Seismic Slope Stability of Embankments Constructed with Pond Ash

Utilization of pond ash in large earthworks for geotechnical applications like construction of highway embankments, raising of ash dykes and filling low lying areas (construction fills), solves the waste disposal problem besides conserving the natural soils. However, design and construction of such geotechnical structures particularly in earthquake prone areas, requires thorough understanding of dynamic response of these structures under different seismic loading conditions. Here in this article, dynamic stability of embankments raised around the perimeter of ash ponds by the upstream and down stream methods of construction with coarse (ash from inflow point) and fine (ash from outflow point) pond ash materials, has been computed for different site specific earthquake scenarios appropriate for Delhi region. The performance of the embankments is analyzed using Quake/w and Slope/w software packages for steady-state seepage condition. The required dynamic properties of the materials are obtained form the various field and laboratory tests. The geotechnical structures constructed with ash exhibited similar type of response as that of with the natural soils. The performance of the structures is influenced by number factors such as type of construction (e.g. upstream or downstream), insitu conditions (e.g. stresses, density, phreatic line), and magnitude of dynamic loads, besides on the static and dynamic characteristics of the materials. The structures with the fine ash exhibit higher vulnerability to liquefaction related failures, which emphasizes need for carrying site-specific studies and adoption of proper construction measures to ensure design parameters.     

Strength characteristics of compacted pond ash

Strength properties of compacted ash layers depend to a great extent on the moulding conditions. This paper focuses on the effects of compaction energy and degree of saturation on strength characteristics of compacted pond ash. The pond ash sample, collected from the ash pond of Rourkela Steel Plant (RSP), was subjected to compactive energies varying from 357 kJ/m³ to 3488 kJ/m³. The optimum moisture content and maximum dry densities corresponding to different compactive energies were determined by conventional compaction tests. The shear strength parameters, unconfined compressive strengths (UCS) and California bearing ratio (CBR) values of specimens compacted to different dry densities and moisture content were assessed and reported. The effects of compaction energy and degree of saturation on shear strength parameters i.e. unit cohesion (c_u) and angle of internal friction (Ф) values and also the UCS values are evaluated and presented herein. The results indicate that the dry density and strength of the compacted pond ash can be suitably modified by controlling the compactive energy and moulding moisture content. The strength achieved in the present study is comparable to the good quality, similar graded conventional earth materials. Hence, it may be safely concluded that pond ash can replace the natural earth materials in geotechnical constructions.     

Shear strength characteristics of sand-mixed with granular rubber

Waste materials such as waste tires, rubbers, and plastic materials are normally produced in every society, entering the environment and causing serious problems. These problems may be somehow reduced by finding applications for them in engineering, for example, as lightweight materials for backfill in geotechnical projects. To this aim, this paper demonstrates how shear strength characteristics of sand mixed with various percentages of waste garden hose grains are altered. A relatively, uniform sand has been mixed with waste hose grains in loose and slightly compacted states. Waste hose grains were prepared with special popular machinery in a local area. Various sand-rubber mixtures having 0%, 10%, 15%, 20%, 50%, 70%, and 100% waste hose particles by weight were chosen. The rubber grains were distributed in the sand such that uniform mixtures are obtained. In order to compare the shear strength of different sand-rubber samples, two compaction states were considered. The results show that the influencing parameters on shear strength characteristics of sand-rubber mixtures are normal stress, mixture unit weight, and rubber content. With the selected waste hose particles, compaction states, and rubber contents, the initial friction angle φ₁ does not change significantly. However, an apparent cohesion appears in the mixtures. From environmental point of view and due to lightweight material for the sand-waste hose particles, it may be useful to use such materials in corresponding geotechnical projects. This revised version was published online in July 2006 with corrections to the Cover Date.     

One-Dimensional Consolidation of Sedimented Stowed Pond Ash

Use of fly ash locked in the ash ponds in geotechnical applications such as stowing or backfilling of the mines is an attractive alternative to solve the disposal problem. Before it is used as a stowing or backfilling material, the response of the fly ash?to imposed load must be determined in order to assess its load taking ability. The present study examines the effect of time and incremental load on the consolidation characteristics of the sedimented stowed pond ash using a fixed ring consolidometer. The important parameters, viz. rate of settlement, consolidation coefficients and void ratio, etc. of the hydraulically stowed pond ash collected after 7, 14, 21, 28 and 35?days of stowing under step incremental loads are determined. The study revealed that 60.42–84.87% settlement of the sedimented stowed pond ash takes place in the initial 1?min of the loading. In addition, it is observed that the coefficient of consolidation of the sedimented stowed pond ash, which varies in the range of 0.0195–0.1882?cm²/min, is comparatively low and decreases with the increment of applied load and time. This indicates that the structures lying above the stowed pond ash mass will undergo gradual settling and not suffer large deformation.     

