Enhancing the shear strength of sand through capsule-enclosed tung oil: a self-healing approach

The development of self-healing soil emerges as a possible solution to provide an autonomous and sustainable geomaterial to ground infrastructure with enhanced durability. This study aimed at developing a capsule-enclosed healant to enhance the shear strength of sand. Encapsulated tung oil was released in sand from calcium alginate capsules when subjected to void ratio changes under compaction. The released tung oil will harden and bond sand grains after a 30-day drying period. The release amount of tung oil was tracked at different void ratios (0.754–0.976) and capsule dosages (0.99%–3.85%), with its effect on strength evaluated by drained triaxial compression tests. The inclusion of capsules with fresh (liquid) tung oil decreased the peak strength and dilatancy of sand. However, enhanced peak strength/stress ratio compared to natural sand at effective confining stress of 50–100 kPa was achieved after stabilization with aged (hardened) tung oil. The critical state line of the sand-capsule composites located below that of clean sand in e-p′ plane, with the lines almost converging in the q-p′ plane. The role of tung oil bonding was separated and explained in terms of bonding energy. The combined effect of capsule dosage and bonding on peak strength were quantitatively captured. The soft capsule decreased friction angle while the bonding contributed to cohesion increase, leading to peak strength enhancement at mean effective stress lower than 500 kPa.