Reduction of Expansive Index,Swelling and Compression Behavior of Kaolinite and Bentonite Clay with Sand and Class C Fly Ash

Swelling behavior of expansive soil has always created problems in the field of geotechnical engineering. Generally, the method used to assess the swelling potential of expansive soil from its plasticity index, shrinkage limit and colloidal content. Alternative way to evaluate swelling behavior is from its expansive index (EI) and swelling pressure value. The present study investigates the reduction of EI and swelling pressure for kaolinite and bentonite clay when mixed with various percentages of Ottawa sand and Class C fly ash. The percentages of Ottawa sand and Class C fly ash used were 0–50 % by weight. The results show that there is a significant reduction in the swelling properties of expansive soil with the addition of Ottawa sand and Class C fly ash. The reduction in EI ranged approximately from 10 to 50 and 4 to 49 % for kaolinite and bentonite clay, respectively. Also the maximum swelling pressure of kaolinite and bentonite clay decreased approximately 93 and 64 %, respectively with the addition of various percentages of Ottawa sand and Class C fly ash. Standard index properties test viz., liquid limit, plastic limit and linear shrinkage test were conducted to see the characteristics of expansive soil when mixed with less expansive sand and fly ash. Also, for these expansive soils one dimensional consolidation test have been conducted with sand and fly ash mixtures and the results were compared with pure kaolinite and bentonite clay.     

Silica fume stabilization of an expansive clay subgrade and the effect of silica fume-stabilised soil cushion on its CBR

ABSTRACT

Expansive soil subgrades, which are subjected to dual swell-shrink problem consequent upon absorption and evaporation of water, need to be improved by chemical stabilization or compacted cushion or geosynthetic reinforcement in order that pavements constructed over them are even, stable and safe. This paper presents extensive experimental data on plasticity, free swell index (FSI) and compaction characteristics of a highly swelling expansive clay stabilized with varying silica fume contents. In another series of tests on a laterite soil to be used as a cushion over the expansive clay subgrade, plasticity properties, compaction characteristics and strength characteristics were determined at varied silica fume contents. Further, CBR of the expansive clay subgrade was determined in the laboratory stabilizing it with varied silica fume contents and providing a cushion of 50 mm thickness of silica fume-stabilized lateritic soil. Liquid limit (LL), plasticity index (PI) and free swell index (FSI) of the expansive clay decreased with increasing silica fume contents. The compaction and strength characteristics of both the soils improved with silica fume stabilization. The CBR of the expansive clay provided with silica fume-stabilized cushion improved significantly.     

Effect of lime and fly ash on swell,consolidation and shear strength characteristics of expansive clays: a comparative study

Expansive soils swell on absorbing water and shrink on evaporation thereof. Because of this alternate swelling and shrinkage, civil engineering structures founded in them are severely damaged. For counteracting the problems of expansive soils, different innovative techniques were suggested. Stabilization of expansive clays with various additives has also met with considerable success. This paper presents, by comparison, the effect of lime and fly ash on free swell index (FSI), swell potential, swelling pressure, coefficient of consolidation, compression index, secondary consolidation characteristics and shear strength. Lime content (weight of lime/weight of dry soil) was varied as 0%, 2%, 4%?and 6%?and fly ash content (weight of fly ash/weight of dry soil) as 0%, 10%?and 20%. A fly ash content of 20%?showed significant reduction in swell potential, swelling pressure, compression index and secondary consolidation characteristics and resulted in increase in maximum dry density and shear strength. Swell potential and swelling pressure decreased with increase in lime content also. Further, consolidation characteristics improved. Compaction characteristics and unconfined compression strength improved at 4%?lime and reduced at 6%?lime.     

