Changes in strength, hydraulic conductivity and microstructure of superabsorbent polymer stabilized soil subjected to wetting-drying cycles

Superabsorbent polymers (SAPs) are environmentally friendly stabilizers to improve the engineering properties of excavated soils with high water contents. The present study aims to evaluate the durability of stabilized soil with SAP subjected to wetting-drying cycles. A series of laboratory experiments were conducted to evaluate the variation in mass loss, unconfined compressive strength (q(u)), hydraulic conductivity, as well as microstructure of stabilized soil exposed to wetting-drying cycles. The results showed that SAP significantly reduced the mass loss, which in turn enhanced q(u) of stabilized soil subjected to wetting-drying cycles. An optimal SAP content was observed in terms of the highest durability index (the ratio of q(u) subjected to wetting-drying cycles to original state). At the early stage of wetting-drying, the durability index increased with the increase in SAP content. Once exceeding the fourth cycle, a further decrease in the durability index was observed at higher SAP contents due to large extent of cracks and spalling on the specimen surface, resulting from the significant water content difference between the inner and outer perimeters. The changes in hydraulic conductivity with wetting-drying cycles were governed by the variation in macro-pore (> 1 mu m) volume. With no wetting-drying cycle, the macro-pore volume increased with SAP, leading to an increase in hydraulic conductivity. After the first cycle, the macro-pores decreased significantly with SAP content, resulting in a decrease in hydraulic conductivity. Up to the fourth cycle, the wetting-drying-induced cracks dominated the water flow path. Thus, the hydraulic conductivity increased with the amount of cracks, leading to a rapid rise of hydraulic conductivity at larger SAP content.