A novel geotechnical approach: non-destructive prediction of strength and swelling behavior of nano-alumina and cement stabilized clays using ultrasonic pulse velocity

In this study, a novel approach was presented for non-destructive prediction of the strength and swelling behavior of expansive clay soils treated with cement and nano aluminum oxide (nano Al₂O₃). Clay soils were stabilized with different cement contents (0%, 3%, and 7% by dry soil weight) and nano-aluminum oxide (0%, 0.3%, 0.6%, 0.9%, 1.2%, and 1.5% by cement weight), and then cured for 7, 28, and 90 days. Destructive tests, including unconfined compressive strength (UCS), indirect tensile strength (ITS), direct shear, unconsolidated-undrained triaxial (UU), swelling tests, and non-destructive ultrasonic pulse velocity (UPV) tests, were performed. Additionally, Microstructural and mineralogical characteristics were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that the addition of cement and nano-aluminum oxide significantly enhanced the strength and reduced the swelling indices. The maximum improvement in UPV and strength was observed at 0.9% nano Al₂O₃. SEM and XRD analyses suggested the development of a denser matrix, with reduced calcium hydroxide content and lower activity of expandable clay minerals. Statistical analysis using response surface methodology (RSM) produced predictive relationships between UPV, maximum dry density, and mechanical, shear, and swelling parameters. The coefficients of determination (R²) reached 0.93 for UCS and 0.96 for cohesion. These findings demonstrate the high potential of the UPV test as an effective non-destructive method for estimating the strength, shear, and swelling behavior of stabilized soils. Moreover, UPV offers a rapid and cost-effective alternative to destructive tests in monitoring and quality control of soil improvement projects.