Potassium Chloride Treatment to Control Alkali Induced Heave in Black Cotton Soil

The results presented in this paper shows that high concentrations of sodium hydroxide causes abnormal changes on the volume change behaviour of illite–smectite (interstratified mineral) soil due to mineralogical changes. The higher swell that occurs is shown in the form of a new second stage of swelling. Increase in negative charges on soil particles and mineralogical changes after interaction with soil, respectively, are responsible for the swelling in these two stages. However, potassium hydroxide does not induce such high swelling in soils. This is mainly due to the fixation of potassium ions. Hence an attempt has been made to control the swelling induced by sodium hydroxide by making used of potassium chloride as an additive. Potassium fixation which is not substantial at neutral pH is favoured at higher pH Addition of potassium chloride salt solution (as 2 and 5% solution) can reduce only the first stage of swelling by linking the unit layers of mineral by reducing development diffuse double layer near clay surface. Potassium chloride is unable to prevent the formation of mineralogical alteration due to soil alkali interaction and hence the swelling associated with mineralogical changes. X-ray diffraction studies have revealed that mineralogical changes leading to formation of zeolite by soil alkali interaction is not inhibited by potassium ions. Morphological changes studied by scanning electron microscope corroborate these observations. Also the compressibility of soil which is increased in alkali solution is reduced in the presence of potassium salts. This reduction is due to reduction in the first stage of swelling.     

Mineralogical changes and geotechnical properties of an expansive soil interacted with caustic solution

The type and amount of clay mineral plays an important role in the behaviour of fine-grained soils. Clay minerals are the primary source and moisture is often the external agent of swelling in soils. Also soils may exhibit increased/reduced swelling due to interaction with chemicals. Alkalis used in industrial operations are one such example. Concentrations of alkali and mineral type are the key factors in such interactions. The present paper reports the changes in the properties of an expansive Black Cotton soil containing a mixed layer mineral, rectorite upon interaction with high concentration caustic solutions. X-ray diffraction studies have shown that the rectorite present in the soil undergoes changes with increase in the concentration of alkali. Saponite gets transformed to nantronite. Small amount of kaolinitic mineral present in the soil also reacts with alkali producing some changes in its mineralogy. Many hydroxides are produced. Differential thermal analysis studies have been supportive of these changes. Consequent of these changes, the soil-specific surface increases, changes its Atterberg limits and free swell volume increases. The results have been supported by the characteristics and behaviour of samples contaminated in the field with alkali from an alumina extraction plant.     

Crystalline and Osmotic Swelling of an Expansive Clay Inundated with Sodium Chloride Solutions

Compacted expansive clays swell due to crystalline swelling and osmotic/double layer swelling mechanisms. Crystalline swelling is driven by adsorption of water molecules at clay particle surfaces that occurs at inter-layer separations of 10–22 Å. Diffuse double layer swelling occurs at inter-layer separations >22 Å. The tendency of compacted clay to develop osmotic or double layer swelling reduces with increase in solute concentration in bulk solution. This study examines the consequence of increase in solute concentration in bulk solution on the relative magnitudes of the two swelling modes. The objective is achieved by inundating compacted expansive clay specimens with distilled water and sodium chloride solutions in free-swell oedometer tests and comparing the experimental swell with predictions from Van’t Hoff equation. The results of the study indicate that swell potential of compacted expansive clay specimens wetted with relatively saline (0.4, 1 and 4 M sodium chloride) solutions are satisfied by crystalline swelling alone. Comparatively, compacted clay specimens inundated with less saline solutions (0.005–0.1 M sodium chloride) require both crystalline and osmotic swelling to satiate the swell potential.     

