Application of HYDRUS-1D in understanding soil water movement at two typical sites in the North China Plain

Recharge and discharge, such as rainfall infiltration and evapotranspiration in vertical direction, are major processes of water cycle in the shallow groundwater area of the North China Plain. During these processes, soil water movement in the unsaturated zone plays an important role in the transformation from rainfall infiltration to groundwater. The soil water movement models were developed by using HYDRUS-1D software at two typical experimental sites in Cangzhou(CZ) and Hengshui(HS) with different soil, vegetation and similar climate conditions. As shown in the results, the comparison in precipitation infiltration features between the two sites is distinct. The soil water experiences strong evaporation after precipitation infiltration, which accounts for 63% of the total infiltration at the HS site where the soil is homogenous. It is this strong evaporation effect that leads to slight increase of soil water storage. At the CZ site, where the soil is heterogeneous, the evaporation effect exists from July to October of the simulation period. The total evaporation accounts for 33% of the total infiltration, and the evaporation rate is slow. At the end of the simulation period, the soil water storage increases and the water table decreases, indicating a strong storage capacity at this site.

Effects of biochar on water movement characteristics in sandy soil under drip irrigation

Biochar addition can improve the physical and hydraulic characteristics of sandy soil.This study investigated the effects of biochar on water holding capacity and water movement in sandy soil under drip irrigation.By indoor simulation experiments,the effects of biochar application at five levels(0%,1%,2%,4%and 6%)on the soil water retention curve,infiltration characteristics of drip irrigation and water distribution were tested and analyzed.The results showed that biochar addition rate was positively correlated with water holding capacity of sandy soil and soil available water.Within the same infiltration time,with an increasing amount of added biochar,the diffusion distance of the horizontal wetting front(HWF)tended to decrease,while the infiltration distance of vertical wetting front(VWF)initially declined and then rose.The features of wetted bodies changed from"broad-shallow"to"narrow-deep"type.The relationship between the transport distances of HWF and VWF and the infiltration time was described by a power function.At the same distance from the point source,the larger the amount of added biochar,the higher the soil water content.Biochar had a great influence on the water content of the layer with biochar(0–200 mm)and had some effects at 200–250 mm without biochar;but it had less influence on the soil water content deeper than 250 mm.For the application rate of biochar of 4%,most water was retained within 0–250 mm soil layer.However,when biochar application amount was high(6%),it would be helpful for water infiltration.During the improvement of sandy soil,biochar application rate of 4%in the plow layer had the best effect.

Effect of Polyacrylamide Application on Water and Nutrient Movements in Soils

An understanding of nutrient movement in soil is important for developing management strategies to minimize nutrient leaching and surface movement, thus improving nutrient uptake by plants, maintaining a sustainable soil system, and even protecting groundwater quality. Polyacrylamide (PAM) is known as one of soil conditioner that functions to stabilize soil structure, increase infiltration, and reduce surface runoff. This study assesses the effects of PAM on the vertical movement of soil-water and major/minor nutrients (NO3-N, NH3-N, T-N, PO4-P, T-P, K, Ca, Mg, and Fe) in soils. Saturated hydraulic conductivity (Ksat) increases with increasing PAM concen- trations up to 10 mg·L-1 for sand and 20 mg·L-1 for a mixture of sand and clay. Decreases in the loss of soluble nutrients, particularly NH3-N, PO4-P and T-P, are observed as PAM concentrations increase. In contrast, PAM concentration has no effect on nitrate and minor nutrient levels. These results indicate that the application of PAM may be a viable method for protecting water bodies from excessive nutrients and improving nutrient availability for plants.

堆载下深厚软土侧移分析及响应面预测方法研究

为预测路堤堆载作用下的土体侧移,为土位移法计算既有高铁桥梁桩基内力及侧移提供条件,本文采用Midas GTS建立二维有限元模型,计算路堤填筑产生的土体侧移,分析土体参数、路堤参数及堆载空间位置等因素对土侧移的影响。对各因素进行敏感性分析,采用响应面法,以5次多项式构建土体侧移与各因素之间的显式关系式。结果表明:路堤填筑后,土层总位移呈“灯泡”形,侧移沿深度方向呈现“弓”形;土体最大侧移随着土体泊松比、路堤堆载等级、路堤填筑宽度增加而增大,随距路堤中心距、土体弹性模量增大而减小;土体侧移对土体泊松比、路堤堆载等级、土体弹性模量、路堤填筑宽度、距路堤中心距离较敏感,对下层岩体的泊松比等因素不敏感;拟合得到的响应面函数可准确预测不同堆载等级下深厚软土土体侧移。研究结果便于快速估算堆载下土体侧向位移。