Stabilization of desert sands using municipal solid waste incinerator ash

This paper presents experimental results on the use of incinerator ash in stabilizing desert sands for possible use in geotechnical engineering applications. The incinerator ash was added in percentages of 2, 4, 8, 10 and 12%, by dry weight of sand. Laboratory tests such as compaction, unconfined compression, shear box and hydraulic conductivity were performed to measure the engineering characteristics of the stabilized material. The results showed substantial improvements in unconfined compressive strength and shear strength parameters (c and φ). Thus, incinerator ash can be used to improve the shear strength characteristics of desert sands. The permeability of the sand–incinerator ash mixture was relatively low.     

广西红粘土击实样强度特性与胀缩性能

通过对广西贵港红粘土重型击实样的室内试验研究,探讨了其力学特性、胀缩性能、孔径分布特征与含水量之间的关系。结果表明：干密度指标总体上能反映红粘土击实样的强度规律,但非饱和击实样强度峰值对应的含水量因基质吸力作用而偏小,饱和后土体由于吸水膨胀与基质吸力的消失,使得强度峰值对应含水量较饱和前明显增大,红粘土在最优含水量下压实,虽可获得很高的压实度,但饱和后的强度并非最大;红粘土击实样的胀缩性能主要由含水量决定,同时,受到干密度的影响;孔隙主要以孔径在0.01～0.05μm范围内的小孔隙为主,为进一步掌握红粘土的工程力学特性提供了帮助。     

The Los Chocoyos Ash, guatemala: A major stratigraphic marker in middle America and in three ocean basins

The Los Chocoyos Ash, having erupted from vents near the Lake Atitlán caldera, Guatemala, is perhaps the largest Quaternary silicic pyroclastic unit in Central America. It consists of an underlying H-tephra member and an overlying ash-flow member. One-hundred-and-five samples of ash from the Guatemalan Highlands and deep-sea cores in the equatorial Pacific and Gulf of Mexico were analyzed by neutron activation and/or electron microprobe. Glass shard chemistry, determined by microprobe, is useful for distinguishing several very widespread, distinct, deep-sea ash layers, but needs support from trace-element data when applied on land to distinguish between many individual eruptions from the same province. Data from this study support the correlation of the Worzel ‘D’ layer and the Los Chocoyos Ash proposed by Hahn et al. (1979) and Bowles et al. (1973). Chemical data from this study are used to correlate the Y-8 ash layer of the Gulf of Mexico with the Los Chocoyos Ash. The recognition of the Los Chocoyos Ash in the Gulf of Mexico and equatorial Pacific increases the known areal extent of the unit to more than 6 × 10⁶ km² and allows an age of 84,000 yr B.P. to be assigned to the formation on the basis of oxygen-isotope stratigraphy, biostratigraphy, and Pa-Th-isotope data. Trace-element data obtained from seven other ash layers in the Gulf of Mexico and the equatorial Pacific, when combined with new land-based data, should allow further correlation and dating of ash units in Central America.     

Settlement of compacted ash fills

The coal ash is a by-product of coal-fired thermal power station. It is extensively used as a geo-material for landfill. The compacted ash is used as a structural fill if it is properly characterized for load-bearing capacity and settlement. The main objective of the present work is to characterize ash material and to evaluate its settlement characteristics. The ash is normally compacted by vibration at or near optimum moisture for its performance as structural fill. The overt characteristics of ashes are viewed similar to cohesionless soils. However, the mass behavior may have differences due to the subtle influence of chemical and physical processes involved in its formation. The empirical and analytical methods predicting settlement of footing under static loading require direct or indirect measurement of density and stress state in the deposit. In the present work, experimental investigations for settlement prediction were carried out on compacted coal ash produced at Ropar thermal power station in India, which was conveniently classified as ASTM class F ash. The settlement was experimentally obtained for the rigid plates having least dimension more than 0.3 m on ashes compacted at varying degree of compaction. The predicted settlement based on the observed data of coal ash using conventional techniques for soils was found to be conservative. A relationship between settlement and foundation size is proposed at varying compaction to obtain the settlement of compacted ash. At a higher degree of compaction, the settlement of a foundation may not exceed the allowable settlements in the working stress range.     