Swelling characteristics of compacted lateritic soil–bentonite mixtures subjected to municipal waste leachate contamination

Compacted soil–bentonite mixtures are finding wide application as buffer material for waste repositories for their favorable self-sealing qualities. The swelling properties of such materials which serve as a measure of their self-sealing capabilities and, thus, the efficiency of the repository in sealing off their contents from the environment are closely related to the chemistry of the leachate that emanate from the wastes. For this reason, the swelling parameters (namely swelling potential and pressure) of compacted lateritic soil–bentonite mixtures under consideration for use as barrier in municipal waste landfill were evaluated. Series of swelling potential and pressure tests were performed using variable content (0–10 %) of bentonite at predetermined optimum moisture content. Soil mixtures were compacted with British Standard Heavy compactive effort and saturated with processed tap water as well as three leachate solutions of varying ionic strength that were generated in active open dump landfills. Experimental results showed that swelling potential based on the free swell together with the maximum swell pressures of compacted soil mixtures measured at equilibrium increased approximately linearly with increase in the amount of bentonite when inundated with processed tap water and the three leachate solutions. On the other hand, these swelling parameters decreased as the ionic strength of the leachate solutions measured by their electrical conductivity increased for the various soil mixtures. These results provide an insight into the swelling behavior and the possible degradation in the efficiency of the proposed lateritic soil–bentonite mixtures in relation to their use as buffer material in waste landfills.     

Impact of Carpet Waste Fibre Addition on Swelling Properties of Compacted Clays

Municipalities and recycling and environmental authorities are concerned about the growing amount of carpet waste produced by household, commercial and industrial sectors. It is reported that 500,000 tonnes of carpet waste fibre are plunged into landfills annually in the UK. In the United States of America, around 10 million tonnes of textile waste was generated in 2003. In geotechnical engineering, expansive clay soils are categorised as problematic soils due to their swelling behaviour upon increase in the moisture content. The problematic nature of such soils is intensified with the increase in the plasticity index. This paper presents results of a comprehensive investigation into utilisation of carpet waste fibres in order to improve the swelling characteristics of compacted cohesive soils. Therefore, two different clay soils with markedly different plasticity indices (i.e. 17.0 and 31.5 %) were treated with two different types of carpet waste fibre. Waste fibres were added to prepare specimens with fibre content of 1, 3 and 5 % by dry weight of soil. Soil specimens with different dry unit weights and moisture contents were prepared so as to the swelling behaviour of fibre reinforced compacted clays is completely attained under various scenarios. The results indicated that the behaviour of the fibre reinforced soils seems highly dependent on the initial compaction state and secondary on the moisture content. It was found that the swelling pressure drops rapidly as the percentage of fibre increases in samples prepared at the maximum dry unit weight and optimum moisture content. Reducing the dry unit weight, while maintaining constant moisture content or increasing the moisture content at constant dry unit weight was found to reduce the swelling pressure.     

渤海湾风暴潮倒灌对沿岸农田土壤盐分的影响

2003年10月11日渤海湾沧州范围内发生特大温带风暴潮,其摧毁沿岸养殖场后涌向沿海农田区域,海水倒灌农田浸泡持续时间达10~15 d不等。2004年5月3日,对浸泡农田土壤采样进行盐分分析,结果表明,经海水浸泡后农田全部盐碱化,且盐分主要聚集在土壤表层;46%的土地出现碱斑,0~90 cm土体内土壤含盐量较浸泡前普遍增加,0~10 cm表层含盐量高达1.134%;浸泡后0~25 cm土体内含盐离子组成较之浸泡前有显著变化,Cl－含量增加了33.3%,Na++K+含量增加了39.4%;降雨淋溶可以使土壤盐分含量明显下降,且为主要影响因素;经过一年后,土壤盐分含量降低到0.308%,而两年后,受灾土壤盐分含量降低到0.265%左右,可以种植耐盐性较强的作物。     

Relative performance of lime stabilized amended clay liners in different pore fluids

