Design and verification of an improved experimental platform for stray current in urban rail transit

With the rapid development of urban rail transit,there have been an urgent problem of excessive stray current.Because the stray current distribution is random and difficult to verify in the field,we designed an improved stray current experimental platform by replacing the simulated aqueous solution with a real soil environment and by calculating the transition resistance by measuring the soil resistivity,which makes up for the defects in the previous references.Firstly,the mathematical models of rail-drainage net and rail-drainage netground were established,and the analytical expressions of current and voltage of rail,drainage net and other structures were derived.In addition,the simulation model was built,and the mathematical analysis results were compared with the simulation results.Secondly,the accuracy of the improved stray current experimental platform was verified by comparing the measured and simulation results.Finally,based on the experimental results,the influence factors of stray current were analyzed.The relevant conclusions provide experimental data and theoretical reference for the study of stray current in urban rail transit.

Simulation and Analysis of Land System Structure Changes in Huang-Huai-Hai Plain Area

The dynamic changes of land system in Huang - Huai - Hai Plain between 1988 and 2000 were researched in this paper. Spatial dominance econometric model was estabilished on 1 km cell to quantificafionally analyze the driving-force for the dynamic change mechanism of land system, such as natural, social and economic factors. The future dynamic changes of land system in Huang - Huai - Hai Plain on each 1 km cell during 2000 to 2020 were stimulated by combining the dynamic changes of land system on each 1 km cell with different situations. The research indicated that the dynamic changes of land system structure changed mainly from the cultivated areas to building areas and industrial areas, and forest areas increased during this period. Although the revolutions of land system structure were different during 2000 to 2020 with the different referrence standard, ecological protection and economic development, the primary dynamic changes of land system structure were that the increase of building land areas with the decline cuhivaled land areas and the increase of woodlands.

糖料蔗全程机械化的关键技术及发展建议

通过对实现全程机械化的关键技术,即种植规划、土地整理、联合种植、高效全程机械化管理、高效机械收割、宿根蔗管理全过程及工序进行的分析总结,以及分析当前影响全程机械化技术应用的主要原因。为实现高效率、高质量的机械化作业及甘蔗的可持续发展提供意见和建议。

Soil Carbon Balance in a Native Temperate Grassland in the Xilin River Basin of Inner Mongolia

Based on historical data and field investigation, some major fluxes and reserves of carbon were estimated, and a tentative analysis of the soil carbon balance was made in a native grassland community in the Xilin River basin of Inner Mongolia. Major results were reported as follows: 1) Annual average carbon input from above-ground biomass production was 79.8 g C(.)m(-2.)a(-1), and from root biomass to 30 cm. depth averaged 311.9 g C(.)m(-2.)a(-1). The summed mean annual carbon input of shoot and root materials in the study site was approximately 391.7 g C(.)m(-2.)a(-1). 2) The annual amount of above-ground biomass consumed by insects averaged 14.7 g C(.)m(-2.)a(-1), and the carbon output by leaching or light-chemical oxidation was 3.2 g C(.)m(-2.)a(-1) The annual evolution rate of CO2 from net soil respiration averaged 346.9 g C(.)m(-2.)a(-1), and the summed mean annual output was approximately 364.8 g C(.)m(-2.)a(-1). 3) A mature, steady-state system could be assumed for the community for which growth and decay were approximately in balance, with a net carbon accumulation of about 26.9 g C(.)m(-2.)a(-1). Based on the soil organic carbon density of the field, the turnover Irate of soil carbon in 0 - 30 cm depth was calculated to be 6.2%, with a turnover time of 16 years.

