Now showing 1 - 10 of 11
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    Effect of Physico-Chemical Interactions and Cyclic Wet–Dry Process on Behaviour of Compacted Expansive Soils
    (01-02-2021) ;
    Julina, M.
    Physico-chemical interactions and alternate wetting and drying process have marked influence on the swell–shrink and hydraulic behaviour of compacted expansive soils used in various engineering applications. The microstructural, shrinkage cracks pattern and hydraulic behaviour of compacted expansive soils get altered due to the interactions with leachates and cyclic wet–dry process. Therefore, the effect of concentration of leachates and cyclic wetting–drying process on the swell–shrink, shrinkage cracks, microstructural and hydraulic behaviour of compacted expansive soil is studied in this theme lecture paper. The shrinkage cracks developed in clay specimen during a drying cycle were quantified using the X-ray computed tomography images and vernier caliper height measurement. And the same method was used to quantify the cracks in desiccated specimens interacted with different concentrations of interacting fluid. Scanning electron microscope and mercury intrusion porosimeter studies were carried out to understand the microstructure of salt solution-interacted specimens. The influence of physico-chemical interactions and cyclic wet–dry process on the self-healing capacity of compacted expansive soil specimens was brought out by carrying out hydraulic conductivity tests.
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    Effect of hydraulic gradient on swell and hydraulic response of desiccated expansive soil–an experimental study
    (01-01-2022)
    Julina, M.
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    Desiccation cracks in compacted clay liners act as preferential flow paths and affect the hydraulic response during initial stage of wetting. This paper investigates the effect of initial hydraulic gradient on swell, infiltration and hydraulic conductivity during wetting of desiccated expansive soil specimens in oedometric-infiltrometer test set-up. The experimental results on the desiccated specimens demonstrated that the rate of swelling and the infiltration rates in the initial outflow region through the annular gap and permeation outflow region through the swollen soil matrix increased with the increase in hydraulic gradient, whereas the time for reoccurrence of outflow and the establishment of steady state condition decreased. The outflow infiltration rates of the desiccated specimens subjected to initial hydraulic gradients (i) of 2, 5 and 20 reduced from 1.56 × 10−3, 4.83 × 10−3 and 6.57 × 10−2 cm/s, respectively, in the initial outflow region to about 6.65 × 10−6 cm/s (under i= 20) in the permeation outflow region due to the swelling of the desiccated expansive soil. The minimum possible initial hydraulic gradient that can be adopted on desiccated expansive soil specimens during infiltration testing was found to be 2 without considering the infiltration driven by soil suction.
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    Combined effects of wet-dry cycles and interacting fluid on desiccation cracks and hydraulic conductivity of compacted clay
    (20-03-2020)
    Julina, M.
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    Compacted clays are used as barriers in landfills mainly due to their low hydraulic conductivity and self healing properties. These clays are subjected to moisture fluctuations and simultaneously exposed to leachates. Besides swelling, the shrinkage and cracks developed during drying get altered due to their exposure to contaminants and control their hydraulic behaviour. Therefore, this paper quantifies the volumetric behaviour and cracks pattern of compacted clay exposed to salt solutions during wet-dry cycles using X-ray computed tomography (XCT) imaging experiments. The results showed that the cracks volume of clay specimen interacted with 4 M NaCl solution is significantly greater than the specimens interacted with distilled water (DW) and 0.4 M NaCl solution at the end of drying cycles. XCT and digital camera imaging experiments showed that the cracks did not develop at same locations in specimen interacted with DW, indicating the self healing property of clay. However, the development of cracks at same locations in specimen interacted with 4 M NaCl solution indicates the complete deterioration of self healing property of clay. This resulted in significantly higher hydraulic conductivity of compacted specimen interacted with 4 M NaCl solution than the specimens interacted with DW and 0.4 M NaCl solution at the end of different wetting cycles.
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    Determination of volumetric shrinkage of an expansive soil using digital camera images
    (01-01-2021)
    Julina, M.
