Mitigating Collapse Potential in Gypseous-Sand through Nanoclay Integration: Comparative Oedometer Analysis of Soils

Collapsibility upon wetting is one of the major geotechnical problems associated with gypseous soils, primarily due to gypsum dissolution and the consequent loss of interparticle bonding, which may adversely affect the stability of structures and foundations. This study aims to evaluate the effectiveness of nanoclay in improving the collapse, compressibility, and rebound behavior of two gypseous sandy soils with different gypsum contents: G-29, containing 29% gypsum, and collected from Najaf Governorate, and G-55, containing 55% gypsum and collected from Tikrit Governorate. The behavior of both soils was evaluated using single oedometer tests (SOT), initially in the untreated condition to investigate the effect of gypsum content, and subsequently after treatment with 2%, 5%, and 7% nanoclay by dry weight of soil. The results showed a gradual reduction in collapse potential (CP) with increasing nanoclay content. For G-29, CP decreased from 0.85% to 0.67% at 7% nanoclay, corresponding to an improvement of approximately 21.65% compared with the untreated soil, while for G-55 CP decreased from 2.22% to 1.56%, representing an improvement of approximately 29.55%. Nanoclay treatment also improved rebound behavior during the unloading stage, reducing rebound from 1.8% to 0.8% for G-29 and from 1.2% to 0.6% for G-55 at 7% nanoclay, representing improvements of approximately 55.8% and 52.1%, respectively. Although 7% nanoclay achieved the greatest absolute improvement, the results showed that 5% represented the optimum dosage within the investigated range because increasing the nanoclay content to 7% resulted in only limited additional improvement. The finding highlights that the response of gypseous soil to treatment with nanoclay is influenced by its gypsum content, and demonstrate the potential of nanoclay as an effective stabilization material for reducing collapse and volumetric changes, thereby improving the performance of gypsum soils in geotechnical and foundation applications.