Mechanical performances and microstructural characteristics of reactive MgO-carbonated silt subjected to freezing-thawing cycles

The characteristics of reactive magnesia(MgO)-carbonated silt in respect to long-term stability have not been well understood in severely cold climate despite the usage of reactive MgO in enhancing the engineering performances.Under the binder content of 15% and initial water content of 25%,MgO-admixed silt specimens were carbonized for 3 h and 6 h and then subjected to different numbers of freezingthawing(F-T) cycles.After different F-T cycles,the physico-mechanical properties of MgO-carbonated silt were analyzed in comparison with Portland cement(PC)-stabilized silt through physical and unconfined compression tests.Besides,a series of micro tests on MgO-carbonated specimens was performed including X-ray diffraction(XRD),scanning electron microscopy(SEM) and mercury intrusion porosimetry(MIP) tests.The results demonstrate that both mass change ratio and moisture content of carbonated/stabilized silt decrease,and these values of MgO-carbonated silt are significantly lower while the density is higher compared to PC-stabilized silt.The strengths and moduli of MgO-carbonated silt are still two times higher than those of PC-stabilized specimens and the strength change ratio of keeps above0.8 after F-T cycles.There is no visible transformation between nesquehonite and dypingite/hydromagnesite,although the XRD peaks of nesquehonite decrease and the bonding and filling effects weaken slightly.After 6 and 10 F-T cycles,the pore-size characteristics changed from a unimodal distribution to a three-peak and bimodal distribution,respectively.The total,macro and large pore volumes increase obviously while the medium and small pore volumes decrease except for intra-aggregate pore.The findings show better F-T durability of MgO-carbonated silt,which would be helpful for facilitating the application of MgO carbonation in the soil treatment.     

Hydraulic conductivity profiling with direct push methods

Spatial variations in hydraulic conductivity (K) are a primary control on contaminant movement in groundwater, but characterization of these variations has proven difficult. Over the last two decades, significant progress has been made in utilizing Direct Push (DP) technology to characterize K variations in unconsolidated settings. Profiling methods have been developed based on empirical correlations between K and more readily evaluated formation properties and on the formation response to water injection or extraction. The latter (hydraulic) methods appear to have the most potential. Initial work on these methods involved adaptation of conventional well tests, but recent efforts have better exploited DP capabilities. The High-Resolution K and continuous Direct Push Injection Logger (DPIL) methods are the most promising approaches. Both provide high-resolution (0.015?m) K profiles, although the DPIL profile is only qualitative in nature. Currently, the K range of both is approximately 0.001 to 60 m/d, but that range should increase in the near future.     

Hydraulic conductivity of a glacial clay till liner

The study of water flow through soils is an important aspect of soil mechanics. Past experience with glacial clay till deposits investigated in central and southern Saskatchewan has demonstrated that in situ saturated hydraulic conductivities vary from about 10^?6 to 10^?9 cm/s. In some applications and regulatory references, an accepted practice in the past is to assume that the field hydraulic conductivity value for a soil liner will be one order of magnitude (i.e. ten times) greater than the confirmed laboratory hydraulic conductivity value for a remoulded sample composed of the same soil. In fact, experience has shown that measured as-built field hydraulic conductivity values for a soil liner can be several orders of magnitude greater than the laboratory value if the liners are poorly constructed and, therefore, would not be compliant with regulatory criteria. The reliability of artificially applying any correction factor to a laboratory value to obtain an assumed field value is, therefore, questionable. This paper describes field and laboratory investigations that were conducted to characterize the general properties and the hydraulic conductivity of a glacial clay till soil liner. For this example case study, laboratory measurements of the hydraulic conductivity for remoulded soil samples were undertaken using a flexible wall permeameter (FWP). Air-entry permeameter (AEP) tests were performed on a soil test pad prior to construction and then on the completed soil liner immediately after construction to measure the as-built hydraulic conductivity. Both the FWP and AEP tests resulted in comparable hydraulic conductivity values that were in the order of 10^?8–10^?9 cm/s. A preceding and preliminary empirical approach was also found to be reasonable for purposes of determining soil suitability and estimating the “achievable” hydraulic conductivity value. The preliminary estimate was determined to be conservatively greater than the values determined by both the FWP and AEP test methods.     