Environmental geological and geotechnical investigations related to the potential use of Ankara clay as a compacted landfill liner material, Turkey

Clay-bearing Upper Pliocene red clastics and Quaternary alluvial deposits occupy the Ankara basin. The clayey levels of the Upper Pliocene deposits, referred to as Ankara clay, is considered as a source for compacted clay liners due to their low coefficients of permeability and widespread distributions throughout Ankara. This study investigates the geological, geotechnical and mineralogical properties of the founding clayey soils at two sites of the Ankara region. The geotechnical index properties along with the hydraulic conductivities of the clayey soil samples collected from these sites were determined. A mathematical relation between the clay mineralogical content and hydraulic conductivity was established. The results of this investigation show that, from a geotechnical point of view, Ankara clay may be regarded as a highly suitable material for a compacted clay landfill liner given that its mineralogical compatibility with leachate is confirmed.     

Geostatistical analysis of field hydraulic conductivity in compacted clay

Hydraulic conductivity(K) of fractured or porous materials is associated intimately with water flow and chemical transport. Basic concepts imply uniform flux through a homogeneous cross-sectional area. If flow were to occur only through part of the area, actual rates could be considerably different. Because laboratory values ofK in compacted clays seldom agree with field estimates, questions arise as to what the true values ofK are and how they should be estimated. Hydraulic conductivity values were measured on a 10×25 m elevated bridge-like platform. A constant water level was maintained for 1 yr over a 0.3-m thick layer of compacted clay, and inflow and outflow rates were monitored using 10×25 grids of 0.3-m diameter infiltration rings and outflow drains subtending approximately 1×1 m blocks of compacted clay. Variography of inflow and outflow data established relationships between cores and blocks of clay, respectively. Because distributions of outflow rates were much less and bore little resemblance to the distributions of break-through rates based on tracer studies, presence of macropores and preferential flow through the macropores was suspected. Subsequently, probability kriging was applied to reevaluate distribution of flux rates and possible location of macropores. Sites exceeding a threshold outflow of 100×10^–9 m/s were classified as outliers and were assumed to probably contain a significant population of macropores. Different sampling schemes were examined. Variogram analysis of outflows with and without outliers suggested adequacy of sampling the site at 50 randomly chosen locations. Because of the potential contribution of macropores to pollutant transport and the practical necessity of extrapolating small plot values to larger areas, conditional simulations with and without outliers were carried out. Simulated scenarios based on all available data compared well with conditional simulations based on randomly chosen locations.This paper was presented at MGUS 87 Conference, Redwood City, California, 14 April 1987.     

Geotechnical Properties of Low Calcium and High Calcium Fly Ash

In this paper, a comparative study has been made for physical and engineering properties of low calcium and high calcium Indian fly ash. The grain size distribution of fly ash is independent of lime content. Fly ash particles of size >75 μm are mostly irregular in shape whereas finer fractions are spherical for low calcium fly ash. For high calcium fly ash, chemical and mineralogical differences have been observed for different size fractions. Compared to low calcium fly ash, optimum moisture content is low and maximum dry density is high for high calcium fly ash. Optimum moisture content is directly proportional and maximum dry density is inversely proportional to the carbon content. The mode and duration of curing have significant effect on strength and stress–strain behavior of compacted fly ash. The gain in strength with time for high calcium fly ash is very high compared to that of low calcium fly ash due to presence of reactive minerals and glassy phase.     

压实花岗岩风化土物理力学性状试验研究

吕梁山脉东麓花岗岩风化土的工程类型与我国南方以及日本、韩国等地的花岗岩风化土有较大差别。为了对吕梁山压实花岗岩风化土的物理力学性状有较全面认识,通过常规土工试验、X射线衍射试验、大固结试验、大三轴试验等方法,对其击实特性、承载特性、变形特性、剪胀特性、强度特性等进行了分析。结果表明：黏土掺量对花岗岩风化土的击实特性和承载特性影响较大,存在两个不同的黏土掺量界限值（约8%和4%）,分别使得试样密实状态和承载能力处于最优;试样不存在膨胀潜势,无膨胀性,为低压缩性材料;压实花岗岩风化土颗粒破碎的特点导致试样二次加载→卸载压缩曲线存在两次明显塑性变形增大的现象;剪切时由于试样内部颗粒历经压密→错动→翻越→破碎的过程,导致不同围压下试样表现出不同的剪胀性;剪切过程中由于颗粒破碎的存在,使得试样表现出强度非线性特点。     