Behavior of expansive soils stabilized with fly ash

Expansive soils cause serious problem in the civil engineering practice due to swell and shrinkage upon wetting and drying. Disposal of fly ash, which is an industrial waste in both cost-effective and environment-friendly way receives high attention in China. In this study, the potential use and the effectiveness of expansive soils stabilization using fly ash and fly ash-lime as admixtures are evaluated. The test results show that the plasticity index, activity, free swell, swell potential, swelling pressure, and axial shrinkage percent decreased with an increase in fly ash or fly ash-lime content. With the increase of the curing time for the treated soil, the swell potential and swelling pressure decreased. Soils immediately treated with fly ash show no significant change in the unconfined compressive strength. However, after 7 days curing of the fly ash treated soils, the unconfined compressive strength increased significantly. The relationship between the plasticity index and swell-shrinkage properties for pre-treated and post-treated soils is discussed.     

Global representation of the drying–wetting curves of four engineering soils: experiments and correlations

The main objective of this paper is to examine how different engineering soils react to environmental variations and to provide correlations to characterize their behaviour under null external mechanical stress. Two French and two Algerian soils with liquid limits ranging from 36 to 112 were prepared under both slurry and Proctor compaction conditions, and then subjected to drying–wetting paths with suction controlled from several kPa to several hundreds of MPa. Experimental results are presented in five diagrams to show globally and simultaneously the shrinkage–swelling, saturation–desaturation and water retention characteristics. A reasonable consistency was observed between the oedometric and drying curves of slurry, confirming the equivalence between hydraulic loading (suction) and mechanical loading (consolidation stress) on the volume change behaviour of different soils. As an intrinsic parameter of soil nature, liquid limit was found to have a significant influence on the shrinkage limit, air-entry suction and compressibility of both slurry and compacted samples. For that reason, correlations between these characteristics and liquid limit were set up, providing a good basis for a first estimation of the drying–wetting curves. At the micro-scale, new experimental results were obtained: either on drying or wetting path, the micro-pores were almost unaffected, whereas, when matrix suction increased from 0.1 to 8 MPa, the volume of macro-pores decreased to quasi-closure. At last, the analogy between the compaction and drying–wetting curves, and the comparison of different methods to determine the water retention curve were addressed. Such analogies and comparisons contribute to a better understanding of the mechanisms of mechanical stress and suction.     

Coupled consolidation model for negative skin friction on piles in clay layers

Expansive soils swell on absorbing water and shrink on evaporation thereof. Because of this alternate swelling and shrinkage, civil engineering structures founded in them are severely damaged. For counteracting the problems of expansive soils, different innovative techniques were suggested. Stabilization of expansive clays with various additives has also met with considerable success. This paper presents, by comparison, the effect of lime and fly ash on free swell index (FSI), swell potential, swelling pressure, coefficient of consolidation, compression index, secondary consolidation characteristics and shear strength. Lime content was varied as 0%, 2%, 4%?and 6%?and fly ash content as 0%, 10%?and 20%. A fly ash content of 20%?showed significant reduction in swell potential, swelling pressure, compression index and secondary consolidation characteristics and resulted in increase in maximum dry density and shear strength. Swell potential and swelling pressure decreased with increase in lime content also. Further, consolidation characteristics improved. Compaction characteristics and unconfined compression strength improved at 4%?lime and reduced at 6%?lime.     

粉煤灰改良膨胀土试验研究

研究掺粉煤灰对合肥膨胀土的物理性质指标以及胀缩性指标等的影响,探讨利用粉煤灰改良膨胀土的措施与效果。试验研究结果表明,在膨胀土中掺入适量的粉煤灰可有效降低膨胀土的塑性指数、降低膨胀势、减小线缩率与降低活性。在膨胀土中掺入粉煤灰还可改变膨胀土的击实特性,一定击实功作用下,随着掺灰率的增加,土体的最优含水率与最大干密度均减小,膨胀土中掺入粉煤灰后,膨胀土可在较小的含水率下通过击实或压实达到稳定。掺灰膨胀土的膨胀量与膨胀力随养护龄期的增长而减小;没有经过养护的掺灰土,其无侧限抗压强度随掺灰率的变化几乎没有变化,经过7 d养护后,土的无侧限抗压强度有所增长,并且存在一个峰值点,合肥膨胀土的无侧限抗压强度所对应的最佳掺粉煤灰率约为15 %～20 %。     

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.     

