Enhanced mobility of root-tuber complex driven by fine sand avalanches during tiger nut (Cyperus esculentus L.) harvesting

The enhanced mobility of the root-tuber complex induced by fine sand avalanches exacerbates losses during tiger nut harvesting. Understanding the mechanisms behind enhanced mobility is key to reducing harvest losses, yet the mechanisms involved remain poorly understood. In this work, avalanche behaviour during harvesting was investigated using an inclined chute, and the mechanisms by which fine sand particles enhance the mobility of the root-tuber complex were explored from a granular rheology perspective. The results showed that fine sand particles significantly enhance the mobility of root-tuber complex and almost completely govern its flow behaviour. The Savage number distinguishes two mobility enhancement mechanisms controlled by particle layer thickness, namely friction-dominated and collision-dominated regimes. In the friction-dominated regime, a sand-trap effect causes the root-tuber complex to be entrained by the sand flow and to co-flow with it. In the collision-dominated regime, fine sand particles act as a lubricant beneath the root-tuber complex, thereby promoting its mobility. This study should be useful for achieving low loss and efficient tiger nut harvesting as well as for advancing the understanding of avalanche dynamics in mixtures of dry particles and biomass particles.