Chemo–mechanical interactions in clay: a correlation between clay mineralogy and Atterberg limits

Among some few others tests, the evaluation of the Atterberg limits is a very basic soil mechanical test allowing a first insight into the chemical reactivity of clays. Basically, the liquid limit and the plasticity index are highly and mainly influenced by the ability of clay minerals to interact with liquids. In this contribution, a correlation between the Atterberg limits and clay mineralogy is proposed. This correlation increases the understanding between clay mineralogists and engineers in soil mechanics; additionally a wealth of information in clay mineralogy literature is now available to predict the mechanical behaviour of clays via index tests.     

Physico-chemical effects on clay due to electromigration using stainless steel electrodes

The physico-chemical changes in clay soils due to the application of electrokinetics are difficult to predict with accuracy because of the very wide range of parameters interacting. The effects of the application of an electrical gradient across controlled specimens of a pure form of kaolinite using stainless steel electrodes and a deionised water feed to the electrodes, to mimic electrokinetic stabilisation without the stabiliser added, are reported. The specimens in which electrical and chemical changes were induced over different time periods (3, 7, 14 and 28 days) were subsequently tested for Atterberg limits, undrained shear strength, water content, pH, conductivity, Fe concentration and zeta potential. Changes in strength and plasticity indices were attributed to electrolysis, electro-osmosis, electrode degradation, clay mineral dissolution, ion movement due to electromigration, cation exchange reactions and precipitation of reaction products.     

The effect of self-healing process on the strength increase in clay

In this study, the effect of an additive with nano-montmorillonite brand on the process of self-healing on clay soil was considered. Laboratory tests include Atterberg limits and unpressurized compressive strength on the natural soil and soil samples contain different weight percentages of the additive. The results reveal that the addition of the additive up to 5% of the soil dry weight led to significant changes in the physical and mechanical properties of improved soil such as increasing plasticity index, increasing compressive strength and consequently, increasing the self-healing on clay soil. These changes are functions of the weight percent of the additive and the age of the samples. Moreover, laboratory results were investigated by SEM and FESEM images. Data was collected from uniaxial test and Scanning Electron Microscope images indicate that the maximum amount of self-healing occurred in the samples with 5% nano-clay on the sixtieth day after the initial failure.     

Effects of organic matter on the physical and the physicochemical properties of an illitic soil

The main thrust of this study is to investigate the effects of organic matter on the physical and the physicochemical properties of illitic soils. For this purpose, organic matter (peat) was added to inorganic illitic clayey soil at eight levels (0%, 5%, 10%, 12.5%, 15%, 17.5%, 20%, and 30% by weight). The physicochemical properties of the resulting soils were determined using a Grain Size Analyzer (GSA) with specific surface area measurement, Scanning Electron Microscopy (SEM), and Infrared Spectroscopy (IR). The physical properties of the mixtures were determined by conducting a series of laboratory tests including Atterberg limits, compaction, unconfined compressive strength, and swell characteristics tests. The results showed that at low organic contents (in general less than 15%) the soil particles tend to aggregate, whereas at higher organic contents the soil particles tend to disperse. Also, the IR tests showed that direct chemical interactions took place between the organic and the inorganic fractions of the mixtures. The tests on the physical properties showed that at low organic content (up to 10%) the plasticity index slightly increased then after, the plasticity index decreased with increasing organic content. Organic matter has shown to decrease the maximum dry density and increase the optimum water content, nevertheless, although organic matter decreased the soil's compactability, the feasibility of compaction of slightly organic content soils still exists. Moreover, it was shown that organic matter decreased the peak strength values and increased the water contents at these peak strengths. The final free swell for illitic soils increased with increasing levels of added organic matter.     