Successful design of soil liner and covers for landfills and waste impoundments involves selection of liner material and assessment of chemical compatibility of the liner material. In this work locally available materials with different mineralogy have been evaluated from the viewpoint of liner application. Many local soils may not meet the requirements of liner material; often it is necessary to amend these soils with commercially available processed bentonite. Clay liners may be attacked by chemical waste or leachate, concentrated organic chemicals can attack compacted clay effectively destroying the characteristics of liner material. Thus the main aim of this work has been to assess the suitability of different types of locally available materials for their potential use as liners for waste containment facilities. The materials studied are kaolinitic red earth, illite and fly ash. Based on literature survey and experimental work in this laboratory, 20% by weight of bentonite has been chosen for amending selected materials. Addition of 20% bentonite to selected liner material improved the hydraulic conductivity and adsorption capacity of the amended mixture but, reduced the volume stability. To improve the volume stability of the amended material and to have better resistance towards chemicals attack, stabilizing the amended mixture with 1% by weight of lime has been considered. The relative advantages and disadvantages of four materials namely; red earth with 20% bentonite, illite with 20% bentonite, fly ash with 20% bentonite and illite alone, stabilized with 1% by weight of lime were brought out. The chemical compatibility of the materials to electrolyte solution (0.5 N NaCl), alkaline solution (0.5 N NaOH), acid (0.5 N HCl) and organic fluid (CCl₄) has been studied. The relative efficiency of the selected materials with selected pore fluids was compared.     

Free-Swell and Swelling Pressure of Unsaturated Compacted Clays; Experiments and Neural Networks Modeling

Expansive soils have received attentions of several investigators in the past half of century in the problematic soils context. Volume change behavior of unsaturated compacted soils in presence of water and change of degree of saturation was observed in two form of heave or collapse. Low water content and low density compacted soils in presence of enough surcharge pressure lose stability and collapse, because of their metastable and susceptible structure to change of degree of saturation. Free-swell and swelling pressure of five compacted clays, covering low to high plastic clays have been investigated in respect to compaction states and swelling pressure was compared with collapse pressure threshold. The results of experiments were utilized in two Artificial Neural Networks to predict free-swell percent and swelling pressure of a soil sample based on index properties and compaction state.     

The impact of natural ornamental limestone dust on swelling characteristics of high expansive soils

Expansive soils are considered as a potential natural hazard if they are not adequately treated. Expansive soils have high potential for shrinking and swelling under changing moisture conditions and cause extensive damages to engineering infrastructures. This study is concerned with the suitability of natural ornamental limestone dust to reduce the swelling characteristics of high expansive soils. The results are revealed that the swelling pressure and percent of heave are greatly decreased with increasing the inserted core diameters and mixing percentages of limestone dust. The average reduction percent values of swelling pressure and percent of heave are increased from 2.21% to 43.09% and from 2.56% to 45.64%, respectively, for treated soil samples with increase in limestone dust core diameters from 5 mm to 20 mm (1% to 16% of total soil area). The average reduction percent values of swelling pressure and heave percent are increased from 10.29% to 70.73% and from 22.29% to 82.90%, respectively, for treated soil samples with increase in limestone dust mixing percentages from 10% to 30%. The results are revealed that the enhancement in swelling characteristics of high expansive soils that are treated by ornamental limestone dust is mostly attributed to the replacement of high expansive fine clay particles by non-expansive and non-plastic coarse limestone dust particles, and to the presence of a considerable amount of free lime in limestone dust (4.97% as [Ca(OH)₂]) that is responsible for converting the high expansive soils to less expansive soils by pozzolanic reaction. The mixing treatment method is more suitable for surficial and shallow foundation high expansive soil beds, while the compacted limestone dust piles “inserted limestone dust core method” are more suitable for deep foundation high expansive soil beds.     

