磷石膏尾矿坝渗流场与稳定性分析

针对大峪口磷石膏尾矿坝的实际情况,设定多种运行工况。运用饱和-非饱和渗流理论,分析磷石膏尾矿坝在各种工况下的渗流场。渗流场分析结果表明,干滩长度变化以及排渗垫层的淤堵程度对浸润线的影响十分明显,干滩长度越长,坝体浸润线越低;排渗垫层淤堵越重,浸润线越高。在渗流场分析的基础上,运用饱和-非饱和边坡稳定性分析方法,对坝体进行稳定性分析,得出不同工况下坝坡的安全系数。坝坡稳定性分析结果表明,在当前实际运行坝高180m时,最小安全系数为2.27,坝体是稳定的。不同工况下的安全系数均满足技术规程的规定。     

高含水率疏浚淤泥透气真空防淤堵模型

透气真空技术解决了传统真空处理高含水率疏浚淤泥存在的淤堵问题,但其防淤堵控制尚缺乏有效分析方法.利用Ruth滤水理论建立了高含水率疏浚淤泥径向排水模型,采用透气真空抽水模型的试验结果验证了模型的有效性.同时,明确了反映淤泥排水层滤水性能的径向平均比阻arav在抽水过程中的变化规律:传统真空抽水形成的淤泥排水层有一个被压密的过程,孔隙结构不稳定,排水管道易发生淤堵;而采用透气真空抽水可以使淤泥排水层形成相对稳定的孔隙结构,有效地防止淤堵现象的发生.     

疏浚淤泥中的拱架结构防淤堵机理

透气真空快速泥水分离技术适用于高含水率高粘粒含量疏浚淤泥的堆场处理,可以快速减小堆场中淤泥的体积,加速堆场的周转利用,并能解决常规真空处理方法中存在的滤层淤堵问题。通过对透气真空快速泥水分离试验和常规真空抽水试验结束后进行试样取样颗粒分布试验,可以看出透气真空方法中滤层材料附近的淤泥土体中细颗粒流失,粗颗粒富集,形成拱架结构;而常规真空抽水方法中不存在细颗粒流失,没有形成拱架结构,造成了淤堵。分析了拱架结构层形成的过程,其能够保护土体内部的细颗粒不再流失,同时保证较高的渗透性。解释了常规真空抽水方法容易产生淤堵,而透气真空方法能够解决淤堵问题的原因。     

透水模板布水泥浆淤堵过程模拟分析

因依据现有过滤介质堵塞理论模型,建立出的透水模板布(CPFL)淤堵过程与颗粒过滤过程的关系均是定性的,并无法进行定量分析,故本文采用综合渗透排水能力测定仪,模拟混凝土浇筑时CPFL的淤堵过程,测试并计算得出CPFL淤堵过程中混凝土中多余水分通过CPFL的渗排速度v,CPFL淤堵程度f,时CPFL淤堵过程进行定量分析。     

循环往复水流条件下土工织物反滤淤堵机理探究

本文中通过进行循环往复水流条件下的梯度比试验,研究了三种不同开孔孔径的无纺土工织物分别作为反滤层时,其各自的反滤性能。通过分析被保护土体各部分渗透系数的变化来研究土工织物的反滤淤堵机理,探究了经典反滤理论在循环往复水流条件下的正确性、适用性和局限性。     

单向拉伸对土工织物反滤性能影响的试验研究

为研究单向拉伸对土工织物反滤性能的影响，选取两种条膜机织有纺织物和两种短纤针刺无纺织物，将不同拉应变下的织物与非连续级配土组成反滤系统，利用梯度比渗透仪测试系统反滤参数随拉应变的变化。根据反滤设计的透水、保土和防淤堵3个准则，分析拉应变对透水率、漏土量、梯度比等各参数的影响。试验结果表明：随着拉应变增加，有纺织物透水及防淤堵性能增强，保土性能减弱；无纺织物则相反，透水及防淤堵性能减弱，保土性能增强；同种土工织物厚度越大，拉应变对其反滤性能影响越大。     

某尾矿坝三维渗流及控制技术研究

为了研究某尾矿坝在被采挖至坝顶180m标高时的渗流情况,采用有限元法对其三维渗流情况进行分析,并给出相应控制措施。经分析得出:该尾矿坝渗流稳定性较差,存在溃坝风险;为有效控制浸润面,可在初期坝附近设置一道排渗墙。     

不透水地基上水平排渗体的优化研究

不透水地基上水平排渗体的优化研究沈振中，速宝玉（河海大学水力发电工程系，南京，２１００２４）１前言在水利工程设计中，渗流控制历来是至关重要的，尤其是土石坝、尾矿坝及灰坝，其渗流自由面的形态位置往往决定了工程的安全性。通常能有效控制自由面的渗控设施有竖...     

