A three-dimensional model to predict soil rotary cutting resistance is established besed on the traditional straight soil cutting theory; and the formula is given to calculate the resistance. The model considered the lateral shear failure; and true cutting angle is smaller than tool angle. In order to check the model

test were conducted using different tools in sandy soil; the torque during the expressional test has been gained. The calculated values value fit well with the observed values. The result showed that the nonlinear relationship between the cutting angle and resistance varies for different soil

which optimized cutting angle is existent for different soil. The toothless tool have larger cutting resistance and more sensitive to the cutting angle than the ones with teeth.