Modelling and verification of the liquorice-soil composite based on pulling test

In the liquorice-soil composite shear test, flexible thick roots bend to create soil resistance which makes measurement results inaccurate. However, the liquorice pulling force characterises the contact strength of the liquorice-soil composite and can be used to study the root-soil interactions. This paper proposed a three-part modelling method to model the liquorice-soil composite at harvesting period. The mechanical parameters of soil particles were calibrated using the soil unconfined compressive strength test. The calibration results showed that the errors of peak force and peak displacement for soil unconfined compressive strength tests were 1.09% and 1.64%, respectively. The flexible liquorice model was constructed based on 3D scanning and particle filling methods, and the simulation model was calibrated based on compression properties. The relative errors in calibration of the flexible liquorice's radial and axial compression forces were 1.35% and 3.9%, respectively. Simplifying liquorice pulling force and liquorice surface area into a linear correlation effectively supports the general modelling method. The contact parameters between soil and liquorice were determined using liquorice pulling force as the target value, and the proportional calibration method was used to improve simulation efficiency. The calibration error for the liquorice pulling force is 4.39%. In addition, the results of the pulling force for the different surface areas show that the calibrated parameters are valid within a liquorice surface area of 0.0075–0.0181 m². This study provided a general and accurate simulation method to the liquorice-soil composite, which can be used as the reference for modelling the long root-soil composite, and provide methodological support for developing root crop harvesters.