Factors affecting the performance of drainage envelope materials in structurally unstable soils

Rather subjective criteria are applied for the need and kind of drainage envelope material to use. To gain more information on the performance of envelope materials in structurally unstable soils, flow tests were carried out in vertical soil columns filled with an unstably aggregated silt loam soil. To discover the most unfavourable situation in evaluating envelope materials, experiments with both downward and upward flow were performed. Also tests were carried out to find out the effect of soil sample height. Further, factors affecting soil aggregate stability, such as the initial moisture content and the hydraulic gradient, were considered. Two soil aggregate conditions, sensitive to degradation, were used in the investigation of the performance of both coarse and fine-textured envelopes.     

Research and developments in selecting subsurface drainage materials

Subsurface drainage requires appropriate materials to ensure a proper functioning of the drainage system. The materials normally applied for subsurface drainage are drain pipes and envelopes. Besides a review of the materials used for drain pipes, their hydraulic characteristics — discharge capacity and entrance resistance — have been treated. Much attention is paid to subsurface drainage envelope materials because of practical problems and a serious gap in knowledge, in spite of considerable research efforts. After treating the aim of drainage envelopes, a review of the used materials is given. Practical experience with gravel envelopes, still often used in irrigated areas, shows serious shortcomings. Since organic envelopes are vulnerable to deterioration, the only possible alternative are synthetic envelopes. Their property to retain soil particles is characterized by the so-called filter criteria. Laboratory research and field experiments to evaluate the blocking and clogging aspects of synthetic envelopes are discussed and selection criteria given.     

扬州沿运灌区暗管排水土工布外包滤料的水力性能试验研究

农田暗管排水系统建设是提高农业机械化作业效率的有效措施之一.土工布作为排水暗管外包滤料时,需要具有良好的透水性能和抗淤堵能力.文中以扬州段沿运灌区为例,针对当地土壤中粉粒含量较高,土工布外包滤料筛选困难等实际问题,参考相关技术准则,选用2种开孔率和厚度不同的土工布进行了水力渗透试验,并与传统的河砂反滤材料进行了对比,筛选出适合当地土壤的土工布外包材料.研究结果显示,所选用的2种土工布透水性能存在较大差异,其中厚度较大(0.41 mm)、孔径较小(180 μm)的土工布A的透水性能较好,渗透系数为初始值的54.1%,高于河砂滤层的46.1%,而厚度为0.35 mm、孔径为227 μm的土工布B渗透系数仅为初始值的30.2%.相比于土工布B,土工布A具有更好的抗淤堵能力,长期使用后淤堵率比土工布B低16%.通过对土工布表面形成的、透水性较低的滤饼分析发现,土工布B不但自身发生了较大程度淤堵,其表面形成的滤饼较为密实,是影响其渗透性能的直接原因.     

The hydraulic effect of filter materials around gappy non-ideal field drains

The analyses of Widmoser and of Kirkham for flow into gappy non-ideal drain pipes with longitudinal slits and circumferential openings, respectively, were modified to take into account the hydraulic effect of filters when the boundary between filter material and soil is an equipotential surface. Upper and lower bounds were found for the effective drain radii of the drain pipes when surrounded by a cylindrical filter, by calculating the effective drain radii of the drain pipes with filter surrounds whose outer boundaries are the equipotential surfaces just contained within and without the outer cylindrical surface of the filter. The calculated bounds are close to each other for large filter thicknesses, but become further apart as the filter thickness is decreased. These calculated bounds for the effective radius were used to calculate, by the hodograph method, lower and upper bounds for the maximum water-table height for parallel lines of drain pipes installed in an infinitely deep soil. These show that the maximum water-table height in drained land is considerably lowered in the presence of a filter more permeable than the soil surrounding a gappy nonideal drain, and that a thin filter of high hydraulic conductivity relative to the soil is hydraulically more beneficial than a thicker filter of hydraulic conductivity only slightly more than that of the soil. An exact analysis, useful only for large filter thicknesses, is also given for the flow towards pipe drains with circumferential openings when surrounded by permeable material with hydraulic conductivity varying inversely with radial distance.     