粗、细尾砂筑坝渗流特性模型试验及现场实测研究

以云南2个矿山生产的粗尾砂和细尾砂为堆坝材料,通过室内小比例渗流堆坝模型试验和现场实测,对粗、细尾砂在堆坝过程中渗流规律进行对比研究.研究结果表明:(1) 细粒尾砂堆积坝的浸润线较粗粒尾砂堆积坝高的原因有两方面:①细粒尾矿自身渗透性差;②在堆坝过程中,细粒尾砂在用于防漏作用的土工布上形成了一层较密实的防水层,堵塞了土工布排水小孔,阻碍了尾矿坝排渗效果;(2) 粗、细粒尾矿堆积坝的坝前沉积规律基本相同,即同一水平面上为前缘细后部粗,上部粗下部细,但粗粒尾矿堆积坝形成的干滩面坡度较大,为1.0%～2.5%,而细粒尾矿堆积形成的干滩面坡度比较平缓,为0.3%～0.9%;(3) 根据尾矿坝的整体排渗效果,提出"尾矿坝相对渗透率"的概念,在外部条件基本相同的情况下,细粒尾砂堆积坝的相对渗透系数约为粗尾砂堆积坝的25%;(4) 由于细粒尾矿渗透性较差,浸润线偏高,造成尾矿坝坝坡水头压力较大,极易引起坝坡渗透破坏.研究成果对类似尾矿堆坝的研究具有重要的指导意义.     

无纺土工织物压缩回弹变形试验研究

本文对无纺土工织物的变形特性、变形指标、变形计算,以及保持足够透水性的织物允许受力强度进行了试验研究,并为实际工程中的织物合理选用、透水性校核、滤层及垫层排水设计提供了具体方法和途径。     

Permeability prediction in geotextile envelope after chemical clogging: a coupled model

This study develops a coupled model of chemical clogging and permeability coefficient of geotextile envelope. Based on the distribution characteristics of crystal precipitates on geotextile envelope and their influence on the permeability coefficient, a permeability coefficient model of an actual geotextile envelope that considers the overlapping effect is developed. Then, the densification effects of geosynthetic fiber hypothesis and the filter cake effect hypothesis are proposed to simulate the processes of increasing fiber diameter after crystal precipitation and the accumulation of crystal precipitates on the surface of geotextile envelope. The crystal precipitation module and permeability coefficient module are coupled, and their experimental values are used to confirm the availability of the model. Results indicate the satisfactory performance of the model. In addition, the parameter sensitivity analysis and trend prediction show that the saturation index SI and solution flow rate V are the main factors that affect the chemical clogging and permeability of geotextile envelope. When the solution conditions are not considered, the sensitivity of geotextile envelope parameter d_f increased with the amount of precipitation in crystal precipitation. When the pores of the geotextile envelope are completely clogged, the permeability coefficient of the geotextile envelope will drop sharply, then decline slowly.     

Modelling of hydraulic deterioration of geotextile filter in tunnel drainage system

The discharge capacity of a tunnel drainage system generally decreases with time because of the hydraulic deterioration of the geotextile filter. Hydraulic deterioration restricts groundwater flow into a tunnel and increases water pressure resulting in detrimental effects on the tunnel lining. Hydraulic deterioration of tunnel drainage system is unique in terms of clogging materials, deterioration mechanism, and flow conditions. Current studies and models investigating the clogging mechanism and hydraulic deterioration are not directly applicable to the geotextile filter of the tunnel drainage system. In this study, a theoretical model of the hydraulic deterioration of tunnel geotextile filter has been proposed considering the mechanical and hydraulic behavior of blinding, clogging and squeezing. A parametric study was carried out to evaluate the performance of the model. An experimental study has been conducted to investigate the clogging behavior of the tunnel drainage system and validate the theoretical model. Several types of clogging materials were selected: cement-leaching calcium oxide, calcium carbonate, iron oxide, and bentonite. Agglutinated clogging was mainly observed during the short-term testing. The findings suggest that the in-plane permeability of the geotextile filter decreased by approximately 90%. The proposed model corroborated the experimental results.     