The Estimation of Cultivated Land Threshold Value in Hotan Oasis

[Objective] Water shortage is a key natural factor limiting arid economic development and ecological security.However,the large-scale land reclamation against natural laws has been speeding up water consumption,and the ecological water use which is the primary condition for maintaining ecological security was squeezed.Moreover,the fragile oasis ecosystem would be destroyed dramatically.In order to maintain ecological security,it is urgent to evaluate the threshold value of cultivated land.[Method] The method of water-soil balance was used to evaluate the threshold value of cultivated-land on the premise of allocating downstream ecological water demand.[Result] Under the frequency of 75%（P =75 for short） in Hotan River,the threshold value of cultivated-land in Hotan Oasis would be 13.83×10^4,16.78×10^4and 16.50×10^4hm^2in 2010,2020 and 2030 respectively.Under the frequency of 50%（P=50 for short）,the threshold value of cultivated land in Hotan Oasis would be 14.95 ×10^4,18.08 ×10^4and 17.78 ×10^4hm^2in 2010,2020 and 2030 respectively.If effective measures are not taken to control cultivated-land expansion,the cultivated land area will be 2.78×10^4and 5.07×10^4hm^2more than the threshold values of cultivated land at P =75 in 2020 and 2030 respectively.Even if the efficient water-saving technique are adopted,the water requirement of crop use will increase from 19.77×108to 20.82×108and 21.95×108m3during 2010-2030,and then the ecological water use cannot be guaranteed.[Conclusion] The cultivated-land expansion would threaten the ecological security in Hotan River and Tarim River.Therefore,some strict measures should be taken to protect desert-oasis ecotone,an important constituent of oasis ecosystem which has vital role in maintaining the stability of oasis,and to prohibit cultivated-land expansion.

Distribution of Nutrients in Arable Land Soil of Western Hainan

[Objective] This study aimed to reveal distribution characteristics of soil nutrients in tropical farmland, thereby providing a reference for cropland management and balanced fertilization in the tropical area. [Method] Combining field survey and laboratory analysis, distribution status of nutrients in arable land of Baisha Li Autonomous County of Hainan Province was investigated. [Result] The soil in Baisha Li Autonomous County was acidic in overall with average pH value of 5.0. it had medium organic matter level （average of 19.3 g/kg） and rich alkali-hydrolyzable nitrogen content, but was lack of available phosphorus and available potassium. The spatial distribution of available nitrogen, available phosphorus and available potassi- um in the soil was uneven. The spatial distribution of soil nutrients was mainly related to soil parent materials of the investigated area and pH value of the investigated soil. [Conclusion] According to the distribution characteristics of nutrients in the soil, awareness of land use and land maintenance should be strengthened, application amount of organic fertilizers should be increased, chemical fertilizers should be applied rationally, and fertilization structure should be optimized in the future.

水泥地坪起砂的原因及防治

水泥楼、地面,操作简单,造价便宜,所以长期以来在一般住宅、车间、仓库等工程上广泛采用。但由于设计、材料、操作,养护、使用等问题,使有些工程出现局部或大面积起砂,地面强度、抗磨能力均遭不同程度的损伤,从而影响使用功能及工程质量等级核定。 1 现状 根据受监单位工程的统计和有关施工企业提供的数据,水泥地坪起砂,在各个施工企业所承担施工的具体工程上,其发生率各不相同,其幅度约为7.8—20.6％,同时水泥地坪起砂现象,在随捣随光的面层,或水泥砂浆面层均有不同程度的发生,现浇砼上加水泥砂浆面层的起砂发生率略高于砼随捣随光的面层,高出幅度为12—38％。

Effect of Freezing and Thawing on Ammonium Adsorption in Dryland Soil

[Objective] This study aimed to investigate the effect of freezing and thawing on ammonium adsorption in dryland soil. [Method] The lab simulation test was conducted to study the effect of freeze-thaw action on the total adsorbed amount of ammonium （deionized water extract） and strongly-adsorbed amount of ammonium （0.01 mol/L KCl solution extract） in the dryland soil of Sanjiang Plain. [Result] Compared with linear equation, Freundlich equation could better fit the total adsorbed amount of ammonium in dryland soil （R 2 0.99, SE1.69）. The freeze-thaw action almost had no influence on the total adsorbed amount of ammonium. When the initial concentration of NH 4 ＋ increased from 0 to 200 mg/L, the total adsorbed NH 4 ＋ amount increased from -0.52 to 39.0 mg/kg under freeze-thaw treatment （FTT）, while it increased from -0.70 to 38.5 mg/kg under unfreeze-thaw treatment （UFTT）. However, the strongly-adsorbed amount of ammonium presented linear relationship with the concentration of NH 4 ＋ （R 2 0.99, SE0.54）, and the strongly-adsorbed amount of ammonium increased significantly by FTT. When the initial concentration of NH 4 ＋ increased from 0 to 200 mg/L, the strongly adsorbed amount increased linearly from 2.36 to 28.81 mg/kg for FTT and from -4.25 to 25.12 mg/kg for UFTT. The freezethaw action decreases the concentration of NH 4 ＋ in soil solution when the net strongly-adsorbed NH 4 ＋ in soil is zero., therefore, FTT helped to reduce the leaching of ammonium ions in soil. Freeze-thaw action mainly influenced the exchangeable adsorbed NH 4 ＋ in soil. [Conclusion] This study provides theoretical basis for preventing excessive soil nitrogen from entering into water body and controlling water entrophication.

