menisci. The derived equation is applied to simulate the G₀ of unsaturated silts and sands. Comparisons between the measured and calculated results demonstrate that the proposed equation is able to describe the influences of various factors on G₀, including mean net stress, suction, wetting-drying, and void ratio.     

志丹县泥浆泵筑坝土料的物理力学性质研究

以陕西省志丹县顺宁镇任坪村保娃沟门流域的前拐沟黄土作为研究对象,按照土工试验规程（SL237-1999）进行分类、击实、渗透等各项试验,对试验结果进行分析。分析结果表明,该流域黄土的Cu〉5,Cc∈（1,3）,小于0.005mm的土粒含量18.95%,土料的液限ωL平均为27.98%,塑限WP平均为17.10%,塑性指数Ip平均为10.89;土样最大干密度为1.70g/cm^3,最优含水率为14.99%;渗透系数为4.32×10^-5cm/s。该区土壤粒径分布不均匀且级配良好,渗透性较好,适合筑坝工程要求。     

水流量实验装置计算机控制系统

该设计是开发出水流量标准装置的计算机控制系统,涵盖了流体力学、检测技术、误差理论、电工电子以及Visual basic 6.0语言等方面的知识,设计内容包括：实验装置精确度检定,用标准表法或称重法标定涡轮流量计和浮子流量计,实验数据的保存和查询,报表的打印输出.     

开封城市土壤主要性质及空间分布分析

采用正方形网格法在开封市布设土壤样点137个,采集表层（0 ～ 10 cm）土壤样品进行城市土壤性质的分析.研究发现：城市土壤密度、pH、有机质和全氮均与郊区存在差异,且表现出较大的空间异质性.开封市土壤密度的功能区差异为休闲区＞道路临近区＞居民区＞文教区＞行政区＞工业区,水平分布表现为由西北向东南降低;土壤的pH呈强碱性,空间分布表现为自东南向西北增大;土壤有机质含量为工业区＞行政区＞道路临近区＞居民区＞文教区＞休闲区,由东至西呈环状递减;全氮含量为工业区＞行政区＞道路临近区＞居民区＞文教区＞休闲区,由城市东南区域向西北区域降低.     

盐渍土水分下渗能力及水盐动态运移试验

为探究盐渍化土壤水分下渗规律、水分下渗能力及水盐动态运移过程,设计了土壤剖面分层定水头供水及土壤剖面变水头供水下渗实验。测定不同层位土壤水分下渗率、含水率、孔隙水溶液电导率及土壤体电导率等参数,进行入渗条件下水盐动态运移规律分析。试验结果表明:盐渍化土水分下渗规律可由积水入渗Kostiakov模型进行刻画;浅层0~40 cm土壤相对于深层40~60 cm土壤具有较强的拦截和贮存入渗水分能力;盐渍化土壤盐分变动带位于浅层0~40 cm,且20~40 cm深度的土壤盐分波动幅度较大,深层40~60 cm土壤孔隙水溶液盐分向下运移的通量与土壤体盐分对其的补充量达到动态平衡,水分下渗过程中深层土壤孔隙水盐分含量相对平稳。实验结果为盐渍土的防治提供参考。     

Q235钢在不同湿度的青海盐湖盐渍土壤中的腐蚀行为

利用极化曲线技术、电化学阻抗测试技术、扫描电镜和表面能谱等方法．研究了Q235钢在不同湿度的两种青海盐湖边盐渍土壤中的腐蚀行为．试验结果表明，湿度对Q235钢腐蚀的影响显著．随着土壤湿度的增加，Q235钢在盐湖盐渍土壤中的腐蚀速率也增加，当含水量增大到10％～15％时．腐蚀速率达到最大，然后腐蚀速率随着湿度增加而减小；Q235钢在这两种盐渍土壤中，在同一湿度时，盐含量高的土壤腐蚀较快．     

A Specification Error Test That Uses Instrumental Variables to Detect Latent Quadratic and Latent Interaction Effects

The relations between the latent variables in structural equation models are typically assumed to be linear in form. This article aims to explain how a specification error test using instrumental variables (IVs) can be employed to detect unmodeled interactions between latent variables or quadratic effects of latent variables. An empirical example is presented, and the results of a simulation study are reported to evaluate the sensitivity and specificity of the test and compare it with the commonly employed chi-square model test. The results show that the proposed test can identify most unmodeled latent interactions or latent quadratic effects in moderate to large samples. Furthermore, its power is higher when the number of indicators used to define the latent variables is large. Altogether, this article shows how the IV-based test can be applied to structural equation models and that it is a valuable tool for researchers using structural equation models.     

