Now showing 1 - 10 of 39
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    Understanding the Impact of Lime Stabilization on Expansive Soil for Grounding and Analysis Adopting LIBS
    (01-01-2022)
    Parvathy, G.
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    Babu, Myneni Sukesh
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    Raja, P. Sriram Karthick
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    Harid, Noureddine
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    Griffiths, Huw
    Stabilization of soil for grounding purposes has been performed by adding different wt% of lime. Electrical breakdown measurements under lightning impulse voltage showed a reduction in breakdown voltage and the time to breakdown with increment in the lime content in the soil. These parameters also increased with curing period for all concentrations of lime of stabilized soil samples. The results show that pH and electrical conductivity of the expansive soil increase as the lime content increases, but decrease with increasing the curing period. Mineralogical and micro-structural analysis has been made by means of X-ray diffraction (XRD) studies and by scanning electron microscope (SEM) analysis. The axial strength obtained from unconfined compressive strength (UCS) analysis, the plasma temperature and the electron number density calculated from Laser Induced Breakdown Spectroscopy (LIBS) data tend to increase with increment in lime content as well as the curing period of the lime stabilized soil. Using univariate analysis, the normalized intensity ratio of Ca II peaks from LIBS spectral data are correlated with lime content in the soil samples at various curing periods. The partial least squares regression (PLSR) technique is successful in determining the soil parameters with the help of LIBS spectral data, at different curing periods with an R2 value greater than 0.95 and the percentage RMSE value smaller than 4%.
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    Distress of an industrial building constructed on an expansive soil: A case study from India
    (12-04-2018)
    Ashok Kumar, T.
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    This paper presents a case study of a two-storey building in Oragadam, near Chennai (India), which has undergone distress due to the presence of expansive soil. Undulations in the floors, cracks in partition walls and non-uniform heave in the pavement are some of the failure patterns noticed in and around the structure. Undisturbed soil samples were collected from the site to identify the cause of distress. From the field inspection and laboratory testing it was found that the use of unsuitable fill material (expansive soil) followed by the ingress of excess water from the garden and improper planning of the location of the rainwater-harvesting system were the causes of the initiation of distress in the building.
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    A rapid method of determination of swell potential and swell pressure of expansive soils using constant rate of strain apparatus
    (16-01-2020)
    Ashok Kumar, T.
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    Raheena, M.
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    Swell potential and pressure of expansive soils are conventionally determined using an oedometer apparatus. The specimens are commonly saturated by submerging in water under a seating pressure. Generally, the test takes a long time, as the saturation process is slow. This article presents an improved saturation method by back pressure application in a constant rate of strain (CRS) loading apparatus. Controlled strain loading (CSL) was adopted to bring back the swollen specimens to their initial thickness instead of conventional incremental loading. It is observed that the time taken to complete the test is 7 to 13 times faster compared to the conventional method. When compared to the conventional method, the swell potential and pressure values obtained with the back pressure saturation were found to be higher by about 19 % to 34 % and 6 % to 28 %, respectively. The reason for these higher values is attributed to the attainment of greater saturation using the back pressure saturation technique.
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    Effect of short-term sulphate contamination on lime-stabilized expansive soil
    (01-01-2021)
    Sriram Karthick Raja, P.
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    Lime stabilization is an age-old technique for controlling the swell-shrink characteristics of the expansive soil. However, the presence of sulphate in the expansive soils renders the lime stabilization ineffective due to the formation of detrimental compounds–ettringite and thaumasite. The formation of these detrimental compounds can be counteracted by treatment with low-calcium or non-calcium based stabilizers. However, there is a possibility of sulphate contamination post lime stabilization through external sources. Therefore, the present study brings out the effect of short-term sulphate contamination on lime-stabilized expansive soil using sodium sulphate solution. To achieve this objective, the lime-stabilized expansive soil was cured for 1, 7 and 28 days, and subsequently mixed with sulphate solutions of 5000–20,000 ppm concentration and allowed to equilibrate for 1 day. The experimental results showed that the sulphate contamination had a significant effect on the soil structure, physico-chemical and index properties of lime-stabilized soil. The mechanism governing the deterioration of the stabilized soil depended on the curing period of lime-stabilized soil prior to contamination with sulphate. Short-term sulphate contamination of lime-stabilized soil cured for 1 and 7 days resulted in highly flocculated structure, whereas the lime-stabilized soil cured for 28 days resulted in the formation of ettringite. This is evidenced with the aid of Scanning Electron Microscopy (SEM) images, X-ray diffraction (XRD) and Energy Dispersive X-Ray Analysis (EDAX). It can be concluded from this study that the ettringite formation occurs even after the formation of pozzolanic compounds in lime-stabilized soil.