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.     

膨胀土胀缩性评价中有关问题的研究

膨胀土吸水膨胀、失水收缩,产生地表变形,进而导致建筑物破坏。本文就现行膨胀土胀缩性指标试验及地基变形量评价计算中有关问题进行了研究,认为以天然含水量为起始含水量测定土样胀缩率是不合适的,建议以缩限为起点进行膨胀试验,以胀限为起点进行收缩试验,采用加荷膨胀量（而非卸荷膨胀量）参加有荷载下的膨胀率计算。膨胀土地基勘察必须结合场地条件分析可能影响土体含水量变化的因素,对同一工程采用几种方法评价,互相对比、参照。     

Physical and Compaction Behaviour of Clay Soil–Fly Ash Mixtures

At present, nearly 100 million tonnes of fly ash is being generated annually in India posing serious health and environmental problems. To control these problems, the most commonly used method is addition of fly ash as a stabilizing agent usually used in combination with soils. In the present study, high-calcium (ASTM Class C—Neyveli fly) and low-calcium (ASTM Class F—Badarpur fly ash) fly ashes in different proportions by weight (10, 20, 40, 60 and 80 %) were added to a highly expansive soil [known as black cotton (BC) soil] from India. Laboratory tests involved determination of physical properties, compaction characteristics and swell potential. The test results show that the consistency limits, compaction characteristics and swelling potential of expansive soil–fly ash mixtures are significantly modified and improved. It is seen that 40 % fly ash content is the optimum quantity to improve the plasticity characteristics of BC soil. The fly ashes exhibit low dry unit weight compared to BC soil. With the addition of fly ash to BC soil the maximum dry unit weight (γ_dmax) of the soil–fly ash mixtures decreases with increase in optimum moisture content (OMC), which can be mainly attributed to the improvement in gradation of the fly ash. It is also observed that 10 % of Neyveli fly ash is the optimum amount required to minimize the swell potential compared to 40 % of Badarpur fly ash. Therefore, the main objective of the study was to study the effect of fly ashes on the physical, compaction, and swelling potential of BC soils, and bulk utilization of industrial waste by-product without adversely affecting the environment.     

石灰改良膨胀土力学性质的研究

膨胀(?)主要是由强亲水性粘土矿物蒙脱石和伊利石组成的,是具有膨胀性、多裂隙性和超固结性的高塑性粘性土。在铁路施工中,膨胀土不能直接作为路基填土,必需进行改良。通过室内试验的方法来讨论石灰改良膨胀土的力学性质在各种影响因素下的变化规律。     

Desiccation-induced Shrinkage in Compacted Lateritic Soils

Specimens prepared from three lateritic soil samples were subjected to drying under laboratory conditions. Volumetric shrinkage strains were measured at the end of the drying period. Results of this study indicate that, for the lateritic soils tested, volumetric shrinkage strains are influenced by soil composition and compaction conditions. Volumetric shrinkage strain increased with higher compaction water content. The influence of compaction water content on measured volumetric shrinkage strain was more pronounced in specimens with higher fines content. A regression equation was developed from the data to estimate volumetric shrinkage strain given the compaction water content relative to optimum, plasticity index, fines content and compactive effort.     

