Experimental investigation of thixotropic hardening of selected clays

Abstract

This study investigates the thixotropic hardening behavior of reconstituted clay soils from Gazipur, Savar, and Mohakhali in Bangladesh, examining the impact of thixotropic aging on their strength recovery, deformation characteristics, and microstructural changes over 48 days. Utilizing advanced analytical techniques, including X-ray Diffraction (XRD), X-ray Fluorescence (XRF), and Scanning Electron Microscopy (SEM), this research comprehensively assesses the role of clay mineralogy, particle arrangement, and water content in enhancing the engineering properties of these soils, with significant implications for geotechnical design and construction. The methodology involved collecting both disturbed and undisturbed soil samples using wash boring and Shelby tube sampling techniques. These samples were then naturally dried, ground, and sieved to prepare reconstituted specimens at their respective liquid limits. A series of laboratory tests, including unconfined compressive strength (UCS), triaxial compression, and one-dimensional consolidation, were conducted at various aging intervals up to 42 days. These tests were complemented by detailed mineralogical and microstructural analyses to determine specific gravity, Atterberg limits, and particle size distribution, revealing variations in fines content ranging from 89.6% to 98.63% and specific gravity values between 2.63 and 2.7. Significant findings from the study highlight a pronounced time-dependent strength recovery, especially notable in Mohakhali soil, which demonstrated the highest increase in unconfined compressive strength, escalating from 60.8 kPa to 87.5 kPa. The research introduced and utilized the Thixotropic Strength Ratio (TSR) and Thixotropic Regain Strength Ratio (Bt) to effectively quantify the recovery, capturing the reformation of particle structures and bond enhancement post-disturbance. Triaxial test results showed a remarkable 144% increase in deviator stress under a consolidation pressure of 120 kPa over 28 days. Microstructural analyses via SEM revealed densification and improved particle alignment, enhancing soil mechanical properties. XRD and XRF identified mineral variations influencing strength recovery, with higher illite in Mohakhali soil enhancing cohesion and thixotropy. Elevated alumina and iron oxide further improved particle bonding and strength regain. These findings highlight the critical role of mineralogy and microstructure in thixotropic behavior, providing valuable insights for geotechnical applications in clay-rich environments.