Equilibrium of Organic Matter in Heavy Fraction for Three Long-term Experimental Field Soils in China

Considerable evidence that the soil organic matter （OM） level in agricultural soils will gradually over time reach an equilibrium state under certain bioclimatic conditions and for certain cropping systems has been accumulating. Although models or long-term experiments have been used, this research used physical fractionation procedure to attain an soil OM equilibrium value. To obtain soil OM equilibrium values in the heavy fraction, typical soils from three long-term field experiments at Fengqiu and Yingtan State Key Agro-Ecological Experimental Stations in China were studied using a simple density fractionation procedure and employing the Langmuir equation. Results for the fluvo-aquic soil with organic fertilizer treatments indicated that the soil OM equilibrium value in the heavy fraction was twofold more than that in the inorganic treatments; however, for the paddy soil developed on red soil the OM equilibrium value in the heavy fraction for both treatments was almost identical. It suggested that for fiuvo-aquic soils the increased potential of OM for the heavy fraction in the long run was larger for the organic than the inorganic fertilizer applications, whereas for paddy soils developed on red soils under the same conditions the present OM content in the heavy fraction was at or close to this equilibrium level for all treatments, and increased potential was very limited.

Forecast and Analysis of Soil Moisture Based on SIMPEL Model

The forecast of soil moisture lays foundation for water management in farmlands. The change of soil moisture is influenced by multiple meteorological fac- tors. It becomes much significant for improvement of agricultural production and ef- fective use of water to explore the rule of water dynamic at small scale, spatially or temporally. In the research, water dynamic in soil horizons at 0-40 cm in winter wheat belts was simulated by SIMPLE model as per water balance principle. Fur- thermore, ETp in fields was computed according to Haude method （DVWK stan- dards）; retained amount of water in fields and wilting coefficient were calculated based on soil parameters with SPAW （Soil-Plant-Air-Water）. The simulated results of SIMPLE model showed that the correlation of measured and simulated water con- tent in soils was 0.95 and relative error averaged lower than 3.1%, suggesting that the model would make a more precise estimation of water content in root zone in the area.

Effects of freeze-thaw cycles on fracture behavior of epoxy asphalt concrete

According to the winter temperature of Peking,the freeze-thaw（FT） condition in laboratory was determined.Seven groups of epoxy asphalt concrete（EAC） specimen were exposed to different FT cycles.The flexural modulus and fracture energy（G_F） of EAC exposed to different FT cycles were obtained through the 3-point bending test.Meanwhile,the plane strain fracture toughness（K_（IC）） of EAC was obtained through numerical simulation.The results show that the flexural modulus of the FT conditioned EAC samples decreases with the increase of FT cycles.The FT damage of flexural modulus is 60%after 30 FT cycles.Nevertheless,with the increase of FT cycles,the G_F and K_（IC） of EAC decrease first and then increase after 15 FT cycles.

Estimation of Turnover and Equilibrium of Soil Organic Matter Using a Mathematical Approach

The methods based on N uptake of aerial-plants, soil organic matter (SOM) dynamics, Jenny's equation, and actual measurement of long-term field experiments in Jiaxing, Quzhou, Huangyan and Hangzhou of Zhejiang Province, China were used to determine the organic mineralization rate being helpful in estimating the organic requirement for SOM equilibrium. The results showed that the estimated mineralization ratios of SOM for Jiaxing and Quzhou were, respectively, 0.0404 and 0.0508 based on N uptake of aerial-plants in non-fertilized plots; 0.0405 and 0.012 using SOM dynamics in non-fertilized plots; and 0.0413 and 0.0513 using the actual investigated data and Jenny's equation. With Jenny's equation, soil organic C balance in manure + N-P-K plots was estimated at nearly 28.8 g kg-1 for Jiaxing and 32.4 g kg-1 for Quzhou with predicted SOM linearly related to the actual investigated values (r2 = 0.9640 for Jiaxing and 0.8541 for Quzhou). To maintain the SOM balance in the non-fertilized plots the recommended rate of organic materials was 3 000-6 600 kg ha-1, and the relevant rates of farm yard manure (FYM) in the manure and N-P-K plots were estimated at 3 375 (dry) and 17670 kg ha-1 (wet) for Jiaxing, 1845 (dry) and 6090 kg ha-1 (wet) for Quzhou.