Property Correlations and Statistical Variations in the Geotechnical Properties of (CH) Clay Soils

This study was focused on the correlations between the physical and mechanical properties and geostatistical analysis of the clay of high plasticity (CH) soil based on the experimental data and the data collected from various research studies. Four types of CH soil with liquid limit (LL) of 50, 62, 76 and 88% were collected from the field, tested, compared with the data from literature and qualified using hyperbolic model. X-ray diffraction analyses showed the major constituents of the CH soil with LL of 50% were calcium silicate (Ca₂SiO₄), aluminum silicate (Al₂SiO₅) and quartz (SiO₂) and the major constituents of the CH soil with LL of 88% were montmorillonite (Na, Ca) _0.33(Al, Mg) ₂(Si₄O₁₀) (OH)₂·nH₂O, kaolinite (Al₂Si₂O₅(OH)₄) and quartz (SiO₂). The index properties, compacted properties, free swelling and compressive strength of the CH soils were investigated and quantified with over 1000 data collected from the literature. Using the mean (μ), standard deviation (σ), variation (σ²) and coefficient of variation parameters of CH soils properties such as density (γ), index properties (LL and PL), compaction properties (OMC and γ_dmax), swelling index (FS), initial void ratio (e_o), compression index (Cc) and undrained shear strength (S_u) properties were also studied. Liquid limit of CH soils varied between 50 and 110% and plasticity index varied between 26 and 72%. The wet unit weight (γ_wet) for the CH soils varied from 1.30 to 2.19 g/cm³. Undrained shear strength (S_u) of CH soils were varied from 10 to 184 kPa and quantified very well as a function of liquid limit, plasticity index, moisture content and dry density using the experimental data and data collected from the literature.     

Analysis of Swelling and Shrinkage Behavior of Compacted Clays

The impact of the variation in compaction condition on the swelling and shrinkage behavior of three soils has been examined. Two natural soils, namely red soil and black cotton soil, and one artificially mixed soil sample of commercial bentonite with well-graded sand, were studied. Compaction curve for Standard Proctor conditions were plotted and four compaction conditions were selected. Experimental results showed that clay mineralogy dominates over compaction conditions in influencing the swelling and shrinkage behavior of the tested soils. Monitoring of void ratio (e)−water content (w) relations during shrinkage showed that soil specimens generally shrunk in three distinct linear stages. A small reduction in void ratio occurred on reduction in water content during the first shrinkage stage and was termed as initial shrinkage. In second stage, void ratio decreased rapidly with reduction in water content and was termed as primary shrinkage. In third and final stage, reduction in water content is accompanied by a marginal change in void ratio and it’s called residual shrinkage. Irrespective of initial compaction conditions studied, the transition from primary to residual shrinkage for all the specimens occurred within a narrow range of water content (10–15%).     

Compaction characteristics of granular soils in United Arab Emirates

Most of the topsoils encountered in United Arab Emirates and in the Arabian Peninsula are granular soils with small percentages of silt and clay. Determination of the compaction characteristics of such soils is an essential task in preparing for construction work. The accumulating experience over many years of soil testing in our laboratories suggested that there exists an underlying trend that governs the compaction characteristics of such soils. As such, a study was undertaken to assess the compaction characteristics of such soils and to develop the governing predictive equations. For the purposes of this study, 311 soil samples were collected from various locations in the United Arab Emirates, and tested for various including grain-size distribution, liquid limit, plasticity index, specific gravity of soil solids, maximum dry density of compaction, and optimum moisture content following ASTM D 1557-91 standard procedure C. Following the development of the predictive equations, a new set of 43 soil samples were collected and their compaction results were used to test the validity of predictive model. The range of variables for these soils were as follows: percent retained on US sieve #4 (R#4): 0–68; Percent passing US sieve #200 (P#200): 1–26; Liquid limit: 0–56; Plasticity index: 0–28; Specific gravity of soil solids: 2.55–2.8. Based on the compaction tests results, multiple regression analyses were conducted to develop mathematical models and nomographic solutions to predict the compaction properties of soils. The results indicated that the nomographs could predict well the maximum dry density within ±5% confidence interval and the optimum moisture content within ±3%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of Swelling and Shrinkage Properties of Undisturbed Expansive Soils