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    The volume change during drying of compacted expansive soils occurs in the form of reduction in overall volume and development of cracks. Accurate determination of volume of shrunken soil specimens becomes essential to understand the shrinkage behaviour of compacted expansive soils. Mercury displacement method available for the bulk volume measurement of cylindrical small samples suffers from the serious limitations such as the restrictions of using the mercury as it is a hazardous material and the size of specimens is limited to small samples/portions. In the past few years, the digital camera images have been successfully utilised in studying the crack pattern and various parameters associated with reconstituted soils dried from slurry state. Fewer works have been carried out to quantify the cracks in the compacted soils, especially in compacted expansive soils. In this paper, simple methods for the determination of the volume of shrunken soil specimens excluding the volume of cracks are proposed based on the digital camera images captured on thin oedometer shrunken soil specimen along with the vernier calliper method. The results were compared with the mercury displacement method. Cracks which extended from top to bottom of the shrunken specimen during drying assisted in employing these methods. The effect of cracks on shrinkage deformations during second drying cycle and at the end of five drying cycles under a vertical stress of 12.5 kPa was studied.
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    Effect of induced osmotic suction on swell and hydraulic conductivity of an expansive soil
    (01-01-2019)
    Julina, M.
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    Compacted expansive soils are widely used as engineered barriers in waste contaminant applications like landfills, brine ponds, and nuclear waste disposal sites. These liners are designed for very low hydraulic conductivity (<1 × 10−7 cm/s). Percolation of chemical waste or leachate results in physicochemical changes in compacted expansive soils which increases the hydraulic conductivity. This paper brings out the changes in swelling behavior and hydraulic conductivity of compacted expansive soil induced with osmotic gradients using NaCl and CaCl2 solutions. Multiple identical soil specimens placed in oedometer assemblies were inundated with distilled water, 0.4 and 4 M NaCl (monovalent cations), and 0.4 and 4 M CaCl2 (divalent cations) salt solutions and allowed to swell under a surcharge pressure of 12.5 kPa. Void ratio–water content plots were also traced during swelling process. Falling head permeability tests were conducted on swollen soil specimens in rigid wall oedometer permeameters under a hydraulic gradient (i) of 20. The experimental results showed that the swell potentials reduced and hydraulic conductivity increased with the increase in induced osmotic suction.
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    Effect of Remoulding Water Content on Hydraulic Response of a Compacted Expansive Soil
    (01-01-2023)
    Julina, M.
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    The microstructure of compacted expansive soils differs depending on the remoulding water content and compaction dry density. In particular, along the standard Proctor compaction curve, the expansive soil compacted at water content less than the optimum water content has relatively larger macropores in comparison to the expansive soil compacted at water contents greater than the optimum water content. These changes in microstructure not only influence the hydraulic conductivity but also the infiltration rates during the swelling process of compacted expansive soils. Therefore, this paper brings out the effect of remoulding water content on the infiltration rates during swelling process and hydraulic conductivity at the end of swelling process of a compacted expansive soil. The oedometric-infiltrometer test arrangement was used to determine the hydraulic response, in terms of infiltration rates and hydraulic conductivity, upon inundation of the compacted expansive soil specimens remoulded with water contents corresponding to dry and wet side of optimum water contents at the same standard Proctor compaction dry density. As expected at the end of swelling process, the swell magnitude and hydraulic conductivity were relatively higher for the clay specimen compacted at dry of optimum water content. In addition, the infiltration test results showed that the time needed for the outflow (i.e. permeation flow) to occur and attain a steady state condition was comparatively less for the compacted clay specimen compacted at dry of optimum water content than at wet side of optimum water content. The changes in dry density and water content during the swelling process of compacted clay specimens were also traced.
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    Effect of pore fluid and wet-dry cycles on structure and hydraulic conductivity of clay
    (01-01-2019) ;
    Julina, M.
    Compacted clays in landfill applications are subjected to both physico-chemical changes and wet–dry cycles. Physico-chemical interactions occur at the microstructural level between the clay particles and chemical constituents such as brine solutions or leachates generated from landfill waste. Furthermore, the volumetric changes during wetting and drying also cause microstructural changes to compacted clays. The microstructural changes due to the physico-chemical interactions and wet–dry cycles are reflected at the macrostructural level and govern the macro-behaviour of compacted clays. Therefore, this paper brings out the combined effect of the interacting fluid and wet–dry cycles on volume change, microstructure and hydraulic conductivity of compacted clay soil. To achieve this, the compacted clay specimens were inundated with distilled water and sodium chloride (NaCl) solutions during wetting cycles. The experimental results showed that the ability of clay particles to swell at microstructural level and decrease the size of macropores in compacted clay was completely lost with 4 M sodium chloride solution and with increase in wet–dry cycles. Thus, the hydraulic conductivity of compacted clay specimen inundated with 4 M sodium chloride solution was unusually high at the end of the second and further wetting cycles even when subjected to higher effective confining pressures.