Opening floodgates in coastal floodplain drains: effects on tidal forcing and lateral transport of solutes in adjacent groundwater

The effects of opening tidal barriers (floodgates) upon water table levels and lateral transport of solutes adjacent drains was investigated at two sites on a coastal floodplain. The sites had contrasting geomorphology, soil texture and sediment hydraulic properties. The site with lower hydraulic conductivity (0.3–0.9 m day⁻¹) soils (Romiaka) also had a higher elevation and hydraulic gradients towards the drain. While floodgate opening at Romiaka enhanced the amplitude of pre-existing tidal interaction with adjacent shallow groundwater, altered hydraulic gradients and caused some salt seepage, lateral solute movement from the drain was highly attenuated (<10 m). The site with very high hydraulic conductivity soils (Shark Creek; >125 m day⁻¹) had a lower elevation and seasonally fluctuating hydraulic gradients. The introduction of a tidal pressure signal into the drain by opening the floodgate at Shark Creek caused tidal forcing of groundwater over 300 m from the drain. Floodgate opening at this site also caused changes in groundwater hydraulic gradients, leading to incursion of saline drain water into shallow groundwater over 80 m from the drain. Lateral movement of solutes was relatively rapid, due to macropore flow in oxidised acid sulfate soil horizons, and caused substantial changes to shallow groundwater chemical composition. Conversely, when groundwater hydraulic gradients were towards the drain at this site there was substantial lateral outflow of acid groundwater into drains. This study highlights the importance of assessing the hydraulic properties of soils next to drains on coastal floodplains prior to opening floodgates, particularly in acid sulfate soil backswamps, in order to prevent unintended saline intrusion into shallow groundwater.     

双吸离心泵叶轮无损反求设计研究

介绍了进口MABS双吸离心泵叶轮的无损反求设计研究过程。根据反求工程理论，进行该叶轮的结构反求设计、CAD辅助水力性能反求设计和工艺及材料的反求设计。反求设计的MABS叶轮现场运行平衡，水力性能指标达到原型水泵的性能。     

外包滤料对暗管排水与土壤脱盐效果的影响

为了探究不同外包滤料条件下的暗管排水性能和土壤脱盐效果,基于室内试验研究成果,在田间设置4种暗管排水系统(各系统中暗管埋深均为80 cm,间距均为20 m),所用外包滤料分别为68 g/m²土工布(L)、砂滤料(S)、68 g/m²土工布+砂滤料(LS)和无外包滤料(W),以当地常规明沟排水(CK)作为对照,通过田间试验分析了春灌过程中各暗管系统的排水性能指标及土壤脱盐效率.结果表明:相比处理W,处理L,S和LS平均排水速率提升了7.44%,12.55%和15.75%,平均流量衰减度降低4.07%;处理S和LS累积排水量提高了5.11%和8.31%(P<0.05).各暗管处理春灌后平均土壤脱盐率均达47%以上,较CK提升显著,其中处理LS效果最优,为50.94%.综上,应优先选择处理LS作为河套灌区暗管排水系统外包滤料布设方案.该研究结果可为河套灌区暗管排盐技术的推广应用提供理论支撑和科学指导.     

涌泉根灌灌水器外壳材料对水力性能的影响

对使用ABS、纯HDPE、HDPE+20%EVA、LDPE+20%EVA以及40%HDPE+40%LDPE+10%LLDPE+10%EVA这5种不同外壳材料制造的涌泉根灌灌水器,从外壳材料的收缩率、弹性模量、拉伸应变特点等方面研究了外壳材料对涌泉根灌灌水器出流特性的影响.结果表明,外壳材料对涌泉根灌灌水器的水力性能影响明显:外壳材料的模塑收缩率越大,灌水器外壳与内芯流道贴合越紧密,流量就越小;灌水器外壳的刚性越强,即材料的弹性模量越大,不同压力作用下灌水器的流量相差越小;相同制造工艺下,外壳材料的自然回弹率影响灌水器的制造偏差,材料的回弹性越好,得到的灌水器流量偏差越小.因此,为了得到制造偏差小、水力性能良好的涌泉根灌灌水器,对外壳材料的选配应平衡刚性及自然回弹性.推荐使用混合材料40%HDPE+40%LDPE+10%LLDPE+10%EVA用以制备涌泉根灌灌水器外壳.     