考虑非达西渗流的泥浆离心脱水分析

为深入探究离心脱水技术在处理主要由黏性土组成的建筑废弃泥浆时的内在机理及其影响因素,利用分段线性化方法,充分考虑黏性土中渗流的非达西特性以及土体变形的非线性特征,建立在离心作用下能够考虑其非达西渗流特性的泥浆脱水分析模型。通过与已有研究成果及室内试验结果的对比,证明了该模型的有效性。在此基础上,分析了模型参数对脱水过程的影响。研究结果表明:脱水速度和最终土水界面位移量随着电机转速的增大而增大;增加泥浆初始厚度会增大最终土水界面位移量,但会降低初期的土水界面移动速度;压缩指数在初期对土水界面位移的影响并不明显,但其增大会导致最终土水界面位移量的增加;非达西渗流参数的增大会导致土水界面位移的减少,但通过提升电机转速,可以有效地降低非达西渗流对脱水效果的不利影响。研究成果可为离心脱水技术在建筑废弃泥浆处理中的进一步优化与应用提供借鉴和参考。

Finite element analysis of effect of soil displacement on bearing capacity of single friction pile

Effect of soil displacement on friction single pile in the cases of tunneling,surcharge load and uniform soil movement was discussed in details with finite element method.Lateral displacement of the pile caused by soil displacement reached about 90% of the total displacement,which means that P-Δ effect of axial load can be neglected.The maximum moment of pile decreased from 159 kN·m to 133 kN·m in the case of surcharge load when the axial load increased from 0 to the ultimate load.When deformation of pile caused by soil displacement is large,axial load applied on pile-head plays the role of reducing the maximum bending moment in concrete pile to some extent.When pile is on one side of the tunnel,soil displacements around the pile are all alike,which means that the soil pressures around the pile do not decrease during tunneling.Therefore,Q-s curve of the pile affected by tunneling is very close to that of pile in static loading test.Bearing capacities of piles influenced by surcharge load and uniform soil movement are 2480 kN and 2630 kN,respectively,which are a little greater than that of the pile in static loading test(2400 kN).Soil pressures along pile increase due to surcharge load and uniform soil movement,and so do the shaft resistances along pile,as a result,when rebars in concrete piles are enough,bearing capacity of pile affected by soil displacement increases compared with that of pile in static loading test.

Finite element analysis of couple effect of soil displacement and axial load on single inclined pile

The couple effect of soil displacement and axial load on the single inclined pile in cases of surcharge load and uniform soil movement is discussed in detail with the methods of full-scale field tests and finite element method. Parametric analyses including the degree of inclination and the distance between soil and pile are carried out herein. When the displacement of soil on the left side and right side of a pile is identical, deformation of a vertical pile and an inclined pile is highly close in both cases of surcharge load and uniform soil movement. When the couple effect of soil displacement and axial load occurs, settlement of an inclined pile is greater than that of a vertical pile under the same axial load, and bearing capacity of an inclined pile is smaller than that of a vertical pile. This is quite different from the case when the inclined pile is not affected by soil displacement. For inclined piles, P-Δ effect of axial load would lead to a large increase in bending moment, however, for the vertical pile, P-Δ effect of axial load can be neglected. Although the direction of inclination of piles is reverse, deformation of piles caused by uniform soil movement is totally the same. For the inclined piles discussed herein, bending moment(-8 m to-17 m under the ground) relies heavily on uniform soil movement and does not change during the process of applying axial load. When the thickness of soil is less than the pile length, the greater the thickness of soil, the larger the bending moment at lower part of the inclined pile. When the thickness of soil is larger than the pile length, bending moment at lower part of the inclined pile is zero.

龙川县米贝村1^(#)泥石流灾害特征与运动过程

受区域气流影响,广东省龙川县在2019年6月10—13日出现持续强降雨天气,累计降雨量超过260 mm,从而引起全县发生大量滑坡、泥石流灾害。以米贝村1^(#)泥石流为研究对象,在野外调查认识基础上,结合Fluent数值分析对这类低山丘陵区的小型泥石流灾害运动特征展开研究。研究发现:米贝村1^(#)泥石流受沟床粗糙度、纵坡降、流向等因素影响,其流速具有动态变化特征,总体表现为先增大再减小的发展趋势,泥石流物质的变化对其运动速度有一定影响。在整个过程中最大流速可达9.77 m/s,平均速度为3.31 m/s,与实际调查结果相符。研究成果不仅可直接为米贝村重在区灾后工程防治提供指导,对于东南沿海相似地区的降雨型滑坡-泥石流灾害的研究具有借鉴作用。

