Strength improvement of coastal silty deposits using cement and nano-Al 2 O 3 : A geotechnical and microstructural study

Silty soils are widely encountered in coastal zones, especially in estuarine and nearshore areas. However, their stabilization using nano-materials has received limited attention. This study explores the geomechanical and microstructural improvement of a coastal low-plasticity silt treated with various dosages (0%–4%) of cement and nano-aluminum oxide (nano-Al2O3). A series of unconfined compressive strength (UCS), direct shear, and scanning electron microscopy (SEM) tests were conducted. Results showed that at 4% cement, increasing nano-Al2O3 from 0% to 1% enhanced UCS by 81% (7 days) and 38.6% (28 days), while stiffness (E50) rose by 177% and 136%, respectively. Similarly, cohesion increased by 110% and 101% at 8% cement for the same curing periods, followed by only modest gains at higher nano contents. The internal friction angle followed a similar trend. SEM analysis, supported by quantitative pore assessment using ImageJ, revealed a denser and more cohesive matrix at 1% nano-Al2O3, while higher contents disrupted the structure due to agglomeration. This study also performed a comparative sensitivity analysis using multiple linear regression and cosine amplitude method to identify and contrast the most influential parameters affecting strength development. The findings support the combined use of cement and nano-Al2O3 for coastal silty soil stabilization.