Tailings-nonwoven geotextile filter compatibility in mining applications

Nonwoven geotextiles have been commonly used in filtration and drainage of geotechnical engineering works. This paper presents a study on the use of such materials in drainage and filtration systems of tailings dams. Different combinations of tailings and geotextiles were submitted to gradient ratio (GR) tests under confinement in the laboratory with varying values of stress levels and hydraulic gradients. The results of GR tests under confining stresses up to 2000 kPa are presented and discussed. The dimensions of the tailings particles entrapped in the geotextile specimens and those that piped through the geotextile were also assessed. Geotextile specimens from the drainage system of a tailings dam were exhumed for analyses, as part of the research programme. The results obtained showed that stress levels and the hydraulic gradients used in the tests influenced the behaviour of the system. Physical and microscopic analyses of the specimens tested showed greater geotextile impregnation by tailings particles in the field than in the laboratory. The overall performance of the geotextiles tested under laboratory conditions was satisfactory. However, in the field segregation of tailings particles and transport of fines in suspension can subject the filter to more complex and severe clogging mechanisms, not properly simulated in current standard testing procedures.     

A study on biological clogging of nonwoven geotextiles under leachate flow

This paper presents results of long-term permittivity tests using leachate to evaluate biological clogging of nonwoven geotextiles. Three types of geotextiles with varying masses per unit area were used in the tests. The identification and quantification of microorganisms in the geotextile were carried out as well as microscopic investigations. The accuracies of semi-empirical models to evaluate the kinetics of bacteria growth and to correlate hydraulic properties and microbiological parameters were examined. Permittivity tests under increasing water heads were also performed on the geotextile samples already subjected to long-term leachate flow in order to evaluate the values of water heads required to wash the biofilms out of the geotextile pores. The results of the tests showed the marked reduction of geotextile permeability due to biological clogging and that the results of the predictions by semi-empirical methods were consistent with the biological mechanisms observed.     

Influence of clogging substances on pore characteristics and permeability of geotextile envelopes of subsurface drainage pipes in arid areas

This study investigates the influence of clogging substances on pore characteristics and permeability of geotextile envelopes that were used for 3, 7 and 15 years in irrigated farmlands in Xinjiang region, which is arid and suffers from the soil salinity problem. Results show that the macropores (above 125 μm) of envelopes are evidently clogged, whereas the smaller pores less than 100 μm are still unblocked after operation. The permeability coefficients of geotextile envelopes after serving for 3 and 15 years are smaller than the minimum required permeability coefficients after clogging. The main chemical components of clogging substances in the geotextile envelope are silicon dioxide and calcium carbonate. Calcium carbonate content of the geotextile envelope is consistent with calcium carbonate content of soil. Chemical clogging susceptibility increases with the operation time of the subsurface drainage pipes. The ratio of O₉₀ size of envelope material over d₉₀ of soils (O₉₀/d₉₀) and saturation index (SI) can be used to assess the susceptibility of physical and chemical clogging respectively. This study provides a preliminary reference for estimating the clogging susceptibility of geotextile envelopes in arid areas.     

Removal of particulate matter and phosphorus in sand filters treating stormwater and drainage runoff: a case study

Runoff is often delayed and treated in wet ponds to retain particles and particulate substances. To increase the treatment efficiency, a sand filter can be placed before the outlet. The filter material is often renewed after 10–15 years due to presumed clogging by trapped particles, but often it clogs much earlier. Knowledge of how clogging develops over time is therefore important. This study has examined two filters, focusing on particle size, content and placement of particles, organic matter (OM) and phosphorus (P) retained in the filter. The study concludes that both particles and P are retained in the upper few cm’s of the filter, causing clogging after a few years, thus leaving the deeper filter material unused. Even small particles (<63 µm) are efficiently retained as long as clogging is avoided. This is preferable, as runoff is rich in small particles and as particulate P is associated with the small particles.     