隔膜计量泵的改良设计与汽蚀性能的提高

针对应用于石油化工装置上的进口隔膜计量泵容易产生的汽蚀问题，对隔膜泵复合隔膜、柱塞密封副、液压平衡与补偿阀结构进行了改良设计，采用较大承载能力的机座、独特阶梯式活塞、加大直径的活塞、PTFE＋NBR复合隔膜，改良放气安全阀及油浸没式补偿系统等方法，提高了隔膜计量泵的汽蚀性能；通过对改造的隔膜计量泵与原有的计量泵进行的汽蚀试验对比，给出了隔膜计量泵性能与现场使用的最佳匹配工况。改良的结构设计和新型材料的选用大大提高了计量泵的汽蚀性能。     

Diagnosis of mineral clogging hazards in subsurface drainage systems

The paper presents a global review of drain clogging hazard criteria. Some of them are simple granulometric formulae, some include an evaluation of soil structural stability, and some others are based on laboratory tests which reproduce water-flow through a soil core. A recent development is then described. Terzaghi's theory of critical hydraulic gradient explains structural break-up of soil samples by water-flow towards drain pipes. Based on this theoretical approach, a laboratory test has been designed to determine experimental values of the hydraulic gradient causing soil breaking. This test is used to compare the stability of different soil materials and to diagnose mineral clogging hazards.Due to the existence of numerous granulometric criteria there is evidence that no global criterion can be found. If a proper granulometric criterion is suited to a given climatological and pedological context, the hydraulic laboratory test is probably the most cost-effective method to diagnose mineral clogging hazard, especially when no field references are available.     

Y型网式过滤器多目标优化正交试验

为了提高Y型网式过滤器水力性能和抗堵塞性能,以出口与筒体间夹角、入口缩小比、导流片高度和导流片圆心角为试验因素,采用CFD-DEM耦合和物理试验相结合的方法对过滤器内部的过滤过程进行探究。通过系列数值模拟正交试验结果的极差分析探索各因素对水头损失、中速过流量区域面积占比、颗粒分布相对标准偏差及拦截率4个指标影响的敏感度,结果表明：中、高速过流量区域均集中在出口侧,当出口与筒体间夹角越小时,出口截面积与其呈正相关,且对应中速过流区面积越大,水力性能越好。颗粒集中通过区域与中速过流量区域相对应,入口缩小比的增大使颗粒分布越均匀,抗堵塞性能越好。结构优化参数组合为：出口与筒体间夹角35°、入口缩小比22/26、导流片高度10mm、导流片圆心角90°,其中夹角对综合指标影响最为显著,是结构设计的关键参数。与改进前相比,水头损失减小了36.6%,相对标准偏差减小了43.26%,拦截率提高了3.93个百分点,中速过流量区域面积占比增加了15.77个百分点,表明了优化方案的有效性。研究结果可为网式过滤器的优化设计提供参考。     

心墙堆石坝水力劈裂可靠性分析方法及应用

首先利用水力劈裂判断准则,构造心墙水力劈裂功能函数;然后根据坝体材料物理参数的概率分布类型,采用几何法计算心墙水力劈裂可靠指标,得出心墙发生水力劈裂的概率。实例分析结果表明,蓄水初期,心墙上游面中部发生水力劈裂的概率较顶部和底部大;随着心墙材料的泊松比、密度变异性的增加,心墙发生劈裂破坏的概率也相应增加;弹性模量对心墙水力劈裂影响程度较小;降低蓄水速度可以降低心墙发生水力劈裂的概率。     

心墙堆石坝水力劈裂可靠性分析方法及应用

首先利用水力劈裂判断准则,构造心墙水力劈裂功能函数;然后根据坝体材料物理参数的概率分布类型,采用几何法计算心墙水力劈裂可靠指标,得出心墙发生水力劈裂的概率。实例分析结果表明,蓄水初期,心墙上游面中部发生水力劈裂的概率较顶部和底部大;随着心墙材料的泊松比、密度变异性的增加,心墙发生劈裂破坏的概率也相应增加;弹性模量对心墙水力劈裂影响程度较小;降低蓄水速度可以降低心墙发生水力劈裂的概率。     

Identification of the hydraulic conductivity using a global optimization method

A method to determine the soil hydraulic conductivity via an internal drainage experiment is presented. Identifying the parameters of the hydraulic conductivity is achieved by solving an inverse global optimization problem that uses the water contents measured at different depths and times as matching flow variables. The optimization procedure is combined with a recently developed analytical model for the water content propagation, which essentially assumes that the flow is gravity-driven. A crucial (from the identification point of view) parameter of such a model is the initial position z_W of the draining front, determining the interface between the wetted and dried zone. By using an evolutionary algorithm specifically developed for this problem, it is shown that if information upon z_W is not a priori available, the identification of the hydraulic conductivity is not possible. However, assuming that z_W is known (i.e. measured), and by dividing the model variables by z_W, the optimization is able to fully identify the soil hydraulic conductivity. Finally, in order to show the robustness of the proposed approach, it is shown that the method leads to very good estimates of the hydraulic conductivity even if data are noise-affected, provided that the optimization procedure is coupled to the (Tikhonov) regularization approach.     