Hydraulic conductivity behaviour of soil blended with geofiber inclusions

Efficiency of fiber reinforcements to ensure the sealing efficiency of the landfill cap soil barriers so as to isolate the waste from the environment was demonstrated in the present study. Evaluation of hydraulic conductivity of soil barrier materials with different types of fibers, fiber dosage and fiber lengths are very important to ensure the sealing efficiency of the fiber reinforced soil barriers. An attempt was made to evaluate the hydraulic conductivity of the soil barrier material at a known effective stress using a flexible wall permeameter. Soil samples of 100 mm diameter and 100 mm height were prepared and tested in the present study. In all the cases, the hydraulic conductivity test phase was started after the completion of initialisation, saturation and isotropic consolidation phases of the soil samples. In the present study, seventeen (17) hydraulic conductivity tests were conducted on two different soil types for studying the influence of fiber content, fiber length and fiber type on the hydraulic conductivity of fiber reinforced soil. The fiber content, f used were 0.25%, 0.50% and 0.75% and the fiber lengths, l were 30 mm, 60 mm and 90 mm. Two types of fibers namely polyester (PET) fibers and polypropylene tape (PP-T) fibers were used for hydraulic conductivity tests. The repeatability of test results was also demonstrated. As the fiber content and fiber length were increased, initially there was a marginal decrease in hydraulic conductivity of the soil and thereafter marginally increased. Short fibers and low fiber contents were found to have greater influence in reducing the hydraulic conductivity of the soil and the variation was found to depend on the soil type also. Even with long fibers, the hydraulic conductivity of selected barrier material remained within the permissible limit required for a barrier material. The hydraulic conductivity of PP-T fiber reinforced soil is more, compared to hydraulic conductivity of PET fiber reinforced soil at all the fiber contents varied in the present study. The use of Scanning Electron Microscopy (SEM) is also attempted for the interpretation of the results.     

Hydraulic conductivity and pore sizes of nonwoven filter fabrics

This paper presents a method of determination of hydraulic conductivity and equivalent pore size of nonwoven synthetic filter fabrics. Piwowar's relationship for hydraulic conductivity, checked by Piwowar for glass and basalt fibres is given, and, on the basis of the transformation of Hagen-Poiseuille's formula, values of the empirical coefficients present in these formulae, the investigations on hydraulic conductivity and pore size of nine nonwoven filter fabrics were carried out. The numerical values of these coefficients and, after their substitution, the simplified formulae obtained for hydraulic conductivity and equivalent pore size of nonwoven synthetic filter fabrics are given.     

Hydraulic conductivity of geosynthetic clay liners to tailings impoundment solutions

The results of a comprehensive testing program conducted to evaluate the hydraulic conductivity (k) of two geosynthetic clay liners (GCLs) considered as a liner component for a tailings impoundment at a proposed zinc and copper mine are reported. The two GCLs were permeated with a relatively low ionic-strength ground water (GW) from the mine site and two electrolyte solutions, a process water (PW) and a simulated leachate (SL), with chemical compositions consistent with those expected during operation of the impoundment. A total of 22 flexible-wall tests were performed to determine the effects of prehydration with the GW, type of GCL, type of permeant liquid, and duration of the back-pressure stage of the test. The k values for both GCLs permeated with the GW were 1.7 × 10⁻⁹ cm/s, which is within the range 1–3 × 10⁻⁹ cm/s typically reported for GCLs permeated with low ionic-strength liquids, such as deionized water. However, the mean values of k based on permeation of duplicate specimens of both types of GCL with either PW or SL relative to the values of k based on permeation with GW, or k/k_w, ranged from a factor of 200 (2.3 orders of magnitude) to a factor of 7600 (3.9 orders of magnitude). Thus, both tailings impoundment solutions had significant adverse impacts on the hydraulic performance of both GCLs. Given the overall range of k/k_w values, factors such as prehydration, type of GCL, type of permeant liquid, and duration of back pressure, were relatively insignificant. The results of this study serve to emphasize the need to perform hydraulic conductivity testing using site specific materials.     