Constitutive equations and finite element implementation of strain localization in sand deformation

A recently proposed model coupling with the solid-fluid of the saturated sand was utilized to study the deformation band. Based on the critical state plasticity model by Borja and Andrade, the hydraulic conductivity tensor was naturally treated as a function of the spatial discretization matrix about the displacement and the stress field, allowing a more realistic representation of the physical phenomenon. The fully Lagrangian form of the Darcy law was resolved by Piola algorithm, and then the flow law was gained, leading to the implementation of a modified model of the saturated sand. Then the criterion for the onset of localization was derived and utilized to detect instability. The constitutive model was implemented in a finite element program coded by FORTRAN, which was used to predict the formation and development of shear bands in plane strain compression of saturated sand. At last, the formation mechanism of the shear band was discussed. It is shown that the model works well, and the simulation sample bifurcates at 1.18% axial strain, which is in a good qualitative agreement with the experiment. The pore pressure greatly affects the onset and development of the deformation band, and it obviously increases around the localization-prone regions with the direction toward the outer side of the normal of the shear band, while the pore stress flows nearly horizontally and is distributed equally far away the shear band region.

Effect of Long-Term Fertilization on Organic Nitrogen Forms in a Calcareous Alluvial Soil on the North China Plain

In order to illustrate the change of nitrogen （N） supply capacity after long-term application of manure and chemical fertilizer, as well as to properly manage soil fertility through fertilizer application under the soil-climatic conditions of the North China Plain, organic N forms were quantified in the topsoil with different manure and chemical fertilizer treatments in a 15-year fertilizer experiment in a Chinese calcareous alluvial soil. Soil total N （TN） and various organic N forms were significantly influenced by long-term application of chemical fertilizer and manure. TN, total hydrolysable N, acid-lnsoluble N, amino acid N and ammonium N in the soil increased significantly （P 〈 0.05） with increasing manure and fertilizer N rates, but were not influenced by increasing P rates. Also, application of manure or N fertilizer or P fertilizer did not significantly influence either the quantity of amino sugar N or its proportion of TN. Application of manure significantly increased （P 〈 0.05） hydrolysable unknown N, but adding N or P did not. In addition, application of manure or N fertilizer or P fertilizer did not significantly influence the proportions of different soil organic N forms.

Global and Regional Surface Nitrogen Balances in Intensive Agricultural Production Systems for the Period 1970-2030

Global nitrogen (N) budgets for intensive agricultural systems were compiled for a 0.5 by 0.5 degree resolution. These budgets include N inputs (N fertilizer, animal manure, biological N fixation and atmospheric N deposition) and outputs (N removal from the field in harvested crops and grass and grass consumption by grazing animals, ammonia volatilization,denitrification and leaching). Data for the historical years 1970 and 1995 and a projection for 2030 were used to study changes in the recovery of N and the different loss terms for intensive agricultural systems. The results indicate that the overall system N recovery and fertilizer use efficiency slowly increased in the industrialized countries between 1970 and 1995, the values for developing countries have decreased in the same period. For the coming three decades our results indicate a rapid increase in both the industrialized and developing countries. High values of ＞ 80% for fertilizer use efficiency may be related to surface N balance deficits, implying a depletion of soil N and loss of soil fertility. The projected intensification in most developing countries will cause a gradual shift from deficits to surpluses in the coming decades.The projected fast growth of crop and livestock production, and intensification and associated increase in fertilizer inputs will cause a major increase in the surface N balance surplus in the coming three decades. This implies increasing losses of N compounds to air (ammonia, nitrous oxide and nitric oxide), and groundwater and surface water (nitrate).