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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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    Sulfate effects on sulfate-resistant cement–treated expansive soil
    (01-07-2020)
    Raja, P. Sriram Karthick
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    Even though the effectiveness of sulfate-resistant cement (SRC) in stabilizing the high sulfate-bearing expansive soils is proven, its effectiveness in controlling the volume change of expansive soils when exposed to external sulfate contaminants is not known. The physico-chemical and index properties provide basic insight into the volume change behavior of clays. Therefore, this study brings out the effect of external sulfate contamination on the physico-chemical and index properties of SRC-treated expansive soil. Three SRC contents of 5, 10, and 15% were added to the expansive soil separately and reconstituted with distilled water and cured for 1–28 days. After the desired curing period, the SRC-treated expansive soil was reconstituted with sulfate solutions of 5000, 10,000, and 20,000 ppm separately and moisture equilibrated for 1 day for the determination of the properties. The experimental results showed that the SRC treatment increased the pH from 8.75 to 11.95–12.21 and the subsequent sulfate contamination decreased the pH to 9.33–11, where the decalcification of calcium silicate hydrate occurred. Further, the effect of sulfate contamination on liquid limit of SRC-treated soil was negligible, while the plastic and shrinkage limits increased upon sulfate contamination. The increase in the shrinkage limit is attributed to the formation of ettringite/thaumasite in the voids of SRC-treated samples contaminated with 10,000–20,000 ppm sulfate solutions, whereas the monosulfate formation and destruction of cementation gels occurred in samples contaminated with 5000 ppm. These formations are evidenced with the scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction.
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    Influence of osmotic suction on the soil-water characteristic curves of compacted expansive clay
    (01-05-2010) ;
    Rao, Sudhakar M.
    Unsaturated clays are subject to osmotic suction gradients in geoenvironmental engineering applications and it therefore becomes important to understand the effect of these chemical concentration gradients on soil-water characteristic curves (SWCCs). This paper brings out the influence of induced osmotic suction gradient on the wetting SWCCs of compacted clay specimens inundated with sodium chloride solutions/distilled water at vertical stress of 6.25 kPa in oedometer cells. The experimental results illustrate that variations in initial osmotic suction difference induce different magnitudes of osmotic induced consolidation and osmotic consolidation strains thereby impacting the wetting SWCCs and equilibrium water contents of identically compacted clay specimens. Osmotic suction induced by chemical concentration gradients between reservoir salt solution and soil-water can be treated as an equivalent net stress component, (pπ) that decreases the swelling strains of unsaturated specimens from reduction in microstructural and macrostructural swelling components. The direction of osmotic flow affects the matric SWCCs. Unsaturated specimens experiencing osmotic induced consolidation and osmotic consolidation develop lower equilibrium water content than specimens experiencing osmotic swelling during the wetting path. The findings of the study illustrate the need to incorporate the influence of osmotic suction in determination of the matric SWCCs. © 2010 ASCE.
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    Osmotic flow in compacted expansive clay
    (01-04-2015) ;
    Rao, Sudhakar M.
    Depending on the relative chemical concentrations of clay pore water and landfill leachate, three osmotic flow scenarios may be anticipated to dissipate the osmotic suction gradient: outward osmotic flow, inward osmotic flow and no (osmotic) flow. This study examines the volume change behaviour of clay subjected to all osmotic flow conditions. Results show that osmotic suction gradient decreases swelling strains when the osmotic flow is outward, whereas swelling strains increase in case of inward osmotic flow. The increase or decrease in effective stress from osmotic suction gradient is transient and reduces to zero with dissipation of matric suction and osmotic suction gradient. In the no (osmotic) flow condition, the swelling strains are governed by matric suction and pore fluid osmotic suction. The experimental results bring out the dependency of swelling strains on applied stress, stress paths and osmotic suction gradient.