灌溉量和垄高对次生盐渍地玉米土壤水盐运移变化及产量的影响

为探究宁夏扬黄灌区因多年地面灌溉引起的地下水位上升、次生盐渍化突显等难题,本试验以宁夏红寺堡移民区为研究点,选定典型试验区域开展定位试验监测,设置高效滴灌下不同灌溉量(2160、2700 m^(3)·hm^(-2)和3240 m^(3)·hm^(-2))和起垄高度(20、30 cm和40 cm)2个因素3个水平,通过大田试验研究不同组合处理下的次生盐渍地水盐运移变化规律以及其对玉米生长指标、产量和水分利用效率的影响。结果表明,灌水定额一定时,随垄高增加,0~60 cm土层含水率逐渐降低;相同垄高下,随灌水定额增大,各土层含水率逐渐增加,并且深土层明显高于浅土层。垄作滴灌可以有效降低垄上土壤盐分含量,而各处理土壤深层均不同程度积盐,其中T9处理(3240 m^(3)·hm^(-2)和40 cm组合)40~60 cm土层积盐最明显。T6处理(2700 m^(3)·hm^(-2)和40 cm组合)各项生长指标及产量均优于其他各处理,产量达6597.15 kg·hm^(-2),T5(2700 m^(3)·hm^(-2)和30 cm组合)水分利用效率最高,达到1.53 kg·m-3。通过回归分析发现,玉米产量最大值时和水分利用效率(WUE)最大值时的灌水量和垄高值不同,进一步利用空间分析方法得出,灌水量2685~2730 m^(3)·hm^(-2)和垄高36~39 cm时,玉米产量、WUE均达最大值的90%以上。

Seed movement of bare alkali-saline patches and their potential role in the ecological restoration in Songnen grassland, China

The dynamics of soil seed banks and seed movement was investigated in three bare alkali-saline patches in Songnen grassland, Northeast China, for exploring their potential role in the vegetation restoration of bare alkali-saline patches. The results showed that the seed banks and the seed movement in these patches were very similar to each other, and to some extent the seed movement was related to patch-side vegetation there. Seed movement across the soil surface of these bare alkali-saline patches was abundant and dominated by the seeds of pioneer species, such as Chloris virgata and Suaeda corniculata, which accounted for over 96% of these trapped seeds. In the contrast, soil seed banks of bare patches were extremely small, in different seasons, especially in May and June, even no any seed have been found, mainly due to lowest retaining capacity of surface soil to those abundant seed movement. Both soil seed banks and seed movement showed seasonal variation, and usually reached the maximum in October. Soil seed banks of bare alkali-saline patches, which were extremely small and difficult to recruit naturally, may inhibit speed of vegetation restoration. It is suggested that seed movement would be the potential seed source and play a potentially important role in the process of vegetation restoration of bare alkali-saline patches by enhancing the soft retaining capacity to seed movement.

Impact of Soil Type Used in Tunneling on Land Subsidence and Mobility Effective Time under Different Earthquake Records

During recent decades, tunnels construction in urban environments has been recognized as a useful factor in improving transportation situation in cities. Construction of underground structures like tunnels has a direct impact on the above-ground structures. The most important impacts are soil crust movement of the structure movement), acceleration change of the earthquake on structures, and land subsidence. The present research aims at seismic evaluation of the effect of soil type in land subsidence and effective mobility time in tunneling projects. For this purpose, two different soil types are chosen to model and assess factors using numerical methods. The outcome of this research concludes that tunneling changes in the dominant frequency record if these changes reach to the extent that structure frequency equals to record frequency, resonance phenomenon happens.

WATER AND SALT MOVEMENTS IN SIMULTANEOUS FLOOD-IRRIGATION AND WELL-DRAINAGE OPERATIONS

This paper describes a new technology for solonchak soil reclamation in which surface flood irrigation of fresh water and pumped wells drainage of salty groundwater are combined. The comprehensive investigation of water and salt movement has been conducted through field test, laboratory simulation and numerical calculation. The dependence of desalination on irrigation water quantity, drainage quantity, leaching time and other parameters is obtained based on the field tests. The entire desalination process under the flood-irrigation and well-drainage operations was experimentally simulated in a vertical soil column. The water and salt movement has been numerically analysed for both the field and laboratory conditions. The present work indicates that this new technology can greatly improve the effects of desalination.

