Abstract: In view of digging operation of cassava roots planted in red clay, a coupling calculation model is developed to carry out numerical simulation of loosening soil and the precision of the coupling calculation model is verified by physical experiment. Modified Mohr-Coulomb yield criterion, and the coupling algorithm of finite element method (FEM) and smoothed particle hydrodynamics (SPH) are applied in the coupling calculation model. Based on the numerical simulation, loosening soil mechanism of the digging shovel and deformation of cassava roots are studied at micro level. By using quadratic regression general rotary design method and non-dominated sorting generic algorithm (NSGA-Ⅱ), the influence of interactive effect between structural parameters of digging shovel on traction resistance, loosening soil and maximum effective stress of cassava roots are investigated , and the optimal combination of structural parameters is obtained. The results show that the coupling calculation model is suitable for the research on numerical simulation of soil large deformation in digging operation. Soils are bended and thus broken into fragments when they are uplifted by the digging shovel, which is the main reason for soil loosening. Extrusion of soils leads to bending deformation of the cassava roots during soil loosening. With the combination of large penetration angle and small wingspan angle of the shovel, or large penetration angle and large width of the shovel, or large width and small wingspan angle of the shovel, soil loosening is improved. But with the combination of small penetration angle and small wingspan angle of the shovel or large wingspan angle and small width of the shovel, traction resistance would decrease, and with the latter combination, maximum effective stress of cassava roots also decrease. The optimal combination of structural parameters is as follows: penetration angle α=28o, wingspan angle β=64o and shovel width 380 mm. Under such working conditions, the extent of soil loosening is 20.83 mm and traction resistance is 8 641 N.

Key words: Cassava root, Digging shovel, Influence, Mechanism, Numerical simulation, Parameter optimization