Granular envelope research in Pakistan

In 1989, research on granular envelope design for subsurface horizontal pipe drains was started when existing design procedures for envelope design did not result in successful application of a granular envelope (crushed rock) material at the Fourth Drainage Project. Although construction problems were, in part, the reason for the failure of the crushed rock envelope, it was also found that standard design criteria need additional rules to prevent a similar occurrence of failure. Tests were performed in the laboratory with permeameters, sieves, and other equipment and preliminary results are reported. The effect of number, size and arrangement of perforations on the test results are indicated. Test results of blended granular materials such as crushed rock, river-run gravel and sand from various sources in Pakistan are outlined.Proceedings of 5th International Drainage Workshop, Lahore, Pakistan, ICID-CIID, IWASRI, 1992, Vol. III, 5.38–5.49.     

In situ water transmission characteristics of a tropical soil under rice-based cropping systems

In soils under rice-based cropping systems in Asia water movement and distribution in the root zone of rice and dryland crops are important for efficient water management. Saturated hydraulic conductivities in the wetland soil profile were evaluated from measurements of hydraulic gradients and percolation rates in the field. The subsoil layer (15–60 cm) restricted percolation rate to a greater degree than the puddled top soil.Unsaturated hydraulic conductivities and soil water diffusivities in the soil profile under dryland conditions were obtained from simultaneous measurements of soil water content using the neutron moderation technique and the soil matric potential by tensiometers over time and soil depth. Soil matric potential versus hydraulic conductivity and soil water content versus soil water diffusivity relations of various soil depths were established. At equivalent soil matric potentials, the hydraulic conductivity of surface soil was greater than that of the subsoil layers. Soil water diffusivity at different depths responded similarly. The study describes a simple in situ technique to measure percolation rates in wetland rice fields and evaluation of water transmission properties of field soil profiles.     

基于Android平台的土壤采样信息自动记录系统

目前土壤采样信息大多依赖于实验人员手动纸质记录。为了更好地记录和处理土壤信息,提出了一种适用于现代化农业的土壤采样信息记录方法,利用Android系统结合服务器和数据库架构实现基于Android的土壤采样信息自动记录系统。整个系统设计包括系统架构设计和软件功能设计。在服务器上使用JSP和MySQL数据库管理系统（Database management system,DBMS）作服务器端,搭建云服务器及农田信息管理数据库。服务器端设计包括在WEB工程中引入JDBC驱动,使服务器直接连接数据库,实现WEB服务器与MySQL数据库的交互。Android客户端设计包括在Material Design设计规范下完成土壤自动采样记录系统Android客户端界面,以及利用JSON数据解析实现对云服务器下MySQL数据库信息的访问和操作。最后对系统软件进行有效性和健壮性测试。试验表明,该系统能有效地显示采样土壤位置的空气温度、湿度、经纬度以及土壤氮素含量等土壤采样信息,并能进行正确的地图位置显示,证明了Android系统在土壤采样记录方面的有效性以及构建系统的可行性。     