Expansive soils exhibit large volume changes when their water content changes. Alternate heave and settlement due to seasonal climatic variations result in distress and damage in civil infrastructure systems. This research focuses on the understanding of swelling and shrinkage phenomenon in the surface layer of expansive soils. Undisturbed field samples were used to capture the effect of in situ conditions (geologically induced fissuring and environmentally caused saturation) on volume change properties of Regina clay. Based on laboratory investigations, the swelling potential and swelling pressure of the native clay at S = 82% were found to be 1.5% and 3.5 kPa, respectively. The swell-shrink path during progressive soil drying followed an S-shaped curve comprising of an initial low structural shrinkage followed by a sharp decline during normal shrinkage and then by a low decrease during residual shrinkage. The soil microstructure correlated well with the observed volume change behaviour as well as with the consistency limits. The presence of fissures in field samples at various degrees of saturation confirmed that the investigated deposit is at an equilibrium condition with respect to the swell-shrink phenomenon. The swelling properties at any initial saturation state were estimated using the free swelling test and the swell-shrink test data in conjunction. The swelling potential increased 12 times (from 2 to 24%) and the swelling pressure increased by two orders of magnitude (from 27 to 2500 kPa) with a change in the degree of saturation from 80% (at the plastic limit) to 60% (at the shrinkage limit).     

Effects of surfactants and electrolyte solutions on the properties of soil

Biosurfactants are frequently used in petroleum hydrocarbon and dense non-aqueous phase liquids (DNAPLs) remediation. The applicability of biosurfactant use in clayey soils requires an understanding and characterization of their interaction. Comprehensive effects of surfactants and electrolyte solutions on kaolinite clay soil were investigated for index properties, compaction, strength characteristics, hydraulic conductivities, and adsorption characteristics. Sodium dodecyl sulfate (SDS) and NaPO₃ decreased the liquid limit and plasticity index of the test soil. Maximum dry unit weights were increased and optimum moisture contents were decreased as SDS and biosurfactant were added for the compaction tests for mixtures of 30% kaolinite and 70% sand. The addition of non-ionic surfactant, biosurfactant, and CaCl₂ increased the initial elastic modulus and undrained shear strength of the kaolinite–sand mixture soils. Hydraulic conductivities were measured by fixed-wall double-ring permeameters. Results showed that the hydraulic conductivity was not significantly affected, but slightly decreased from 1×10⁻⁷ cm/s (water) to 0.3×10⁻⁷ cm/s for Triton X-100 and SDS. The adsorption characteristics of the chemicals onto kaolinite were also investigated by developing isotherm curves. SDS adsorbed onto soil particles with the strongest bonding strength of the fluids tested. Correlations among parameters were developed for surfactants, electrolyte solutions, and clayey soils.     

黄河冲积平原低液限土的工程特性研究

依托济南—乐陵高速公路路基勘察项目,依据试样的室内土工试验成果,应用回归分析方法,建立了黄河冲积平原低液限土的含水率与土的密度、孔隙比和压缩系数及土的塑性指标等相关经验公式;对区内赋存的低液限粉质黏土,通过与其他相近密实度的土,在抗剪强度及单向固结条件下固结特性的比较分析,指出该区域此类土质具有所谓的"高密度、低强度、中(偏高)压缩性"的工程特性。     

Evaluation of the compression index of soils using an artificial neural network

The compression index is a one of the important soil parameters that is essential to geotechnical designs. As the determination of the compression index from consolidation tests is relatively time-consuming, empirical formulas based on soil parameters can be useful. Over the decades, a number of empirical formulas have been proposed to relate the compressibility to other soil parameters, such as the natural water content, liquid limit, plasticity index, specific gravity, and others. Each of the existing empirical formulas yields good results for a particular test set, but cannot accurately or reliably predict the compression index from various test sets. In this study, an alternative approach, an artificial neural network (ANN) model, is proposed to estimate the compression index with numerous consolidation test sets. The compression index was modeled as a function of seven variables including the natural water content, liquid limit, plastic index, specific gravity, and soil types. Nine hundred and forty-seven consolidation tests for soils sampled at 67 construction sites in the Republic of Korea were used for the training and testing of the ANN model. The predicted results showed that the neural network could provide a better performance than the empirical formulas.