中膨胀土CMA改性室内试验研究

CMA是一种新型膨胀土生态改性剂,依托合(肥)－六(安)－叶(集)高速公路工程,对CMA改性后中膨胀土的基本物理性质、击实特性、胀缩特性、力学特性等进行了3种配方的室内对比试验研究。结果表明,中膨胀土经CMA改性后,其自由膨胀率由改性前的71 %下降到20 %左右,液限和塑性指数也显著降低,亲水能力大幅度下降;胶粒含量明显下降,粉粒含量增加,说明改性后粒度组成已接近粉土;各项胀缩性指标较改性前也有大幅度下降,无荷膨胀率约为改性前的2 %,膨胀力约为改性前的5 %;改性土的CBR值可达50 %,浸水变形不到1 %;在非饱水和饱水状态下,改性土都具有较高的抗剪强度和无侧限抗压强度,说明改性后其水稳定性较好。经对比分析,认为1#配方改性效果最好,较适用于合肥膨胀土的改性处理。     

Insight into the effects of clay mineralogy on the cyclic behavior of silt–clay mixtures

Results of a systematic testing program showed that the cyclic behavior of silt–clay mixtures is greatly influenced by the dominant clay minerals in the mixture. In particular, it was demonstrated that given the same amount of clay/clay mineral and/or same value of plasticity index, the montmorillonitic soils have the highest cyclic strength, followed by the illitic soils, and then by the kaolinitic soils. Moreover, the rate of increase in cyclic strength with increasing % clay mineral and PI is again the highest in the montmorillonitic soil, lowest in the kaolinitic soil and intermediate in the illitic soil. Therefore, without considering clay mineralogy, the % clay fraction, % clay mineral and plasticity index are unreliable indicators of the liquefaction susceptibility of fine-grained soils. The differing adhesive bond strength each clay mineral develops with the silt particles is deemed to largely explain the observed differences in the response of the three different soil mixtures to cyclic loading.     

南阳膨胀土的工程地质特征和填筑适宜性

施工阶段的工程地质调查发现,宁（南京）西（西安）铁路内乡-镇平段南阳膨胀土成因类型上不仅有第四系冲积洪积粘土,而且发育上第三系湖相沉积粘土。不同成因的膨胀土具有不同的空间分布特征和工程性质,X射线衍射测试表明,南阳膨胀土的主要膨胀性粘土矿物是伊利石/蒙脱石混层矿物。物质组成和物理化学性质差异导致击实土在含水量变化条件下膨胀力和膨胀变形有明显的差别;对同一种膨胀土材料,其击实含水量越小,膨胀性越强,甚至含水量降低1 %～2 %,膨胀力就可以增加到200 %以上;击实膨胀土的直剪强度受到钙质结核含量的影响,对于膨胀势为高或强的膨胀土,结核含量小于15 % 时,经过干湿循环后直剪强度衰减量为40 %～65 %,结核含量为25 %～30 % 的强膨胀土直剪强度衰减量则低于30 %;对膨胀土的地质特征、工程性质、击实土的膨胀性和直剪试验结果进行分析,探讨其用于填筑铁路路基的适宜性,进行了填筑适宜性分级。依据研究成果制定的路基施工工艺取得了比较理想的工程效果     

蒸馏水中蒙脱石晶层间膨胀压力理论研究

蒙脱石颗粒周围的溶液浓度对其膨胀性有较大影响,传统的双电层模型可以对电解质环境下蒙脱石的膨胀特性做出较好的模拟,但并不适于蒸馏水的情况。针对膨润土在蒸馏水或纯水中已有的膨胀特性试验,本文在前人的研究基础上详细推导了蒸馏水中蒙脱石晶层间的膨胀压力模型,并给出一种简便算法。运用此算法可以避免非线性方程的求解,从而可以较方便的将膨胀力和晶层间距联系起来。     

