Abstract: In the design of rockfall protection structure, the cushioning capacity of soils on stone cutoff wall or shed-tunnel against rockfall’s impact force should be taken into consideration properly. PFC2D could simulate the dynamic process of rockfall impacting on the soil and structure effectively. The calculated result of rockfall’s impact force by PFC2D with no consideration of soil’s cushioning capacity is consistent with that by Swedish algorithm (proposed by Dr. Vincent Labiouse) and slightly larger than that by Japanese algorithm (proposed by Japanese Road Association). Furthermore, the impact forces of rockfall from different heights on structure with soil cushions—plain filling soil, silty clay, and sandy silty soil each of different thicknesses—are analyzed. The cushioning capacity of soil is in exponential function relation with soil cushion’s thickness and rockfall’s height; while the influence of falling height on cushioning capacity does not change with the change of soil material. Given the same soil thickness, the cushion capacity of silty clay is the largest, followed by that of plain filling soil and sandy silty soil in sequence. From an economic point of view, the thickness of soil cushion is recommended to be within 2-3 meters in engineering practice.

Key words: protective measures against rockfall, cushioning capacity of soil, rockfall’s impact force, PFC2D, thickness of soil cushion