Swell potential and shear strength estimation of clays

This paper deals with the indirect estimation of the two main parameters of cohesive soils (swell percent and shear strength) that play an important role in the deformation of structures. While the literature contains several empirical techniques for assessing the swelling potential and shear strength, no satisfactory equations are available that provide an estimation of percent swell and shear strength based on liquidity index. In this study clayey soil samples were collected from five alluvial deposits in Turkey and parameters were determined including liquidity index, percent swell and shear strength. Regression equations established for the liquidity index–percent swell and liquidity index–undrained shear strength had high correlation coefficients of 0.87 and 0.95 respectively. It must be considered that the equations proposed in this paper were obtained from the soils having very low organic material and ~ 50% clay mineral content, a liquidity index range of − 0.52–0.91. For wider and generalized application of the equations, the formulae would have to be tested over a data set with a larger range of liquidty index, organic material and clay content. However, the equations, derived from the samples used in this study, apply well with an acceptable accuracy to be used for percent swell and undrained shear strength estimations at the preliminary stage of site investigations.     

Impact of diatoms on fabric and chemical stability of diatom–kaolin mixtures

Natural soils containing diatoms tend to have high compressibility, low shear strength, and difficulty of compaction. Yet, given their unique characteristics (i.e., high water absorption, liquid limit, and friction angle), there is great potential for utilizing diatoms and natural diatomaceous soils in the development of engineered particulate materials for geotechnical and geoenvironmental engineering applications. One of these applications is the use of diatom-modified soils for the construction of chemical and hydraulically-stable landfill liners and covers. Two important considerations for the long term response of liners and covers are the stability against: (1) ionic concentration-induced aggregation and (2) capillary force-induced deformations that may cause crack formation. In this study, we investigate the influence of diatomaceous earth on the resulting soil fabric and chemical stability through fabric formation studies, changes in water retention characteristics, and silica dissolution of diatomaceous earth–kaolin mixtures. Testing includes bench-scale fabric formation tests (i.e., Atterberg limits, sedimentation, and viscosity) and the measurement of water retention curves for various diatom–kaolin mixtures. The presence of diatoms (1) decreased the tendency of the mineral mixture to coagulate in the presence of salt, (2) significantly increased the liquid and plastic limits of the mineral mixture, (3) increased the water holding capacity of the mineral mixtures, and (4) reduced the solubility of kaolin mixtures, even in electrolyte solutions. That is, the presence of the diatoms has a great impact on the overall behavior of the soil mixtures by reducing the influence of pore fluid ionic concentration and by creating a stiffer skeleton that reduces the soil tendencies to deform due to osmotic and matric suction changes.     

A dimensional description of the unconfined compressive strength of artificially cemented fine-grained soils

Abstract

This study aims at establishing a universal predictive model for the unconfined compressive strength (UCS) of artificially cemented fine-grained soils. Model development, its validation and calibration were carried out using a comprehensive database gathered from the research literature. The dimensional analysis concept was successfully extended to the soil–cement UCS problem, thereby leading to a practical dimensional model capable of simulating the UCS as a function of the blend’s index properties — that is, cement content, specific surface area, curing time, and the compaction state parameters (including water content and dry density). The predictive capability of the proposed model was examined and further validated using routine statistical tests, as well as conventional fit-measure indices which resulted in R²?>?0.95 and NRMSE < 5%. A sensitivity analysis was also carried out to quantify the relative impacts of cement content, curing time and soil plasticity on the UCS. The higher the soil plasticity, the higher the positive sensitivity to cement content, implying that soils of higher plasticity would require higher cement contents for stabilization. On the contrary, the higher the soil plasticity, the lower the positive sensitivity to curing time, indicating a more effective cement hydration in soils of lower plasticity. Finally, an explicit calibration procedure, involving a total of three UCS measurements for three recommended soil–cement mix designs, was proposed and validated, thus allowing for the proposed model to be implemented with confidence for predictive purposes, preliminary design assessments and/or soil–cement optimization studies.     