An united model and simulation of nitrogen transport, uptake and transformation in soil-crop system

Based on the simulation experiments of water and nitrogen transport, transformation and uptaking, under the condition of different cropping pattern of winter wheat in the greenhouse and the condition of different wastewater irrigation plan. An united computing model of crop growth, distribution of roots, water and nitrogen uptaking by roots and transformation in soil crop system was developed. Growth status of crops, root growth condition and water, nitrogen uptaking pattern by roots under different watering and N pollution conditions were simulated and analyzed due to the development of this mathematical model and the identification of parameters and boundary conditions in the greenhouse, so that it provided a primary computing method for selecting an efficient, productive watering and wastewater irrigating plan.

A Porous Simulation Experiment of Protozoa Movement with Glass Bead

Protozoa can move due to their flagella, cilia or pseudopodia, and play an important role in the transformation and cycling of matter and energy in ecosystems. In this study, the glass beads with the diameters of 1. 0, 0.5, 0. 25 and 0.1 mm were used to simulate soil pores of 0. 292 - 0. 258, 0.155 - 0.116, 0.056 - 0.040 and 0.028 - 0.020 mm respectively. Three typical soil protozoa of Bodo edax, Colpoda cucullus and Amoeba proteus were examined for the relation of their movement to pores. It was found that the smallest protozoan of Bodo edax could be leached through all the pores. However, no more than 26% of the added protozoan was leached out of the column. The leached protozoa were decreased with the pore sizes and leaching duration. The bigger one of Colpoda cucullus was moved out from the column filled with the glass beads of > 0. 5 mm in diameter. Less than about 15% of the added protozoa were leached out of the column. The biggest one of Amoeba proteus could not leached out from any of the pores. It is evident that most of the protozoa remained in the column due to their occupation of the pores.

THE DESTRUCTION OF ANCIENT ECOLOGICAL ENVIRONMENT AND THE MOVEMENT OF CIVILIZATION CENTER IN CHINA

China is one of the ancient civilization countries. Owing to the blind reclamation, the vegetation had been destroyed, causing soil erosion and desertification, and making the civilization center move to the Changjiang (Yangtze) River valley from the Huanghe (Yellow) River. This movement began in the Qin and Han dynasties (221 B.C-220 A.D.) because at that time the large-scale reclamation was felled, the grassland was reclaimed into farmland, the vegetation was seriously destroyed in the loess and north of the Huanghe River, and the climate was getting colder; and the turn from north to south occurred in the Sui and Tang dynasties (581-907 A.D.) and completed in the Song Dynasty (960-1279 A.D.). However, at present the vegetation damage of the Changjiang River valley is very serious too and the silt carrying capacity of the Changjiang River is increasing sharply; thus the Changjiang River is in danger of becoming a second Huanghe River, so we must pay attention to the protection of ecological

基于EDEM的秸秆—土壤颗粒翻埋运动仿真及试验

水稻秸秆与土壤翻埋过程是影响秸秆还田的重要因素。在前期建立的还田刀辊—土壤—水稻秸秆三者仿真互作模型的基础上,进一步研究土壤颗粒的运动状态。在耕深为20 cm、刀轴旋转速度为240 r/min、单位秸秆量为3.5 kg/m2时,以秸秆翻埋率和还田深度为指标,分别进行仿真与室内模拟试验,翻埋率分别为87.5%、86.7%,还田深度分别为19.16 cm、18.68 cm,模拟试验验证仿真试验的有效性。仿真结果显示所标定颗粒152658与刀辊接触时,开始向后下方位移,到达最低点后随着刀辊的旋转向后上方抛洒,此时运动轨迹近似抛物线,随后在重力作用下回落到地表,与其他颗粒碰撞产生波动,直至最终停下。通过随机标定颗粒研究土壤受力情况,结果表明:当弯刀在开始接触土壤颗粒时,颗粒X、Y、Z方向受力均直线上升,最大值分别为15.61 N、37.2 N、50.37 N,直到该土壤颗粒团被弯刀切碎后,力逐渐下降为0。同理标定秸秆颗粒45 681,分析其运动轨迹,仿真结果表明:起初土壤颗粒对秸秆速度产生促进和抑制双重作用,随着土壤回落地表,秸秆在土层下主要受到土壤摩擦作用,直至秸秆速度降为0。仿真分析从微观角度揭示弯刀对秸秆翻埋还田的工作机理,为部件优化设计提供理论支持。

Integrated numerical model of nitrogen transportation,absorption and transformation by two-dimension in soil-crop system

A series of simulation experiments of nitrogen transportation, absorption and transformation were conducted, and the different cropping patterns of winter wheat and wastewater irrigation plans were taken into consideration. Based on the experiments, an integrated model of crop growth, roots distribution, water and nitrogen absorption by roots, water and nitrogen movement and transformation in soil-crop system by two-dimension was developed. Parameters and boundary conditions were identified and an effective computing method for optimizing watering and wastewater irrigating plans was provided.

