Effect of Colloidal Nanosilica Grouting on Collapse Potential and Unconfined Compression Strength of Collapsible Soils

In geotechnical engineering, nanosilica is recognized as an environmentally friendly additive for soil improvement. The low viscosity and controllable solidification rate of colloidal nanosilica grout (CNS) make it an excellent solution for improving soil quality through injection under low pressure. In this study, the effects of injecting different concentrations of CNS grout (5%, 10%, 15%, 20%, and 25% by weight (wt%)) on reconstituted specimens of collapsible soil were investigated using scanning electron microscope (SEM) images and unconfined compression and collapse potential tests. According to the SEM images, as the concentration of colloidal nanosilica grout increased, the coverage of nanosilica on the surface of the soil grains and the number of bonds among the soil particles increased. The cementation level was determined by measuring the dry weight of the cemented samples. The results of collapse potential tests indicated a significant decrease in the collapse index of non-cemented soil from severe to moderate–severe or moderate degrees for cemented specimens. Furthermore, as the concentration of CNS grout increased, the uniaxial compressive strength of the specimens increased. After evaluating factors such as injectability, improvement in collapse index and uniaxial strength, and the associated improvement costs, a concentration of 20 wt% was determined to be the optimal concentration for CNS grout.