This research investigated the effect of nano-Al2O3 on the shear and hydraulic properties of collapsible soils. Direct shear, permeability, and consolidation tests were performed on samples stabilized with nano-Al2O3 at different curing times. The results showed that the addition of nano-Al2O3 to collapsible soil led to an increase in shear strength. The cohesion and internal friction angle of stabilized collapsible soil with optimum nano-Al2O3 content (0.6%) increased by 3.25 times and 18%, respectively. Ultrasonic pulse velocity (UPV) measurements demonstrate a significant reduction in void ratio with the addition of nano-Al2O3 and confirm its effectiveness in predicting soil mechanical properties. The R-2 coefficients for estimating cohesion and internal friction angle based on UPV are 0.90 and 0.87, respectively. Moreover, the strong correlation coefficient (0.905) between UPV and the collapse index indicates its significant role in determining soil collapsibility. These results highlight the potential of UPV as a reliable and non-destructive evaluation tool in geotechnical applications. Consolidation test results showed that adding 0.6% nano-Al2O3 to collapsible soil decreased the collapse index by 81%. Nano-Al2O3 with fine-filling properties reduced the permeability coefficient by 87% compared to unstabilized collapsible soil. In general, the results of this research show that using nano-Al2O3 as a stabilizer can significantly improve the characteristics of collapsible soils.

Aeolian and kaolin deposits contribute greatly to infrastructural damage during the rainy seasons because of massive collapse settlements. The prediction of wetting-induced collapse potential and compressibility behavior under partly saturated states is essential for the development of infrastructure on these deposits. In this study, a general constitutive model was developed from the suction-controlled compression and wetting-induced collapse tests. The effect of particle orientation resulting from various initial compaction conditions, drying paths, and wetting paths on the yielding behavior of soil was investigated. A new collapsible soil model (CoSM) was presented by considering the wetting-induced changes to the clay fabric associations in the collapsible soils. The proposed CoSM requires eight parameters for evaluating the mechanical behavior. These model parameters can be readily estimated from simple compression tests, which is the major advantage of the model. The derived equations were capable of predicting three crucial mechanical characteristics, namely, loading-collapse yield, compression, and collapse behavior from the basic compression data. The model shows an excellent agreement with the measured data for two kaolin soils from the present work and several collapsible soils from the literature. The generalized model is capable of predicting mechanical behavior of collapsible soils with various initial compaction states and loading stress histories.