Synergistic Geotechnical Enhancement of Expansive Regur Soil through Sustainable Composite Stabilization Using Fly Ash, Kota Stone Powder, and Polyolefin Fibre

Abstract

The extensive regur soil is a serious problem for the transportation and foundation infrastructure due to its high swelling potential, low bearing capacity and pronounced shrink-swell behaviour. Industrial waste and synthetic fibres have been extensively studied as individual stabilisers; however, few studies investigated their synergistic performance in composite stabilisation systems. In this work, the effect of ternary stabilisation with Class F fly ash, Kota stone powder and polyolefin fibre on the geotechnical properties of expansive regur soil was studied. Five mixes of 0-25 % fly ash, 0-20 % Kota stone powder and 0-1.0 % polyolefin fibre (by dry weight of soil) were tested for Atterberg limits, Standard Proctor compaction, unconfined compressive strength (UCS), California Bearing Ratio (CBR), free swell index, swelling pressure, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Experimental results were validated using statistical analyses (one-way analysis of variance (ANOVA) and regression modelling). The optimum mixture with 20% fly ash, 15% Kota stone powder and 0.75% polyolefin fibre increased 28-day UCS from 121 to 412 kPa and soaked CBR from 2.8 to 11.9% and decreased plasticity index from 35 to 13%, free swell index from 78 to 22% and swelling pressure from 82 to 23 kPa. SEM showed a denser soil matrix with effective fibre bridging and XRD confirmed the formation of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). The results show that this sustainable composite stabilisation technique is an effective alternative for improving expansive soils used in pavement subgrades, embankments, and shallow foundations.