Stabilizing collapsible soils using nano calcium carbonate to enhance mechanical properties

Collapsible loess soils exhibit severe volume reduction upon wetting, leading to major geotechnical failures. Conventional stabilizers often fail to provide sufficient improvement in their mechanical behavior, especially under long-term curing conditions. To address these limitations, this study investigates the impact of different contents of nano calcium carbonate (NCC) on improving the mechanical and long-term properties of this soil type. Both destructive tests, including standard compaction, Atterberg limits, the indirect tensile strength (ITS), the unconfined compressive strength (UCS), consolidated-drained direct shear tests and ultrasonic pulse velocity (UPV) test, were conducted. The experimental findings indicated a significant enhancement in strength parameters following the addition of 0.4% NCC, with UCS and ITS increasing by approximately 90% and 155%, respectively. Moreover, as the NCC content increased, reductions of about 8% and 15% were observed in the liquid limit (LL) and plastic limit (PL) of the soil, respectively. This modification also resulted in a 17% increase in the optimum moisture content (OMC), accompanied by a 6% reduction in the maximum dry density (MDD). The long-term soil behavior in the consolidated-drained direct shear test showed that the cohesion and internal friction angle increased by 81% and 7% with increasing curing times of up to 90 days. The mechanical and shear characteristics of soil decreased at NCC content greater than 0.4% due to the agglomeration of nanoparticles and decreased distribution uniformity. Therefore, the optimum content of NCC was determined to be 0.4% to achieve the best mechanical and geotechnical performance. The UPV also demonstrated a direct relationship with the soil's cohesion and internal friction angle, indicating this test's high capability for accurate estimation of soil mechanical characteristics.