Mean and Mean-and-Variance Corrections With Big Data

Mean and mean-and-variance corrections are the 2 major principles to develop test statistics with violation of conditions. In structural equation modeling (SEM), mean-rescaled and mean-and-variance-adjusted test statistics have been recommended under different contexts. However, recent studies indicated that their Type I error rates vary from 0% to 100% as the number of variables p increases. Can we still trust the 2 principles and what alternative rules can be used to develop test statistics for SEM with “big data”? This article addresses the issues by a large-scale Monte Carlo study. Results indicate that empirical means and standard deviations of each statistic can differ from their expected values many times in standardized units when p is large. Thus, the problems in Type I error control with the 2 statistics are because they do not possess the properties to which they are entitled, not because of the wrongdoing of the mean and mean-and-variance corrections. However, the 2 principles need to be implemented using small sample methodology instead of asymptotics. Results also indicate that distributions other than chi-square might better describe the behavior of test statistics in SEM with big data.     

低剂量石灰土的压实度控制

结合S327一级公路路基施工实例,针对工程中石灰土压实度差异较大的问题,采用EDTA滴定法,对不同石灰等级的不同剂量石灰土进行不同龄期有效钙镁含量测试,并对5%石灰剂量的拌和石灰土进行了不同龄期灰剂量试验,分析了石灰土压实度的影响因素。试验表明,现场使用的石灰必须与标准曲线的相对应,并应考虑石灰和石灰土中的有效钙镁含量随存放时间的衰减,以正确反映石灰的真实剂量而取用合理的干密度,从而实现压实度的有效控制。     

Effects of ammonium application rate on uptake of soil adsorbed amino acids by rice

In recent years, excessive use of chemical nitrogen (N) fertilizers has resulted in the accumulation of excess ammonium (NH ₄ ⁺ ) in many agricultural soils. Though rice is known as an NH ₄ ⁺ -tolerant species and can directly absorb soil intact amino acids, we still know considerably less about the role of high exogenous NH ₄ ⁺ content on rice uptake of soil amino acids. This experiment examined the effects of the exogenous NH ₄ ⁺ concentration on rice uptake of soil adsorbed glycine in two different soils under sterile culture. Our data showed that the sorption capacity of glycine was closely related to soils;’ physical and chemical properties, such as organic matter and cation exchange capacity. Rice biomass was significantly inhibited by the exogenous NH ₄ ⁺ content at different glycine adsorption concentrations. A three-way analysis of variance demonstrated that rice glycine uptake and glycine nutritional contribution were not related to its sorption capacity, but significantly related to its glycine:NH ₄ ⁺ concentration ratio. After 21-d sterile cultivation, the rice uptake of adsorbed glycine accounted for 8.8%;–22.6% of rice total N uptake, which indicates that soil adsorbed amino acids theoretically can serve as an important N source for plant growth in spite of a high NH ₄ ⁺ application rate. However, further studies are needed to investigate the extent to which this bioavailability is realized in the field using the ¹³C, ¹⁵N double labeling technology.     

用^137Cs衰减法测定土壤密度和含水量的蒙特卡罗模拟

运用γ射线衰减法,通过蒙特卡罗模拟标定了水和干土的质量衰减系数,在此基础上,通过设计容器测定了土壤的密度和含水率．模拟结果和实际符合的很好,从而验证了此方法的可行性．     

封闭系统正冻土水流的一个计算模型

A computational model of water migration flux of fine porous soil in frost heave was investigated in a closed system. The model was established with the heat-mass conservation law and from some previous experimental results. Through defining an auxiliary function an empirical function in the water migration flux, which is difficult to get, was replaced. The data needed are about the water content along the soft colunm after test with enough long time. We adopt the test data of sample soil colunms in [1] to verify the model. The result shows it can reflect the real situation on the whole.     

Parameter Recovery in the Graded Response Model Using MULTILOG

The graded response model can be used to describe test-taking behavior when item responses are classified into ordered categories. In this study, parameter recovery in the graded response model was investigated using the MULTILOG computer program under default conditions. Based on items having five response categories, 36 simulated data sets were generated that varied on true θ distribution, true item discrimination distribution, and calibration sample size. The findings suggest, first, the correlations between the true and estimated parameters were consistently greater than 0.85 with sample sizes of at least 500. Second, the root mean square error differences between true and estimated parameters were comparable with results from binary data parameter recovery studies. Of special note was the finding that the calibration sample size had little influence on the recovery of the true ability parameter but did influence item-parameter recovery. Therefore, it appeared that item-parameter estimation error, due to small calibration samples, did not result in poor person-parameter estimation. It was concluded that at least 500 examinees are needed to achieve an adequate calibration under the graded model.