Comparative effects of chemical amendments on salt and NA leaching

Summary Efficiency of sodic soil reclamation is thought to vary with types of chemicals used. This study examined the effects of five inorganic (H₂SO₄, CaCl₂ · 2H₂O, CaSO₄ · 2H₂O, FeSO₄, Al₂(SO₄)₃) and two organic compounds (polyacrylamide, and trihydroxy glutaric acid) on the rate and the extent of salt and Na leaching in moderately Na-affected saline soils: Saneli silty clay loam (Vertic Torrifluvents, ESP=17.5%) and Glendale silty clay (Typic Torrifluvents, ESP=13.5%). Air-dry soil samples (<2mm) were packed in columns, and chemicals, except H₂SO₄, were incorporated into the surface 5 cm of the soils, and in selected cases, to 30 cm. H₂SO₄ was surface-applied. Application rates of the inorganic chemicals were 3.57 and 10.7 mmol(+) kg^-1 (2.5 and 7.5 Mg ha^-1 in gypsum equivalent weight) in the silty clay loam, and 8 and 24 mmol(+) kg^-1 in the silty clay, and the organic compounds were applied at rates of less than 620 kg ha^-1. The soils were then leached with simulated Rio Grande water (EC = 1.1 dS m^-1, SAR = 3.5) under continuous ponding. The tested inorganic compounds removed approximately equivalent amounts of exchangeable Na after approximately 35 cm of water application. However, the rate of water percolation (consequently the rate of salt leaching) from CaCl₂ treated columns, became progressively slow after about 20 cm of water intake. The combined effect of rapid electrolyte leaching and insufficient replacement of Na in the surface layer seemed to be responsible for the flow reduction. Gypsum and H₂SO₄ treatments provided lower ratios of sodicity to salinity in percolating solutions and relatively uniform hydraulic gradients throughout the soil depth. Incorporation of chemicals to the surface 30 cm did not alter performance, except in CaCl₂ treatments where water intake rates became even slower. The tested organic amendments improved initial water infiltration, but neither increased subsequent percolation rates nor improved salt and Na leaching. The fastest reclamation may be attained when chemicals are chosen and applied to yield an electrolyte concentration that is high enough to overcome Na effects at any depth of soil profiles throughout the leaching period.Contribution from Texas Agr. Expt. Sta. Texas A & M University System. This project was supported in part by the Binational Agricultural Research and Development (BARD) Fund and the Expanded Research Area Fund of the Texas Agricultural Experiment Station.     

Spatial analysis of soil surface hydraulic properties: Is infiltration method dependent?

The management of irrigated agricultural fields requires reliable information about soil hydraulic properties and their spatio-temporal variability. The spatial variability of saturated hydraulic conductivity, K_s and the alpha-parameter α_vG-2007 of the van Genuchten equation was reviewed on an agricultural loamy soil after a 17-year period of repeated conventional agricultural practices for tillage and planting. The Beerkan infiltration method and its algorithm BEST were used to characterize the soil through the van Genuchten and Brooks and Corey equations. Forty field measurements were made at each node of a 6 m × 7.5 m grid. The soil hydraulic properties and their spatial structure were compared to those recorded in 1990 on the same field soil, through the exponential form of the soil hydraulic conductivity given by the Gardner equation, using the Guelph Pressure Infiltrometer technique. No significant differences in the results obtained in 1990 and 2007 were observed for either particle-size distribution or dry bulk density. The mean value of α_vG-2007 was found to be identical to that of α_G-1990, while that of K_s-2007 was significantly smaller than that of K_s-1990. In contrast to the Gardner equation, the van Genuchten/Brooks and Corey expression was found to be more representative of a well-graded particle-size distribution of a loamy soil. The geostatistical analysis showed the two parameters, K_s and α_vG-2007, were autocorrelated up to about 30 and 21 m, respectively, as well as spatially positively correlated within a range of 30 m. Despite the difference in the mean values of K_s between the two studies, the spatial structures were similar to those found in the 1990 experiment except for the covariance sign. The similarity in autocorrelation ranges indicate that the spatial analysis of soil hydraulic properties is independent of the infiltration methods (i.e., measurement of an infiltration flux) used in the two studies, while the difference in the covariance sign may be linked to the use of two different techniques of soil hydraulic parameterization. The covariance values found in the 2007 campaign indicates a positive relationship between the two parameters, K_s and α_vG-2007. The spatial correlations of soil hydraulic parameters appear to be temporally stabilized, at least within the agro-pedo-climatic context of the study. This may be attributed to the soil textural properties which remain constant in time and to the structural properties which are constantly renewed by the cyclic agricultural practices. However, further experiments are needed to strengthen this result.     

三维仿真及Java在拖拉机液压零件设计中的应用

为了提高拖拉机液压系统零部件设计的效率,将三维仿真软件和Java技术引入到了零部件的设计方案中,采用Pro/E软件实现了拖拉机液压零部件的设计和建模,并使用参数化设计方法提高了设计效率,利用成熟的Java技术建立了模型库和数据库的接口,实现了零件库数据的访问和各种网络应用,开发出一个具有扩展功能的网络化液压系统零件库。以普通拖拉机千斤顶液压系统的设计为例,对零件库系统的功能进行了测试,结果表明:采用三维仿真和Java建立的零件库系统可以完成拖拉机液压系统阀缸体的参数化设计,并可以显示缸体的装配图与爆炸图,实现液压回路的原理设计,为拖拉机液压系统的快速设计提供了一种新的方法。