LOAD-SETTLEMENT BEHAVIOUR OF CLAYEY SOIL REINFORCED WITH FLY-ASH + LIME + CLAY COLUMN
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Date
2026
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National Institute of Technology, Silchar
Abstract
Deep-seated medium-soft cohesive soil possess major difficulties in geotechnical engineering because of weak shear-resistance, low-bearing capacity, high compressibility, and tendency to undergo excessive settlement. This study focuses on the utilization of fly-ash which is a waste byproduct in geotechnical application to improve the clayey soil at a reasonable cost and also to provide environmentally sustainable alternative solution. The present study highlights the utilization of fly-ash along with the combination of lime and clay for the construction of Fly-ash+Lime+Clay (FLC) Columns to improve the load carrying capacities of the cohesive soils. The objectives of this study are to firstly determine the optimum percentage of fly-ash, lime and clay to prepare the FLC column. Secondly, to determine the load-settlement behaviour shallow foundation rested on Fly-ash+Lime+Clay column embedded in clayey soil bed by experimental investigation. Another objective is to study the effect of length, spacing, number and confinement of FLC column through numerical analysis using PLAXIS-3D software. To achieve the medium-soft consistency of clayey soil bed UCS sample were prepared at different water content and observed that at 43% water content clay soil attains the UCS value of 29.42 kPa that falls under the medium soft category. To achieve the desired proportion of FLC mix, clayey soil was blended with varying percentages of fly-ash and lime, UCS samples were prepared and tested after curing of 7, 14, and 28 days. The optimum proportion of the FLC mix was found to be 47% Fly-ash, 3% Lime and 50% Clay (F47L3C50). A test-tank of dimension 1m³ was filled with medium-soft cohesive soil up to a depth of 0.9m, and vertical load test was performed on a shallow-foundation of size 0.3m×0.3m×0.05m to determine its capacity. Two FLC column configurations, single and square group with 3D spacing were constructed in clay soil bed, each with a uniform diameter (D) of 50mm and with varying L/D ratios of 6, 8, and 10. Vertical load tests were performed on shallow-foundation of same size rested over FLC column improved clayey soil to determine its capacity. The ultimate load obtained from load settlement graphs demonstrated improvement of capacity as 33.83%, 48.69%, 78.81%, 123.05%, 149.07% and 182.16% respectively for the L/D ratios of 6, 8 and 10, for both single and group column. The load-improvement factor was evaluated for settlements of 5 to 50 mm and the settlement reduction factor was determined for applied loads of 0.2 to 0.8 kN. Load-sharing behaviour between shallow-foundation and FLC column was also evaluated. PLAXIS-3D software was used to perform the parametric study where the effect of length, spacing and pattern of FLC column rested on medium-soft clay bed was studied. The efficiency of FLC column with varying length and spacing was also evaluated. Finally, after summarizing all the results the optimum L/D ratio was fixed as 10, spacing as 2D, and the pattern as square. The findings from both the experimental load tests and the numerical simulations provide practical insights for designing efficient deep stabilization methods for medium-soft clay foundations, ensuring improved strength and load-bearing capacity.