Reduction of the shrinkage–swelling potential with polymer nanocomposite stabilization

This article describes the application of using polymer stabilization to create a new hydrophobic (nanocomposite) material with swollen clay. A series of tests were performed with different polymer contents to study the effect of using polypropylene as a partial soil stabilizer and a shrinkage–swelling modifier for expansive soils. The effect of the obtained clay–polymer nanocomposites on the shear strength of swelling soils was also investigated. The tests showed that the resulting nanocomposites acted as nanofiller materials and decreased both the plasticity index and permeability. The optimum moisture content and dry density decreased relatively with increasing polymer content. The polymer inclusions significantly reduced the free swelling and swelling pressure values. In addition, the produced nanocomposites reduced the volumetric shrinkage of the expansive soils and created isotropic and compressible materials. The unconfined compressive strength of the soil increased significantly with increasing polymer content. The proposed stabilized technique increased the bearing capacity under the model footing and modified the stress settlement relationship. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A Generalized Relationship for Determination of Tensile Strength of Fine-Grained Soils from Shrinkage Characteristics

Tensile strength of fine-grained soils has been extensively investigated by earlier researchers and several methodologies have been evolved for its determination. However, either most of these methods are not valid/applicable for a wide range of moisture contents or they involve tedious sample/specimen preparation. In this context, the methodology of determining tensile strength by employing thin films, which is available in the literature, has been found to be quite handy and useful. It has been observed that a unique relationship exists among the tensile strength, moisture content, and shrinkage characteristics of fine-grained soils. This methodology is appreciable due to its applicability to a wide range of moisture contents, comparable ease of sample preparation and testing, and the obtained results lack generalization. Exhaustive tests were conducted on fine-grained soils of entirely different characteristics and generalized relationships have been proposed between the percentage linear shrinkage, tensile strength, and moisture content (defined as liquid to solid ratio). Based on a critical analysis of the results available in the literature, the efficiency of such relationships for determination of tensile strength of fine-grained soils has been demonstrated. In the authors’ opinion, such relationships would be quite useful for determining tensile strength of fine-grained soils from their linear shrinkage, which can easily be measured in a conventional geotechnical engineering laboratory.     

Injection of saline solutions to improve the electro-osmotic pressure and consolidation of foundation soil

Injection of saline solutions can enhance the effect of electro-osmotic pressure. This study considers the consolidation and stability of foundation soil for building construction. Kaolinite (KGa-1) and Taipei silty clay were subjected to zeta potential (ZP), electro-osmosis and laboratory vane shear tests with injection of saline solutions. The ZP values decrease (i.e., less negative potential) with increased cationic valences and concentrations. The increased electro-osmotic permeability from injecting CaCl₂ (1 N, EOC5) solution is about 172% higher than that without injection due to an increase of drained water from the cathode and the resulting increase of undrained shear strength. Average undrained shear strength for injecting CaCl₂ solution over a period of 7 days is about 4 to 5 times greater than that without injection during electro-osmosis tests. Electro-osmosis tests with injection of saline solutions reveal that the increase of undrained soil shear strength (ΔS_u) is proportional to the ZP tests.     

Influence of heavy metal contaminants at variable pH regimes on rheological behaviour of bentonite

Long-term competent performances of clays as barrier and liner systems for waste landfills are dependent on both the physico-mechanical properties and attenuation characteristics of the clay soils. The presence of heavy metal ions in the pore water will alter the physico-chemical characteristics of the clay–water system, resulting in changes in the short- and long-term mechanical and chemical behaviour of the clay soil barrier materials. This study investigates bentonite–contaminant interaction at different pH levels and heavy metal ion concentrations, and their resultant effect on the mechanical behaviour of bentonite soil. A set of physico-chemical experiments including Atterberg limits, precipitation testing, pH measurement and consolidation were performed to investigate the fundamental mechanism of soil–contaminant interaction from a rheological point of view. Consolidation tests were performed to study volume change behaviour with respect to the control exercised by mechanical and osmotic stresses. The impact of multiple aspects of heavy metal ion interaction on the osmotic compressibility and consolidation of bentonite is investigated. It is shown that while the selectivity phenomenon governs the adsorption characteristics of contaminated bentonite, the microstructural change due to the lower pH level and the high concentration of HMs, the different onset of precipitation for Zn and Pb, and the osmotic phenomenon control the rheological performance of compacted bentonite. The theoretical aspect of the experimental investigation is addressed and the restrictions of classical double layer theory for heavy metal/clay soils interaction are illustrated.     