Stabilization of fuel oil contaminated soil—A case study

Fuel oil contamination brings adverse effect on basic geotechnical properties of foundation soil. The present study pertains to one such case, from the petrochemical complex near Vadodara City in Gujarat State, India. Here, the fuel oil contaminated soil samples exhibit drastic changes in their geotechnical parameters. Noteworthy among such deleterious changes are: decrease in maximum dry density (–4%), cohesion (–66%), angle of internal friction (–23%) and unconfined compressive strength (UCS) (–35%) and increase in liquid limit (+11%). An attempt has been made to stabilize the contaminated soil using various additives viz., lime, fly ash and cement independently as well as an admixture of different combinations. It is apparent from the test results that the stabilization agents improved the geo-technical properties of the soil by way of cation exchange, agglomeration, and pozzuolanic actions. The best results were observed when a combination of 10% lime, 5% fly ash and 5% cement was added to the contaminated soil. The improvement in unconfined compressive strength (UCS), cohesion and angle of internal friction can be attributed to neo-formations such as Calcium Silicate Hydrates (CSH, CSH-1) that coats and binds the soil particles. Formation of stable complex between oil and metallic cations, results in reduction of leachableoil.     

Geotechnical Characteristics of Volcanic Soils Taken from Recent Eruptions

Recent volcanic eruptions at Mt. Unzen (Japan) in 1990 and Mt. Pinatubo (Philippines) in 1991 produced voluminous amounts of ash and sediments which inundated widespread areas. In later rehabilitation and reconstruction, it is practical and economical to use these freshly deposited sediments as materials for foundations and embankments. However, the geotechnical properties of young volcanic products have not been fully investigated. Accordingly, we investigated the geotechnical characteristics of volcanic soils associated with three recent eruptions, namely, the Unzen and Izu-Oshima eruptions of 1990 and 1986, respectively, in Japan and the Pinatubo eruption of 1991 in the Philippines. We specifically investigated index properties, permeability and compaction characteristics, and strength and deformation behavior in drained conditions. Additionally, we examined the dynamic properties and liquefaction characteristics of samples taken from Mt. Pinatubo. The results showed that the geotechnical characteristics of the deposits generally varied with the sampling sites. Depending on the location, either upstream or downstream from a volcano, the preferential sizing due to alluvial deposition affects engineering properties of the deposits. For example, volcanic sediments upstream from Mt. Pinatubo have high compressibility and low cyclic strength, whereas those taken downstream show dilative tendencies and high liquefaction strength.     

Magnetic susceptibility as a proxy for coal ash pollution within riverbed sediments in a watershed with complex geology (southeastern USA)

A study of near surface sediments from the Dan River (southeastern USA) was conducted to assess the use of magnetic properties as proxies of coal ash after a recent spill. The watershed geology is diverse and potentially contributes magnetic minerals to riverbed sediment from diabase dikes in the Dan River Triassic Basin and from granitic gneiss outside the basin. Coal ash is heterogeneous, including aluminosilicate spheres, amorphous particles and carbonaceous rods and lacy particles. The magnetic fraction of ash from the failed storage pond is up to 17 wt% and is mostly composed of black spheres with maghemite and magnetite. Ash was detected in riverbed sediment from quiet water settings such as inside of meander bends, the confluence of tributary streams and near islands between the spill site and 20 miles downstream in the Schoolfield Reservoir, Danville, VA. The strong magnetic signal is detected above background in riverbed samples and is strongly positively correlated with total ash; elevated low field magnetic susceptibility (χ _LF) is evident in samples with ≥ 12% ash content. Anhysteretic remanent magnetization and hysteresis parameters delineate native sediment, ash-bearing sediment, and diabase dikes. Between 20 and 70 miles downstream of the spill site, ash concentrations were either buried or too low due to dilution with native sediment to be detected with χ _LF in riverbed samples.     