Mechanized Tunneling in Soft Soils： Choice of Excavation Mode and Application of Soil-Conditioning Additives in Glacial Deposits

The history of the formation of the alpine region is affected by the activities of the glaciers, which have a strong influence on underground works in this area. Mechanized tunneling must adapt to the presence of sound and altered rock, as well as to inhomogeneous soil layers that range from permeable gravel to soft clay sediments along the same tunnel. This article focuses on past experiences with tunnel-boring machines （TBMs） in Switzerland, and specifically on the aspects of soil conditioning during a passage through inhomogeneous soft soils. Most tunnels in the past were drilled using the slurry mode （SM）, in which the application of different additives was mainly limited to difficult zones of high permeability and stoppages for tool change and modification. For drillings with the less common earth pressure balanced mode （EPBM）, continuous foam conditioning and the additional use of polymer and bentonite have proven to be successful. The use of conditioning additives led to new challenges during separation of the slurries （for SM） and disposal of the excavated soil （for EPBM）. If the disposal of chemically treated soft soil mate- rial from the earth pressure balanced （EPB） drive in a manner that is compliant with environmental legislation is considered early on in the design and evaluation of the excavation mode, the EPBM can be beneficial for tunnels bored in glacial deposits.

Discrete element simulation of mechanical characteristic of conditioned sands in earth pressure balance shield tunneling

The discrete element method (DEM) was used to simulate the flow characteristic and strength characteristic of the conditioned sands in the earth pressure balance (EPB) tunneling. In the laboratory the conditioned sands were reproduced and the slump test and the direct shear test of the conditioned sands were implemented. A DEM equivalent model that can simulate the macro mechanical characteristic of the conditioned sands was proposed,and the corresponding numerical models of the slump test and the shear test were established. By selecting proper DEM model parameters,the errors of the slump values between the simulation results and the test results are in the range of 10.3%-14.3%,and the error of the curves between the shear displacement and the shear stress calculated with the DEM simulation is 4.68%-16.5% compared with that of the laboratory direct shear test. This illustrates that the proposed DEM equivalent model can approximately simulate the mechanical characteristics of the conditioned sands,which provides the basis for further simulation of the interaction between the conditioned soil and the chamber pressure system of the EPB machine.

Quantitative Analysis of Relationships Between Crack Characteristics and Properties of Soda-saline Soils in Songnen Plain, China

The Songnen Plain has a typical soda-saline soil, which often shrinks and cracks under natural conditions during water evaporation. This study aims to analyze the relationships between the crack characteristics and the soil properties of soda-saline soils quantitatively, and attempts to establish prediction models for the main soil properties of soda-saline soils based on the results. In order to achieve these objectives, a desiccation cracking test was conducted using 17 soil specimens with different salinity levels under controlled laboratory conditions. Correlation analysis was then performed between the crack characteristics and the soil properties. The results indicate that the crack characteristics can well represent the surface appearances of cracked soils, they also can well distinguish the salinity levels of soda-saline soils while the clay contents and mineralogical compositions of soils are stable. Among the crack characteristics, crack length has the best relationships with the salinity levels of soda-saline soils. Specifically, the crack length has high correlation(R2 > 0.87) with the electrical conductivity(EC), Na+, CO32– and the salinity, it also has reasonable relationship(R2 > 0.68) with HCO3–, this indicates crack length can be well used for the prediction of these properties of soda-saline soils.

Economic Analysis of Diversified Rotational Cropping Systems in the Lateritic Belt of Lower Gangetic Plain of Eastern India

Economic analysis of different diversified rotational cropping systems under Farmers＇ package/practices and improved package/practices was conducted in Birbhum district, West Bengal, located in the red and lateritic belt of lower Gangetic plain of eastern lndia. Diversified triple cropping systems （peanut-brinjal＋brinjal, rice-potato-pumpkin, and cucumber-cabbage-basella） required higher cost for cultivation, but also produced higher rice equivalent yield, higher net return and higher return rupee1 invested in both management practices. Considering the resource-ability and risk-bearing capacity, and net return and return rupee^-1 （RPR） invested, these cropping systems can be recommended for resource-rich farmers. Rice-rapeseed-cowpea, rice-wheat-green gram and radish-tomato-amaranthus systems profitable. These cropping systems can be required less inputs for cultivation, were less risky, and economically viable and recommended for resource-poor farmers. Peanut-brinjal ＋ brinjal-okra-chilli ＋ chilli-cucumber-cabbage-basella system was the best among all the 3-year rotational systems in respect to RPR in both management practices. This rotational system will be suitable for resource-rich farmers. Vegetable-based rotational systems （ridge gourd-marigold-okra-black gram-pointed gourd ＋ pointed gourd-radish-tomato-amaranthus） or rice-based rotational system （rice-wheat-green gram-rice-rapeseed-cowpea-rice-potato-pumpkin） also found to be suitable to increase the profitability and system sustainability. These cropping systems can be recommended for all groups of farmers.