压实红黏土的恒体积膨胀力与细观机制研究

针对目前量测土体膨胀力的主要方法所存在的不足,提出近似完全限制条件下测量土体膨胀力的改进方法。以压实红黏土为研究对象,测到不同初始状态（含水率、干密度）试样的膨胀力,并与膨胀反压法测得的膨胀力进行对比分析,发现限制膨胀方法测得的膨胀力要小于膨胀反压法的试验值。同时,显现出限制膨胀法测膨胀力具有3个主要优点：试验过程中保持土体不发生变形,更加符合膨胀力的物理定义;试验耗时少、占空间少;能测较宽含水率范围内的膨胀力。最后,利用压汞法和氮吸附法测得不同状态下土体的细观孔隙结构分布特征。结果表明：相同干密度试样,制样含水率对压实土体的孔隙分布影响显著;黏土晶间和粒间吸水自由膨胀后发生“不可逆”膨胀变形;土体发生“不可逆”膨胀变形程度是引起限制膨胀法和膨胀反压法所得试验结果出现差异的主要原因。     

Speciation,fractionation and plant availability of arsenic as induced by sorbents mixed with soil of Zarshuran (Iran)

The aim of this work was to investigate the effects of sorbent (natural and modified zeolite and bentonite, iron filings and ferric sulfate) on the speciation and bioavailability of arsenic in contaminated soil. The soil used in this experiment was collected from Zarshuran area (Western Azerbaijan province, NW Iran). The sorbents were added to the soil in various rates separately. After a month of incubation, sunflower was planted in pots. After harvest, soil and plant samples of each pot were analyzed. Then various species of arsenic were estimated in soil solutions by MINTEQ software program. Water-soluble arsenate, arsenite and exchangeable arsenic from each pot measured. The results showed that the sorbents had no effect on the speciation of arsenic. Mobility of arsenite in the soil solutions has not changed. Soils treated with natural bentonite and zeolite increased soluble arsenate concentration and decreased exchangeable arsenic concentration. Although Fe-zeolite increased soluble arsenate concentration, Fe-bentonite, iron filings and ferric sulfate decreased soluble arsenate concentration and exchangeable arsenic concentration. Finally, iron filings (containing 354 mmol Fe⁺³) vigorously increases in the plants biomass and decreases in the arsenic concentration in plants tissue, is suggested as the best sorbent for arsenic stabilization in the region.     

Suppression of swelling associated with ettringite formation in lime stabilized sulphate bearing clay soils by partial substitution of lime with ground granulated blastfurnace slag (GGBS)

Ettringite related swelling in lime-stabilized sulphate bearing clay soil systems has only been reported within the last decade although similar expansive behaviour has been reported in concrete over many years. The use of ground granulated blastfurnace slag (GGBS), an industrial by-product, is well established as a binder in many cement applications where it provides enhanced durability and high resistance to sulphate attack. This paper reports on efforts to extend the use of GGBS to highway and other foundation layers by determining the beneficial effect of the suppression of swelling of lime-stabilized clay soils, particularly in the presence of gypsum. The paper describes the results of laboratory tests on lime-stabilized kaolinite containing different levels of added gypsum and on lime-stabilized gypsum (selenite) bearing Kimmeridge Clay to which, in both cases, the lime has progressively been substituted with GGBS. The tests determine the linear expansion behaviour of compacted cylinders, during moist curing in a humid environment at 30°C and during subsequent soaking in de-ionized water. The results illustrate that substitution of lime with GGBS produces significant reduction in linear expansion of lime-stabilized clay soils particularly those containing gypsum.     

Geoenvironmental Testing

Geoenvironmental concerns involve unsaturated soils in problems like soil contamination, waste disposal and ground-atmosphere interactions. This paper deals with the two first points. To tackle geoenvironmental problems in unsaturated soils, it is necessary to identify experimentally the retention and transfer phenomena that govern the movements of fluids and chemical species in the unsaturated soil. Some of the experimental techniques used in unsaturated soils can be adapted to face these problems, but extensions accounting for the various physico-chemical processes involved in soil contamination and waste disposal are necessary, including temperature effects and the mechanical couplings resulting from the changes in temperature and chemical concentrations. After an introduction to the geoenvironmental problems that are related to unsaturated soils, the paper presents a series of experimental developments carried out in relation to retention and transfer properties of water (pure or with dissolved species), hydrocarbons and gas, also accounting for temperature effects and chemical effects. The techniques presented are applicable to soil contamination and waste disposal, with a special concern addressed to nuclear waste disposal, in which the effects of desaturation of the geological barrier together with the unsaturated nature of compacted engineered barriers appeared to be quite important.     