非饱和击实粉土的强度和屈服特性研究

由于吸力量测技术的困难,对京―九线粉土在不同含水率下击实并进行三轴不排水剪切试验,研究其强度和屈服特性,为非饱和击实粉土力学模型的建立提供依据。试验结果表明：该击实粉土在剪切过程中,在最优含水率干侧击实的土样具有较高的强度,应力-应变关系曲线呈软化趋势,土样先剪缩后剪胀,湿侧击实的土样具有较低的强度,应力-应变关系曲线呈硬化趋势,土样不断剪缩;随着试样击实含水率的增加,击实粉土的强度和屈服应力不断减小,水对土体具有一定的软化作用;不同击实含水率下,土样在q-p平面内破坏时的屈服轨迹为近似平行的斜直线,含水率对临界状态线的斜率没有影响;含水率对击实粉土抗剪强度的贡献表现为土体的似黏聚力的增加,似黏聚力与含水率之间呈乘幂关系,得出以含水率为变量的击实粉土强度计算公式,可在实际工程中推广应用。     

鄂尔多斯盆地东胜-神木地区侏罗系煤中常量元素地球化学特征

对鄂尔多斯盆地东胜-神木地区侏罗系直罗组和延安组的9个煤样进行了工业分析和元素分析以及煤灰常量元素测试分析,探讨了成煤环境条件对煤样性质的影响,并揭示了不同聚煤体系煤灰中常量元素的特征及其控制因素.分析测试结果显示,直罗组和延安组不同聚煤体系中煤的灰分产率、矿物含量和有机C含量呈现明显的变化趋势,从延安组Ⅱ、Ⅲ、Ⅳ单元...     

Behaviour of model footing on pond ash

This paper focuses on the effective utilization of pond ash, as foundation medium. A series of laboratory model tests have been carried out using square, rectangular and strip footings on pond ash. The effects of dry density, degree of saturation of pond ash, size and shape of footing on ultimate bearing capacity of shallow foundations are presented in this paper. Local shear failure of a square footing on pond ash at 37% moisture content (optimum moisture content) is observed up to the values of dry density 11.20 kN/m³ and general shear failure takes place at the values of dry density 11.48 kN/m³ and 11.70 kN/m³. Effects of degree of saturation on ultimate bearing capacity were studied. Experimental results show that degree of saturation significantly affects the ultimate bearing capacity of strip footing. The effect of footing length to width ratio (L/B), on increase in ultimate bearing capacity of pond ash, is insignificant for L/B ≥ 10 in case of rectangular footings. The effects of size of footing on ultimate bearing capacity for all shapes of footings viz., square, rectangular and strip footings are highlighted.     

Utilization of bituminous limestone ash from EL-LAJJUN area for engineering applications

The following work aims at minimizing the environmental impact of the solid wastes (ash) that is produced after the utilization of the bituminous limestone in thermal power stations and /or retort processes. Limy ash has been prepared from the El-Lajjun bituminous limestone by direct combustion at 1,200, 950, and 525°C respectively. The laboratory tests have been selected with respect to construction needs and possible post construction conditions. Utilization of the various types of ash in the stabilization problematic soils from Jordan as brown soils and the clayey marl has revealed optimum results. The unconfined compressive strength of the parent brown soil and the clayey marl has been raised from 5 kg/cm² to 50 and 25 kg/cm², respectively. The CBR value has been raised from 4.5 to 150% for both problematic soil types. Various mortars and construction elements can be produced at normal room curing temperature without the use of ordinary Portland cement (OPC). Low quality sub-base and base course can be mixed with ash to produce cement treated base (CTB) and roller compacted concrete (RCC) without OPC. Durable pavements, embankments can be constructed with very long life and low cost. CTB and RCC utilizing ash can be used in dam construction instead of normal soil in earth fill dams. The high alkalinity of El-Lajjun ash is considered as a disadvantage to be utilized in normal concrete mixes for structural purposes. Ash only can be mixed with aggregates to produce lean concrete like for blinding purposes to be prepared for foundation activities.     

尾矿库排渗工程技术方法

为消除或减少尾矿库的安全风险,重要措施就是降低尾矿库坝体内的浸润线,而排渗工程技术方法是其主要手段。本文结合部分岩土工程技术在尾矿库排渗工程中的运用,并通过多项工程实践,系统讨论与总结尾矿库排渗工程技术方法中的盲沟排渗法、水平孔排渗法、辐射井排渗法、井点管抽水法、其它联合排渗措施的原理特点、施工方法与质量控制要点。