The effect of wetting and drying cycles on the swelling-shrinkage behavior of the expansive soils improved by nanosilica, polypropylene fibres and EAF slag

The problematic expansive soils are spread in all parts of the world. The water content variations cause large soil volume changes and consequently, great losses on the infrastructure. The expansive clayey soils show swelling - shrinkage behaviour respectively in wetting and drying cycles. In this study, the swelling-shrinkage behaviour of a natural severely expansive bentonite was verified in its natural state and after being improved by nanosilica, polypropylene fibres, and the EAF slag. Firstly, the swelling potential of the natural soil was determined and then, different combinations of the stabilizerschr('39') effects on the swelling potential were assessed by means of oedometer tests under 1 kPa loading. The swelling potential of the untreated expansive clay sample was measured as 75.26%, thus the soil sample provided for the study was considered in the very high expansion category. The results indicated that the swelling potential of one-day cured samples by the addition of 0.5% of nanosilica decreased by 22.8%. The improvement by means of 0.5% of nanosilica and 0.6% of polypropylene fiber, and the optimum composition of 0.5% of nanosilica, 0.6% of polypropylene fibers, and 10% of EAF slag decreased the swelling potential by 70 and 85%, respectively. Afterwards, the wetting and drying cycleschr('39') effects on the swelling and shrinkage of the natural soil and that of the best identified combination of additives were verified by means of modified oedometer. The measurement of the axial deformation of soil, void ratio, and the saturation ratio during the swelling-shrinkage cycles indicated that the wetting and drying cycles caused the reduction of swelling potential of both untreated/natural and improved expansive soil samples. Additionally, the variation of void ratio versus soil water content during the wetting and drying cycles showed that the variation was an S-shape curve, which was almost a horizontal S shape for the improved soil. It was observed that the equilibrium 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 variations occurred at saturation degree between 50 and 90%. However, for improved soil sample, the highest void ratio variations were recorded at saturation degree between 70 and 90%, reflecting the reduction of negative effects of water content variations on volume changes when the expansive soil samples were improved. Consequently, it was concluded that the additives used in the study not only decreased the swelling potential of expansive soil samples with very high expansion degree, but also decreased the swelling-shrinkage behaviour of the soil and increased the durability of the samples during wetting and drying cycles.