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    Collapse Behaviour of Compacted Coal Ashes
    (01-03-2016) ;
    Bhavani, P.
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    Das, Amiya Prakash
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    Julina, M.
    Coal ash is a by-product produced from the thermal power plants. It is characterized with low unit weight, high shear strength and low compressibility and finds a major application as an alternate material in the geotechnical engineering applications. However, some coal ash fills are susceptible to wetting-induced collapse due to the loss of capillary suction which stabilizes the inter-granular bonds. The present study examines the influence of placement conditions, vertical stress and pore fluid concentration on the collapse behaviour of compacted fly ash specimens. The experimental results showed that the maximum collapse potential for the coal ash specimens compacted to relative compaction of 80 % and water content of 15 % was in the range of 8.6–13 % at vertical stress of 100 kPa, which indicates that the apparent preconsolidation stress for the coal ash specimens is equal to 100 kPa. Among the coal ashes, the compacted fly ash specimens are more susceptible to wetting-induced collapse in comparison to bottom ash and pond ash specimens which is attributed to the higher silt size fraction in the fly ash. This study also presents the collapse behaviour of lime stabilized compacted coal ash.
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    Quantification of desiccation cracks using X-ray tomography for tracing shrinkage path of compacted expansive soil
    (12-02-2019)
    Julina, M.
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    Compacted expansive soils undergo large volumetric changes during wet–dry cycles owing to the seasonal moisture fluctuations, and during drying the shrinkage is accompanied with the desiccation cracks. This paper presents the shrinkage behaviour of compacted expansive soil specimen, under a vertical stress of 12.5 kPa, in terms of void ratio–water content plot during second drying cycle. Accurate characterization of shrinkage behaviour along with the soil–water characteristic curve in terms of degree of saturation versus water content helps in the development of constitutive relation such as void ratio–suction relationship, which is vital for the prediction of unsaturated soil properties. However, the expansive soils develop large desiccation cracks during drying, which hinder the accurate volume measurement of desiccated soil specimen using vernier caliper as the vernier caliper measurements do not capture the volume of cracks developed within the soil specimen. The mercury displacement method and fluid displacement methods measure the volume of the soil specimens accurately, but the methods are either destructive or hazardous, and consequently, the continuous measurements are not possible. In order to overcome these limitations, the XCT imaging experiments were carried out along with the image analysis technique using ImageJ software and vernier caliper height measurements for tracing the volume change during the second drying path. The exact volume change during and at the end of drying process was estimated by deducting the cracks volume from the volume of specimen arrived from the vernier caliper measurements. Also the volume change at the end of drying process was measured using both XCT imaging experiments and mercury displacement method, and the results were compared. The cracks volume was used for defining the void ratios pertaining to specific components like cracks void ratio, annular gap void ratio, discontinuities void ratio (annular gap + cracks), soil pores void ratio and total void ratio (including and excluding the annular gap). The experimental results in terms of void ratio pertaining to various components, during drying process, were presented in terms of void ratio–water content plots and compared with the void ratio–water content plot of specimen reconstituted from slurry. The void ratio–matric suction constitutive relationship was developed from the void ratio–water content plot and soil–water characteristic curve.
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    Shrinkage behaviour of slurry-consolidated and compacted clay soil
    (01-01-2022)
    Julina, M.
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    This research investigates the shrinkage behaviour of clay specimens subjected to different hydraulic paths. The volume change and microstructure of desiccated clay specimen directly dried from reconstituted slurry and compacted states, and the desiccated clay specimens obtained by subjecting the as-compacted clay specimen to cyclic wetting and drying process were compared. The experimental results showed that the initial microstructural difference between reconstituted slurries and compacted specimens influences their shrinkage behaviour. The compacted clay specimens retained the bimodal structure even after subjecting to cyclic wetting and drying, unlike the reconstituted slurry, which showed a predominant unimodal structure at the end of drying process. This is due to the absence of large macropores in the desiccated clay specimen dried from reconstituted slurry state, which is evidenced from the mercury intrusion porosimetry studies, scanning electron microscopy and nano-focus X-ray-computed tomography imaging experiments.