4A沸石分子筛对KNO3和NH4NO3的吸持作用

实验研究了4A沸石分子筛经熔融盐处理后对KNO₃和NH₄NO₃的吸持作用。结果表明：在实验条件下,KNO₃处理后的4A沸石中含钾(以K₂O计)15.01%,含NO^-₃ 9.23%;NH₄NO₃处理后的4A沸石中含NO^-₃ 10.78%,含NH⁺₄ 0.94%。熔融盐处理后的样品X射线衍射峰相对强度发生了变化,红外光谱中1 640 cm^-1附近水的吸收带强度减弱,1 390 cm^-1附近出现的NO^-₃离子的强吸收带及825 cm^-1附近出现的NO^-₃离子的弱吸收带,以及热重-差热曲线中KNO₃和NH₄NO₃的热失重和分解热效应均证明沸石中吸持盐的存在。处理后4A沸石分子筛的基本骨架结构没有被破坏,吸持盐的4A沸石对营养盐的储备大大提高,是潜在的缓释肥料。     

压实黏质砂土脱湿过程影响机制的核磁共振分析

通过对具有不同初始含水率和干密度的两种压实黏质砂土的脱湿曲线进行测试、分析和对比,并结合核磁共振技术,探讨了干密度、初始含水率和土样组分对压实黏质砂土脱湿过程的影响规律。利用核磁共振测得了试样在各级吸力下的T2时间（横向弛豫时间）分布曲线,定性地探讨了不同吸力下试样中的水分分布特征,揭示了干密度、初始含水率和土样组分对试样脱湿过程的微观机制影响。试验结果表明：干密度仅在低基质吸力条件下对试样脱湿过程产生重要影响,而在高吸力条件下初始含水率和试样组分起主导作用;核磁共振结果证实在压实黏质砂土中,小孔隙结构主要由初始含水率和试样组分控制,而大孔隙的结构主要取决于干密度;试样组分对压实土的内部结构和孔隙大小分布的影响比初始含水率大。     

Effect of Natural Zeolite and Cement Additive on the Strength of Sand

It is widely known and well emphasized that the cemented sand is one of economic and environmental topics in soil stabilization. In some instances, a blend of sand, cement and other materials such as fiber, glass, nano particle and zeolite can commercially be available and effectively used in soil stabilization especially in road construction. In regard to zeolite, its influence and effectiveness on the properties of cemented sands systems has not been completely explored. Hence, in this study, based on an experimental program, it has been tried to investigate the potential of a zeolite stabilizer known as additive material to improve the properties of cemented sands. A total number of 216 unconfined compression tests were carried out on cured samples in 7, 28 and 90 days. Results show unconfined compression strength and failure properties improvements of cement sand specimens when cement replaced by zeolite at optimum proportions of 30 % after 28 days due to pozzolanic reaction. The rate of strength improvement is approximately 20–78 and 20–60 % for 28 and 90 days curing times respectively. The efficiency of using zeolite has been enhanced by increasing the cement content and porosity of the compacted mixture. The replacement of cement by natural zeolite led to an increase of the pH after 14 days. Chemical oxygen demand (COD) tests demonstrate that the materials with the zeolite mixture reveal stronger adsorptive capacity of COD in compare to cemented mixture. Scanning electron microscope images show that adding zeolite in cemented sand changes the microstructure (filling large porosity and pozzolanic reaction) that results in increasing strength.