The effect of the exchangeable cations on the physico-chemical properties of Wyoming bentonites

A series of Wyoming bentonites of differing surface chemistry were tested for various mechanical properties, including rheology, Atterberg limits, and their suitability as soil sealants.The results suggest that a bentonite with a sodium vs. calcium and magnesium ratio of 60:20:20% will perform better than others with different ratios.While other factors do influence the industrial performance of bentonites, this ratio is of major importance for most applications. In the foundry industry different criteria apply.     

Application of the Taguchi Method in Establishing Criticality of Parameters that Influence Cracking Characteristics of Fine-Grained Soils

Extensive studies have been conducted by earlier researchers to understand cracking characteristics of fine-grained soils. Based on these studies, several theories and models which facilitate understanding the effect of various soil- and environment-specific parameters (viz., clay content, plasticity, free swelling index, specimen dimensions, boundary conditions, temperature, and humidity) that influence cracking characteristics of such soils have been proposed. A critical synthesis of the existing literature reveals that selection of any crack sealing/arresting technique would largely depend on the most critical of these parameters. However, studies related to identification of this critical parameter(s) and its (their) influence on cracking characteristics of fine-grained soils are not available in the existing literature. Hence, efforts have been made in the present study to establish the effect of each of these parameters on the cracking characteristics of fine-grained soils and the most critical parameter(s) has/have been identified. To achieve this, the Taguchi method, which is basically a statistical method and has been widely adopted for designing experiments and optimizing and/or detecting the most influential parameter(s) from the set of parameters of any multi-variant problem, has been employed. From the present study, it has been demonstrated that temperature, humidity, and mineralogy are the most critical parameters that affect cracking behavior of fine-grained soils.     

Flow of a Newtonian fluid and a yield stress fluid around a plate inclined at 45° in interaction with a wall

This experimental and numerical study focuses on the determination of drag and lifts forces acting on inclined plate at 45° placed near a wall in a uniform flow of Newtonian and yield stress fluid. The inertia of the fluid is considered negligible. The influences of yield stress, shear thinning, and the distance between the plate and the wall were examined precisely. It is shown that the drag and lift coefficients decrease as the Oldroyd number increases and increase as the gap decreases. The unyielded zones around the plate were also determined. Their surfaces increase with the Oldroyd number. When the yield stress is low, the decrease of the shear thinning index n tends to decrease these unyielded zones. For the experimental part, a Carbopol gel was used as a fluid model. Experimental measurements were compared with numerical and published results, particularly in the plasticity context developed for soil mechanics. Differences are discussed in terms of the influence of elasticity and plasticity.     

水泥/玄武岩纤维复合固化剂分别对泥炭质土静力特性的影响

为了研究单掺水泥及复合固化剂(由水泥、生玄武岩纤维、石灰和生石膏组成)对滇池地区高原湖相泥炭质土静力特性的影响,对不同掺量水平下的水泥改良土和复合固化剂改良土进行静三轴不固结不排水剪切试验,研究了两种改良土的三轴应力应变关系与抗剪强度变化规律。研究表明:随掺量的增加,两种改良土的主应力差峰值强度增大;当掺入复合固化剂的质量分数为15%时,相比5%、10%两个掺量水平,复合固化剂改良土的三轴应力应变关系由“应变硬化型”转变为“应变软化型”,且抗剪强度显著提升;当改良土的内部结构发生破坏时,水泥改良土的抗剪强度有较大损失,而复合固化剂改良土仍保持较高的抗剪强度。     