数值模拟在地下水水源地渗透系数反演上的应用

以南京市东郊备用地下水水源地为例,将数值模拟法与优化反演法相结合,建立了二维、非均质、各向异性及稳定流地下水数值模型,并通过优化反演,得到了水源地含水层的渗透系数场。     

活性粉末混凝土配合比及导电性能研究

通过改变水胶比、石英粉、石英砂等的掺量,研究了不同配合比活性粉末混凝土流动度、强度的变化规律.讨论了超细钢纤维、短切碳纤维不同掺量对活性粉末混凝土强度及电阻率的影响.结果表明:0.23水胶比的活性粉末混凝土,3d热养护抗压强度为181.97 MPa,抗折强度为30.14 MPa,工作性良好;活性粉末混凝土的电阻率随纤维掺量增加而不同程度减小.     

Hydraulic conductivity of two geosynthetic clay liners permeated with a hyperalkaline solution

GCLs containing powdered Na-bentonite treated with different dosages of a proprietary additive intended to reduce the impacts of chemical interactions were permeated with three solutions: a hyperalkaline solution (1 M NaOH and 1.3 mM CsCl) having similar pH to aluminum refining leachate, a 1.3 mM CsCl solution (no NaOH), and DI water. For a given permeant solution, the hydraulic conductivity of both GCLs was similar. Thus, the higher additive dosage had no measureable impact on hydraulic conductivity. Hydraulic conductivity of both GCLs decreased by a factor of approximately 1.5–1.8 during permeation with CsCl in response to osmotic swelling induced by the low ionic strength of the CsCl solution entering the pore space. In contrast, permeation with the NaOH–CsCl solution caused the hydraulic conductivity of both GCLs to increase modestly (<50 times the hydraulic conductivity to DI water), and then level out (or decrease slightly) as a result of reduced osmotic swelling in the interlayer combined with dissolution of the mineral. For the tests conducted with CsCl solution, nearly all of the Cs was adsorbed by the bentonite. In contrast, Cs broke through readily when the NaOH–CsCl solution was used as the permeant solution. Permeation with the NaOH–CsCl solution also increased the sodicity of the bentonite by replacing bound K, Ca, and Mg on the mineral surface.     

Hydraulic conductivity of bentonite-polymer composite geosynthetic clay liners permeated with bauxite liquor

The high ionic strength of the porewater in red mud (bauxite liquor from digestion) can suppress swelling of montmorillonite, resulting in geosynthetic clay liners (GCLs) that are too permeable to be effective as liners in red mud disposal facilities. Bentonite-polymer composite GCLs (BPC GCLs) have been developed as more resilient lining materials, and some BPC GCLs have been shown to have very low hydraulic conductivity to bauxite liquors that have extreme ionic strength and pH. In this study, a nationwide investigation was conducted in China to evaluate the characteristics of bauxite liquor in Chinese impoundments, and to evaluate the suitability of GCLs containing granular sodium bentonite or BPCs for containment. Hydraulic conductivity tests were conducted on six BPC GCLs with two characteristic Chinese bauxite liquors that are hyperalkaline (pH > 12) and had ionic strengths of 76.9 mM and 620.3 mM. The BPC GCLs had hydraulic conductivity ranging from 10^?8-10^?12 m/s, which is higher than the hydraulic conductivity of BPC GCLs to deionized water (10^?12-10^?13 m/s), but lower than the hydraulic conductivity of conventional GCLs with granular sodium bentonite GCLs to the same liquors (10^?7-10^?8 m/s). The hydraulic conductivity of the BPC GCLs depends on the chemical properties of the leachate, the polymer loading, and the type of polymer. Microstructural analysis by scanning electron microscopy (SEM) suggests that the hydraulic conductivity of BPC GCLs is controlled by pore-blocking by polymer hydrogel, which is affected by the bauxite liquor.     

粉土及稳定粉土的基本特性与工程应用研究

结合陇海铁路郑（州）徐（州）段电气化改造工程,对粉土的基本特性进行了研究总结,并对水泥、石灰及二灰稳定粉土的工程特性进行了分析对比,得出三种掺合料可以改良粉土工程性质,但改良效果程度不同,水泥比石灰的改良效果好,在掺合比相同的条件下,二灰比石灰的改良效果也要好的结论。     

关于淤泥质土的工程特性及其处理利用的综述

针对湖泊、河道的淤积问题、环境问题等矛盾日益突出的现状,探讨了河道淤泥的处理方法,并对淤泥的发展趋势进行了详细论述,指出加快淤泥资源化利用具有现实而深远的可持续发展的意义。     

