Discontinuous deformation analysis (DDA) is a dynamic calculation method implicitly solved, and the block kinematics is obtained by adding or subtracting stiff springs at the contact positions where no tension and no inter-penetration is required. On the basis of an analysis model for block contact iterations, the theoretical formula of the body contact displacement in static condition is deduced, and is verified by contact force calculation. According to the formula, the interrelation between deformation modulus, spring stiffness, time step and contact displacement is researched quantitatively. When deformation modulus and spring stiffness are certain, the variation of contact displacement with time step is obtained. By establishing a simple mechanics model of the block system, the process of the open-close iteration with DDA is analyzed. This research proves that the strategy of using time step to adjust and speed up the open-close iterative convergence proposed by Dr. Shi Genhua is reasonable and efficient. It also reveals the basic rule of determining DDA’s each parameter, and promotes the practical engineering application of DDA.