季冻区粉煤灰加固路基土力学性能试验研究

为探究冻融循环作用对粉煤灰加固路基土力学性能影响,对冻融循环次数、含水率、粉煤灰掺量不同的盐渍土开展无侧限抗压试验和三轴剪切试验,研究冻融循环后土体的应力-应变曲线、无侧限抗压强度、黏聚力和内摩擦角的变化情况。使用Design-Expert 8.0软件,研究冻融循环次数、粉煤灰掺量、含水率及各因素交互作用对盐渍土力学性质影响的显著性程度。结果表明:多次冻融循环后,盐渍土无侧限抗压强度、黏聚力和内摩擦角均有下降,经历1~7次冻融循环时,土体各力学参数下降速率较快;随着粉煤灰掺量的增加,盐渍土的内摩擦角、黏聚力、无侧限抗压强度和抗剪强度呈现出先升高后下降的变化趋势。基于显著性分析理论,冻融循环次数与含水率的交互作用对盐渍土无侧限抗压强度和黏聚力的影响较为显著,粉煤灰掺量与冻融循环次数的交互作用仅对无侧限抗压强度影响较为显著。为提高路基土强度及抗冻融的能力,加快粉煤灰综合利用进度,根据软件和公式模拟结果,推荐在路基土中依据质量比掺加15%粉煤灰,并将经历7次冻融循环后压实盐渍土的力学指标作为工程设计参考值。     

Investigation on Cracking Characteristics of Fine-Grained Soils Under Varied Environmental Conditions

Several theories and models that define cracking characteristics of fine-grained soils have been proposed by earlier researchers. However, it has been realized that cracking characteristics of these soils are mainly influenced by the environmental conditions to which they are exposed and on their mineralogical composition. To demonstrate this, investigations were conducted on soils of entirely different characteristics and their cracking characteristics, under varied environmental conditions, resorting to “image analysis.” Based on the study, it has been observed that the cracking characteristics of fine-grained soils, defined as a function of evaporation rate, depend on the soil type (i.e., its mineralogy), environmental conditions, and the thickness of the specimen.     

Shearing behaviour of slightly compressed cohesive granular materials

In order to describe the failure properties of slightly compressed cohesive granular materials, the yield criteria must be known. Yield criteria from plasticity theory and soil mechanics are discussed with respect to their applicability to granular materials in powder technology. Shear tests are used to measure the failure properties. The shear behaviour in the flow factor tester or Jenike and in a modified version of the simple shear apparatus of Roscoe will be described. Test results from measurements with both apparatuses will be compared and it will be shown how the different results influence the design of hoppers.     

The effect of allophane on soil properties

Allophane is a widely distributed clay mineral. Although characteristic of soils derived from volcanic ash, it has also been identified in Podzols and podzolised soils. Certain distinctive characteristics can be attributed to the spherical shape of allophane. The apparent specific surface is high and is decreased markedly on drying, thus enabling the external and internal surface areas and hence diameters of the spherules to be calculated. High phosphate retention is characteristics. Equations are presented showing that for allophanic soils there is a weaker correlation of phosphate retention with aluminum soluble in Tamm's solution than in non-allophanic soils. This is believed to be due to the dissolution of aluminum in hydrous oxides, organic complexes, as well as in allophane, all of which have differing capabilities to retain phosphate. Bulk density is low due to the high porosity resulting from the spherules remaining discrete. Very low bulk densities are found in perhumid climates. Shear strength of allophanic soils is generally less than in non-allophanic soils. This is due to lower cohesion since friction is not altered. Both field moisture and liquid limits tend to be high. Wilting point expressed on a unit-clay basis is also high and like liquid limit it decreases markedly on drying. In very wet climates the wilting point may exceed 100%.     

Effect of some properties on the life of steel discharge blocks in converters

Conclusions Investigations in service and with the regression-correlation analytical method showed that the resistance of experimental blocks, in steel discharge apertures of converters within the limits investigated, is determined mainly by structural characteristics including strength, resistance to abrasion and erosion, pore sizes, and gas permeability.The least wear (0.19 mm per heat) was exhibited by magnesite-chromite refractories made from sinter-active and fine-grained bodies.The wear of the steel discharge blocks is determined mainly by mechanical (abrasion and erosive) action of currents of liquid slag and metal.Translated from Ogneupory, No. 2, pp. 38–44, February, 1973.