Hydraulic conductivity of fly ash-sewage sludge mixes for use in landfill cover liners

Secondary materials could help meeting the increasing demand of landfill cover liner materials. In this study, the effect of compaction energy, water content, ash ratio, freezing, drying and biological activity on the hydraulic conductivity of two fly ash-sewage sludge mixes was investigated using a 2^7-1 fractional factorial design. The aim was to identify the factors that influence hydraulic conductivity, to quantify their effects and to assess how a sufficiently low hydraulic conductivity can be achieved. The factors compaction energy and drying, as well as the factor interactions material × ash ratio and ash ratio × compaction energy affected hydraulic conductivity significantly (α = 0.05). Freezing on five freeze-thaw cycles did not affect hydraulic conductivity. Water content affected hydraulic conductivity only initially. The hydraulic conductivity data were modelled using multiple linear regression. The derived models were reliable as indicated by R_adjusted² values between 0.75 and 0.86. Independent on the ash ratio and the material, hydraulic conductivity was predicted to be between 1.7 × 10⁻¹¹ m s⁻¹ and 8.9 × 10⁻¹⁰ m s⁻¹ if the compaction energy was 2.4 J cm⁻³, the ash ratio between 20% and 75% and drying did not occur. Thus, the investigated materials met the limit value for non-hazardous waste landfills of 10⁻⁹ m s⁻¹.     

非粘性土地基含淤泥包和夹层淤泥处理技术的分析

沙特红海地区RSGT项目场地吹填珊瑚礁非粘性土地基内局部分布淤泥包和成层、夹层淤泥,淤泥的性质较差且分布复杂,再加上工程远在海外,受施工条件限制所能够使用的地基处理方法很有限.为此,根据现场具备的施工条件,通过对岩土的性质和特点的分析,使用了水压振冲碎石桩联合强夯法处理深度小于14m的深厚淤泥包和较高夯击能的强夯法处理...     

粉土抗液化性能的微观分析

通过对不同粘粒含量和不同时间情况下的重塑粉土进行扫描电镜的实验分析,初步了解了其在不同粘粒含量下以及时效下的微观结构的变化规律,以及粉土的微观结构与其抗液化性能之间的关系。通过对粉土微观照片的分析,得出结论：含天然黏土颗粒的粉土,其微观结构特性在黏粒含量为Pc=9%附近发生变化。即黏粒含量Pc＝9％为粉土土性变化的－转折点。     

Structural characteristics and hydraulic conductivity of an eluvial-colluvial gravelly soil

Bulletin of Engineering Geology and the Environment - Gravelly soil is a typical heterogeneous porous medium with a multiscale structure and hydraulic conductivity that is challenging to quantify....     

粉土的动力特性研究

选用太原地区粉土为研究对象，通过粉土重塑土样的动三轴试验，研究了动荷载作用下围压、干密度及初始含水量对粉土重塑土样动弹模量目的影响，得出影响动弹模量的发展规律。     

建筑排水系统立管水力特征

为了防止有害有毒气体进入室内,介绍了排水立管的水流特点,分析了立管中的水流状态和影响立管内压力波动的因素,提出了改善压力波动的措施,从而保证室内的空气品质,并对工程实际具有指导意义。     

Flocculation of river silt using chitosan

Flocculation of silt in river water using chitosan was studied in the pH range 4-9, and suspended solid concentrations in the range 20-80 mg/L. Chitosan effectively reduces turbidity due to silt by flocculation and settling. Flocculation efficiency is very sensitive to pH, and reaches a maximum at pH 7. The optimal chitosan concentration required to effect flocculation is 0.5 mg/L and is independent of silt concentration within the range examined. Restabilisation of the suspension is observed at higher concentrations of chitosan, and the amount required for restabilisation increases with increasing concentration of suspended solids. Flocculation is faster at higher concentrations of silt and the flocs are large and fibrous.     

尾粉砂动模量阻尼试验研究

通过动三轴液化试验,研究了尾粉砂在等压固结和偏压固结下的一些力学特性,分析了动应变ε_d,固结压力σ_(3c),固结应力比E_d对动模量E_d的影响,得到了阻尼比与动应变的关系,为该尾矿库二次扩容设计提供了相关的力学特性依据。