The effect of wetting and drying cycles on the swelling-shrinkage behavior of the expansive soils improved by nanosilica and industrial waste

Abstract

The expansive clayey soils show swelling-shrinkage behavior in wetting and drying cycles, respectively. The seasonal water content variations cause large volume changes of expansive clays, and consequently great losses on the infrastructure. In this study, the swelling-shrinkage behavior of a natural severely expansive clay was verified in its natural state and after being improved by nanosilica and industrial waste. Firstly, the swelling potential of the natural soil was determined, and then improvement impacts of different combinations of the stabilizers on the swelling potential were assessed by means of odometer tests. The results indicated that the swelling potential of 1-day-cured samples containing 0.5% of nanosilica decreased from an initial value of 75.26% for the natural expansive clay to 58.1%. The improvement by means of 0.5% of nanosilica and 20% of electric-arc furnace (EAF) slag decreased the swelling potential from an initial value of 75.26% for the natural expansive clay to 17.11%. Afterwards, the wetting and drying cycles’ effects on the swelling and shrinkage of the natural soil and that of the best identified combination of additives were verified by means of a modified odometer. The measurement of the axial deformation of soil, water content, void ratio, and saturation ratio during the swelling-shrinkage cycles indicated that the wetting and drying cycles caused the reduction of swelling potential of both natural and improved expansive soil samples. It was observed that the equilibrium condition occurred in lower number of wetting and drying cycles for the improved sample, compared to that of the natural soil. In addition, for the untreated samples, the highest void ratio and deformation variations occurred at saturation degrees between 50 and 90%. However, for improved soil sample, the highest void ratio and deformation variations were recorded at saturation degrees between 70 and 90%. In comparison with untreated expansive soil, occurring the highest void ratio and deformation variations at the higher saturation ratio reflected the reduction of negative effects of water content variations on volume changes when the expansive soil samples were improved. Based on the experiments performed on both the untreated and treated samples using the scanning electron microscope (SEM) and X-ray diffraction (XRD) tests before and after wetting and drying cycles, it was concluded that the additives used in the study decreased not only the swelling potential of highly expansive soil samples but also the swelling-shrinkage behavior of the soil. Additionally, it increased the durability of the samples during wetting and drying cycles.