CFD-DEM modeling of geotextile clogging in tunnel drainage systems

In this study, a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) method we used to investigate the hydraulic deterioration of a geotextile due to clogging in tunnel drainage systems. Initially, a framework was developed to generate and test a numerical representation of a typical non-woven geotextile. Following model validation, we carried out parametric analysis to examine the effect of fine content, crack angle, and groundwater inflow. The results showed a general trend of pressure increase associated with increasing both the crack angle and fine content. This increase was found to decay at larger crack angles and high content of fines. Interestingly, increasing groundwater inflow was found to had minimal effect on the final deposition of the clogging particles. Finally, an approximate semi-analytical model was developed to describe the pressure increase due to clogging. The model was able to provide a good match with the data obtained from the numerical analysis.     

The effect of submersion in the ochre formation in geotextile filters

This analyzes the effect of submersion in the formation of ochre biofilm in geotextile filters used in drainage systems. The chemical microbiological aspects involved in ochre formation and clogging of drainage systems are discussed. Clogging by ochre may be considered a major threat in the performance of filters and drainage systems. This process has been observed in the field and demonstrated in laboratory tests under well-controlled conditions. Oxygen is needed for ochre formation and is available at the water–air interface of the filters. If the filters are submerged, oxygen may also be available dissolved in the water, with higher concentrations close to the surface due to the diffusion process. Column filter tests with the introduction of iron bacteria under three different filter submersion conditions were carried out. Woven geotextile filters were used in all tests. Biofilm formation on the geotextile filters were evaluated through the analysis of EDS (Energy Dispersive X-ray detector) and scanning electron microscopy. Ochre formation was verified in all tests, confirming that ochre formation can occur even under submerged conditions. The formation of ochre biofilm decreased with the depth of the geotextile filter in relation to the water surface, following the expected reduction of available oxygen below the water surface.     

Design of non-woven geotextiles for coal refuse filtration

This paper presents research findings on grain size distribution changes of coal refuse affecting the design of non-woven geotextiles used as filters in rock drains at coal waste impoundments. The research involved performing hydraulic conductivity tests on refuse - geotextile filters followed by grain size distribution tests. Data was evaluated for geotextile filter retention, permittivity, and clogging potential requirements as published by the U.S. Mine Safety and Health Administration’s Second Edition, “Engineering and Design Manual Coal Refuse Disposal Facilities”.Key findings indicate that refuse particles undergo slaking and aggregation which change the initial grain size distribution. Grading envelopes were developed and indicate that particle size zones influence the geotextile design parameters for retention, filtration, and clogging. The clogging criteria do not appear to be easily satisfied by the typical ranges of coarse coal refuse, at pre- and post-compaction grain size, for compatibility with non-woven geotextiles having an AOS = 0.212 mm.Conclusions impacting the specification and field installation of geotextiles include: i) post grain size distribution tests are suggested to be performed on specimens and at all compaction levels to observe changes in key indices of D₈₅ and D₁₅ for meeting retention and clogging criteria requirements; ii) the evaluation of the initial refuse stability indicate that at the low compaction energy conditions, which have mobile fines and high Cu values, are initially unstable with regards to their internal soil gradation; and iii) construction of geotextile wrapped drains is preferred to be made in pre-compacted refuse lifts. This condition is beneficial because the filter becomes more stable for retention and permeability; however clogging is still a concern.     

Clogging of stormwater gravel infiltration systems and filters: insights from a laboratory study

Stormwater infiltration systems are widely used in the control of polluted urban runoff. They are very effective in reducing the volume of stormwater runoff and improving its quality, but they are known to be prone to clogging. Whilst it is evident that clogging determines the design lifespan of infiltration systems, quantitative understanding of the clogging process is currently very limited. A laboratory study was therefore undertaken to better understand physical clogging processes, with the ultimate aim of developing a clogging model for stormwater infiltration systems. This paper presents findings from one-dimensional (1-D) experiments conducted on a gravel filter column. Physical clogging was studied under both constant and variable water levels, and for different sediment inflow concentrations. It was found that a clogging layer forms at the interface between the filter and underlying soil, irrespective of the inflow regime of both water and sediment. It was also found that clogging is much slower if the water level is kept at a constant level than if it varies within the column, due to formation of a sediment plug that 'shelters' the filter/soil interface. Most importantly it was shown that physical clogging is mainly caused by migration of sediment particles less than 6 microm in diameter. A simple regression model was proposed and tested for the prediction of clogging due to stormwater sediment.