微润灌多重变水头下土壤水分动态演变与数值模拟

为研究水头多重调控下微润管出流与土壤水分运移规律,进行了不同水头调控模式下微润灌入渗试验,设置调增(0→1 m(水头由0 m调节到1 m,以下类推)、0→2 m、1→2 m)和调减水头(1→0 m、2→0 m、2→1 m),研究微润管出流、湿润体及含水率变化规律;将微润管假定为多孔介质重黏土,利用HYDRUS 2D模型对水头多重调控下微润管出流和土壤水分运移进行了模拟,据此分析了多重变水头情景下微润灌土壤水分动态规律。结果表明,水头调节显著改变累积入渗量、入渗率与时间关系曲线,累积入渗量曲线呈折线型,曲线斜率随着调增或调减而有规律增减;水头调节导致入渗率发生骤增或骤降,稳定入渗率与水头存在线性正相关关系。调增水头时湿润锋内含水率骤升,正向反馈显著;水头调减后管周含水率微弱下降后逐渐回升。将微润管模拟为质地黏重的多孔介质,基于HYDRUS 2D模型较好地模拟了微润管出流及水分运移,优度较好(决定系数R2≥0.90,纳什效率系数(NSE)大于等于0.70,相对标准偏差(RSR)趋近于0)。构建了多重水头调控模式(0→1→2 m、0→2→1 m、1→0→2 m、1→2→0 m、2→0→1 m、2→1→0 m),分析了多情景下微润灌土壤水分动态规律,发现水头调增后入渗率随时间呈现“指数减小后稳定”规律,而调减后入渗率表现为“指数增加后稳定”;连续调增0→1→2 m方案下,最终累积入渗量最大;连续调减下(2→1→0 m)累积入渗量较调增方案降低3.7%,可通过调控水头控制湿润锋推移和湿润体内含水率分布,且微润管附近含水率对水头调控响应更为显著。研究可为微润灌动态水头调控提供科学依据,并与智慧灌溉相融合实时调控水头,适量地补给作物需水并维系根区适宜水分环境,实现精准灌溉。

非稳定渗流条件下宽级配砂砾土细粒迁移试验研究

既有的土体内部稳定性判定准则,对宽级配砂砾土非稳定渗流中的内部稳定状态难以准确刻画。从细粒迁移显微观测的试验设计中,通过测算试样流速与累计侵蚀率的突变特征,引入孔隙率n修正Istonima准则。研究结果表明:①细粒活跃状态随不均匀系数C u及孔隙率n的增加而增加,根据其运动特征可划分为稳定、过渡和不稳定3个阶段。②流速发展为存在渗流突变点的随水力梯度先减后增的非线性过程,渗流突变点是渗流压密—渗流侵蚀的转化临界点;试验中各因素对质量侵蚀率敏感性大小为:水力梯度、级配不均匀度、孔隙率,在C_(u)=20.47、n=0.40时质量侵蚀率最大。③通过对比以试样内部细粒稳定程度及宏观参数特征所划分的内部稳定性判定结果与各判定准则结果,将相对准确的Istonima准则进行修正,提高了对宽级配砂砾土内部稳定性的判定准确性。

ERT与TDR联合反演层状土壤水分运动过程

土壤水是地表水与地下水联系的纽带,是物质输送和运移的载体,在土壤-植物-大气(SPAC)系统中起着关键性的作用。土壤水分运动是一个非常复杂的过程,为充分了解水分在土壤中的运动过程,应用微扰动的高密度电阻率仪(ERT)监测了一层状结构的土壤剖面在注水入渗试验前、后不同时刻的电阻率的变化过程;同时,用时域反射仪(TDR)测量了点尺度上土壤体积含水量,建立了土壤电阻率和含水量的定量关系。结果表明,高密度电阻率法能够较为准确地监测土壤水分入渗深度和剖面含水量,土壤水分运动以向下的垂向运动为主并伴有微弱的水平流动;当土壤含水量低于0.15 cm^(3)·cm^(-3)时,随着含水量的增大,电阻率变化较大;当土壤含水量较高时,电阻率随含水量的变化不明显;根据建立的电阻率和含水量的定量关系公式,估算出在土壤界面处当上层土壤质量含水量达到0.136 g·g^(-1)时水分开始向下层入渗,相关研究成果为定量分析土壤水在分层界面处的变化情况提供了一种新的方法。